evolution of scientific hypothesis

ENCYCLOPEDIC ENTRY

Theory of evolution.

The theory of evolution is a shortened form of the term “theory of evolution by natural selection,” which was proposed by Charles Darwin and Alfred Russel Wallace in the nineteenth century.

Biology, Ecology, Earth Science, Geology, Geography, Physical Geography

Young Charles Darwin

Painting of a young Charles Darwin

Photograph by James L. Stanfield

Ideas aimed at explaining how organisms change, or evolve, over time date back to Anaximander of Miletus, a Greek philosopher who lived in the 500s B.C.E. Noting that human babies are born helpless, Anaximander speculated that humans must have descended from some other type of creature whose young could survive without any help. He concluded that those ancestors must be fish, since fish hatch from eggs and immediately begin living with no help from their parents. From this reasoning, he proposed that all life began in the sea.

Anaximander was correct; humans can indeed trace our ancestry back to fish. His idea, however, was not a theory in the scientific meaning of the word, because it could not be subjected to testing that might support it or prove it wrong. In science, the word “ theory ” indicates a very high level of certainty. Scientists talk about evolution as a theory , for instance, just as they talk about Einstein’s explanation of gravity as a theory .

A theory is an idea about how something in nature works that has gone through rigorous testing through observations and experiments designed to prove the idea right or wrong. When it comes to the evolution of life, various philosophers and scientists, including an eighteenth-century English doctor named Erasmus Darwin, proposed different aspects of what later would become evolutionary theory. But evolution did not reach the status of being a scientific theory until Darwin’s grandson, the more famous Charles Darwin, published his famous book On the Origin of Species . Darwin and a scientific contemporary of his, Alfred Russel Wallace, proposed that evolution occurs because of a phenomenon called natural selection .

In the theory of natural selection, organisms produce more offspring than are able to survive in their environment. Those that are better physically equipped to survive, grow to maturity, and reproduce. Those that are lacking in such fitness, on the other hand, either do not reach an age when they can reproduce or produce fewer offspring than their counterparts. Natural selection is sometimes summed up as “survival of the fittest” because the “fittest” organisms—those most suited to their environment—are the ones that reproduce most successfully, and are most likely to pass on their traits to the next generation.

This means that if an environment changes, the traits that enhance survival in that environment will also gradually change, or evolve. Natural selection was such a powerful idea in explaining the evolution of life that it became established as a scientific theory . Biologists have since observed numerous examples of natural selection influencing evolution . Today, it is known to be just one of several mechanisms by which life evolves. For example, a phenomenon known as genetic drift can also cause species to evolve. In genetic drift , some organisms —purely by chance—produce more offspring than would be expected. Those organisms are not necessarily the fittest of their species, but it is their genes that get passed on to the next generation.

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Darwin: From the Origin of Species to the Descent of Man

This entry offers a broad historical review of the origin and development of Darwin’s theory of evolution by natural selection through the initial Darwinian phase of the “Darwinian Revolution” up to the publication of the Descent of Man in 1871. The development of evolutionary ideas before Darwin’s work has been treated in the separate entry evolutionary thought before Darwin . Several additional aspects of Darwin’s theory of evolution and his biographical development are dealt with in other entries in this encyclopedia (see the entries on Darwinism ; species ; natural selection ; creationism ). The remainder of this entry will focus on aspects of Darwin’s theory not developed in the other entries. It will also maintain a historical and textual approach. Other entries in this encyclopedia cited at the end of the article and the bibliography should be consulted for discussions beyond this point. The issues will be examined under the following headings:

1.1 Historiographical Issues

1.2 darwin’s early reflections, 2.1. the concept of natural selection.

• 2.2. The Argument of the Published Origin

3.1 The Popular Reception of Darwin’s Theory

3.2 the professional reception of darwin’s theory, 4.1 the genesis of darwin’s descent, 4.2 darwin on mental powers, 4.3 the ethical theory of the descent of man.

• 4.4 The Reception of the Descent

5. Summary and Conclusion

Other internet resources, related entries, acknowledgments, 1. the origins of darwin’s theory.

Charles Darwin’s version of transformism has been the subject of massive historical and philosophical scholarship almost unparalleled in any other area of the history of science. This includes the continued flow of monographic studies and collections of articles on particular aspects of Darwin’s theory (Prestes 2023; R. J. Richards and Ruse 2016; Ruse 2013a, 2009a,b,c; Ruse and Richards 2009; Hodge and Radick 2009; Hösle and Illies 2005; Gayon 1998; Bowler 1996; Depew and Weber 1995; Kohn 1985a). The continuous production of popular and professional biographical studies on Darwin provides ever new insights (Ruse et al. 2013a; Johnson 2012; Desmond and Moore 1991, 2009; Browne 1995, 2002; Bowlby 1990; Bowler 1990). In addition, major editing projects on Darwin’s manuscripts and the completion of the Correspondence , project through the entirety of Darwin’s life, continue to reveal details and new insights into the issues surrounding Darwin’s own thought (Keynes [ed.] 2000; Burkhardt et al. [eds] 1985–2023; Barrett et al. [eds.] 1987). The Cambridge Darwin Online website (see Other Internet Resources ) serves as an international clearinghouse for this worldwide Darwinian scholarship, functioning as a repository for electronic versions of all the original works of Darwin, including manuscripts and related secondary materials. It also supplies a continuously updated guide to current literature.

A long tradition of scholarship has interpreted Darwin’s theory to have originated from a framework defined by endemic British natural history, a British tradition of natural theology defined particularly by William Paley (1743–1805), the methodological precepts of John Herschel (1792–1871), developed in his A Preliminary Discourse on the Study of Natural Philosophy (1830 [1987]), and the geological theories of Charles Lyell (1797–1875). His conversion to the uniformitarian geology of Charles Lyell and to Lyell’s advocacy of “deep” geological time during the voyage of the HMS Beagle (December 1831–October 1836), has been seen as fundamental in his formation (Norman 2013; Herbert 2005; Hodge 1983). Complementing this predominantly anglophone historiography has been the social-constructivist analyses emphasizing the origins of Darwin’s theories in British Political Economy (Young 1985: chps. 2, 4, 5). It has also been argued that a primary generating source of Darwin’s inquiries was his involvement with the British anti-slavery movement, a concern reaching back to his revulsion against slavery developed during the Beagle years (Desmond and Moore 2009).

A body of recent historiography, on the other hand, drawing on the wealth of manuscripts and correspondence that have become available since the 1960s (online at Darwin online “Papers and Manuscripts” section, see Other Internet Resources ) has de-emphasized some of the novelty of Darwin’s views and questions have been raised regarding the validity of the standard biographical picture of the early Darwin. These materials have drawn attention to previously ignored aspects of Darwin’s biography. In particular, the importance of his Edinburgh period from 1825–27, largely discounted in importance by Darwin himself in his late Autobiography , has been seen as critical for his subsequent development (Desmond and Moore 1991; Hodge 1985). As a young medical student at the University of Edinburgh (1825–27), Darwin developed a close relationship with the comparative anatomist Robert Edmond Grant (1793–1874) through the student Plinian Society, and in many respects Grant served as Darwin’s first mentor in science in the pre- Beagle years (Desmond and Moore 1991, chp. 1). Through Grant he was exposed to the transformist theories of Jean Baptiste Lamarck and the Cuvier-Geoffroy debate centered on the Paris Muséum nationale d’histoire naturelle (see entry on evolutionary thought before Darwin , Section 4).

These differing interpretive frameworks make investigations into the origins of Darwin’s theory an active area of historical research. The following section will explore these origins.

In its historical origins, Darwin’s theory was different in kind from its main predecessors in important ways (Ruse 2013b; Sloan 2009a; see also the entry on evolutionary thought before Darwin ). Viewed against a longer historical scenario, Darwin’s theory does not deal with cosmology or the origins of the world and life through naturalistic means, and therefore was more restricted in its theoretical scope than its main predecessors influenced by the reflections of Georges Louis LeClerc de Buffon (1707–1788), Johann Herder (1744–1803, and German Naturphilosophen inspired by Friederich Schelling (1775–1854) . This restriction also distinguished Darwin’s work from the grand evolutionary cosmology put forth anonymously in 1844 by the Scottish publisher Robert Chambers (1802–1871) in his immensely popular Vestiges of the Natural History of Creation , a work which in many respects prepared Victorian society in England, and pre-Civil War America for the acceptance of a general evolutionary theory in some form (Secord 2000; MacPherson 2015). It also distinguishes Darwin’s formulations from the theories of his contemporary Herbert Spencer (1820–1903).

Darwin’s theory first took written form in reflections in a series of notebooks begun during the latter part of the Beagle voyage and continued after the return of the Beagle to England in October of 1836 (Barrett et al., 1987). His reflections on the possibility of species change are first entered in March of 1837 (“Red Notebook”) and are developed in the other notebooks (B–E) through July of 1839 (Barrett et al. 1987; Hodge 2013a, 2009). Beginning with the reflections of the third or “D” “transmutation” Notebook, composed between July and October of 1838, Darwin first worked out the rudiments of what was to become his theory of natural selection. In the parallel “M” and “N” Notebooks, dating between July of 1838 and July of 1839, and in a loose collection called “Old and Useless Notes”, dating from approximately 1838–40, he also developed many of his main ideas on human evolution that would only be made public in the Descent of Man of 1871 (below, Section 4).

To summarize a complex issue, these Notebook reflections show Darwin proceeding through a series of stages in which he first formulated a general theory of the transformation of species by historical descent from common ancestors. He then attempted to work out a causal theory of life that would explain the tendency of life to complexify and diversify (Hodge 2013a, 2009, 1985; Sloan 1986). This causal inquiry into the underlying nature of life, and with it the search for an explanation of life’s innate tendency to develop and complexify, was then replaced by a dramatic shift in focus away from these inquiries. This concern with a causal theory of life was then replaced by a new emphasis on external forces controlling population, a thesis developed from his reading of Thomas Malthus’s (1766–1834) Essay on the Principle of Population (6th ed. 1826). For Malthus, human populaton was assumed to expand geometrically, while food supply expanded arithmetically, leading to an inevitable struggle of humans for existence. The impact of Darwin’s reading of this edition of the Essay in August of 1838, was dramatic. It enabled him to theorize the existence of a constantly-acting dynamic force behind the transformation of species.

Darwin’s innovation was to universalize the Malthusian “principle of population” to apply to all of nature. In so doing, Darwin effectively introduced what may be termed an “inertial” principle into his theory, although such language is never used in his text. Newton’s first law of motion, set forth in his Mathematical Principles of Natural Philosophy (1st ed. 1687), established his physical system upon the tendency of all material bodies to persist eternally either at rest or in uniform motion in a straight line, requiring a causal force explanation for any deviations from this initial state. But Newton did not seek a deeper metaphysical explanation of this inertial state. Law One is simply an “axiom” in Newton’s Principia. Similarly, the principle of population supplied Darwin with the assumption of an initial dynamic state of affairs that was not itself explained within the theory—there is no attempt to account causally for this tendency of living beings universally to reproduce geometrically. Similarly for Darwin, the principle of population functions axiomatically, defining a set of initial conditions from which any deviance from this ideal state demands explanation.

This theoretical shift enabled Darwin to bracket his earlier efforts to develop a causal theory of life, and focus instead on the means by which the dynamic force of population was controlled. This allowed him to emphasize how controls on population worked in company with the phenomenon of slight individual variation between members of the same species, in company with changing conditions of life, to produce a gradual change of form and function over time, leading to new varieties and eventually to new species. This opened up the framework for Darwin’s most important innovation, the concept of “natural” selection.

2. Darwinian Evolution

The primary distinguishing feature of Darwin’s theory that separates it from previous explanations of species change centers on the causal explanation he offered for how this process occurred. Prior theories, such as the theory of Jean-Baptiste Lamarck (see entry on evolutionary thought before Darwin ), relied on the inherent dynamic properties of matter. The change of species was not, in these pre-Darwinian efforts, explained through an adaptive process. Darwin’s emphasis after the composition of Notebook D on the factors controlling population increase, rather than on a dynamic theory of life grounded in vital forces, accounts for many of the differences between Darwin’s theory and those of his predecessors and contemporaries.

These differences can be summarized in the concept of natural selection as the central theoretical component of Darwinian theory. However, the exact meaning of this concept, and the varying ways he stated the principle in the Origin over its six editions (1859–1872), has given rise to multiple interpretations of the meaning of this principle in the history of Darwinism, and the different understandings of his meaning deeply affected different national and cultural receptions of his theory (see below, Section 3 .1).

One way to see the complexity of Darwin’s own thinking on these issues is to follow the textual development of this concept from the close of the Notebook period (1839) to the publication of the Origin of Species in 1859. This period of approximately twenty years involved Darwin in a series of reflections that form successive strata in the final version of his theory of the evolution of species. Understanding the historical sequence of these developments also has significance for subsequent controversies over this concept and the different readings of the Origin as it went through its successive revisions. This historical development of the concept also has some bearing on assessing Darwin’s relevance for more general philosophical questions, such as those surrounding the relevance of his theory for such issues as the concept of a more general teleology of nature.

The earliest set of themes in the manuscript elaboration of natural selection theory can be characterized as those developed through a particular form of the argument from analogy. This took the form of a strong “proportional” form of the analogical argument that equated the relation of human selection to the development of domestic breeds as an argument of the basic form: human selection is to domestic variety formation as natural selection is to natural species formation (White, Hodge and Radick 2021, chps. 4–5). This makes a direct analogy between the actions of nature with those of humans in the process of selection. The specific expressions, and changes, in this analogy are important to follow closely. As this was expressed in the first coherent draft of the theory, a 39-page pencil manuscript written in 1842, this discussion analogized the concept of selection of forms by human agency in the creation of the varieties of domestic animals and plants, to the active selection in the natural world by an almost conscious agency, a “being infinitely more sagacious than man (not an omniscient creator)” who acts over “thousands and thousands of years” on “all the variations which tended towards certain ends” (Darwin 1842 in Glick and Kohn 1996, 91). This agency selects out those features most beneficial to organisms in relation to conditions of life, analogous in its action to the selection by man on domestic forms in the production of different breeds. Interwoven with these references to an almost Platonic demiurge are appeals to the selecting power of an active “Nature”:

Nature’s variation far less, but such selection far more rigid and scrutinizing […] Nature lets <<an>> animal live, till on actual proof it is found less able to do the required work to serve the desired end, man judges solely by his eye, and knows not whether nerves, muscles, arteries, are developed in proportion to the change of external form. (Ibid., 93)

These themes were continued in the 230 page draft of his theory of 1844. Again he referred to the selective action of a wise “Being with penetration sufficient to perceive differences in the outer and innermost organization quite imperceptible to man, and with forethought extending over future centuries to watch with unerring care and select for any object the offspring of an organism produced” (Darwin 1844 in ibid., 101). This selection was made with greater foresight and wisdom than human selection. As he envisions the working of this causal agency,

In accordance with the plan by which this universe seems governed by the Creator, let us consider whether there exist any secondary means in the economy of nature by which the process of selection could go on adapting, nicely and wonderfully, organisms, if in ever so small a degree plastic, to diverse ends. I believe such secondary means do exist. (Ibid., 103).

Darwin returned to these issues in 1856, following a twelve-year period in which he published his Geological Observations on the Volcanic Islands (1844), the second edition of his Journal of Researches (1845), Geological Observations on South America (1846), the four volumes on fossil and living barnacles ( Cirripedia ) (1851, 54, 55), and Geological Observations on Coral Reefs (1851). In addition, he published several smaller papers on invertebrate zoology and on geology, and reported on his experiments on the resistance of seeds to salt water, a topic that would be of importance in his explanation of the population of remote islands.

These intervening inquiries positioned Darwin to deal with the question of species permanence against an extensive empirical background. The initial major synthesis of these investigations takes place in his long manuscript, or “Big Species Book”, commenced in 1856, known in current scholarship as the “Natural Selection” manuscript. This formed the immediate background text behind the published Origin . Although incomplete, the “Natural Selection” manuscript provides insights into many critical issues in Darwin’s thinking. It was also prepared with an eye to the scholarly community. This distinguishes its content and presentation from that of the subsequent “abstract” which became the published Origin of Species . “Natural Selection” contained tables of data, references to scholarly literature, and other apparatus expected of a non-popular work, none of which appeared in the published Origin .

The “Natural Selection” manuscript also contained some new theoretical developments of relevance to the concept of natural selection that are not found in earlier manuscripts. Scholars have noted the introduction in this manuscript of the “principle of divergence”, the thesis that organisms under the action of natural selection will tend to radiate and diversify within their “conditions of life”—the contemporary name for the complex of environmental and species-interaction relationships (Kohn 1985b, 2009). Although the concept of group divergence under the action of natural selection might be seen as an implication of Darwin’s theory from his earliest formulations of the 1830s, nonetheless Darwin’s explicit definition of this as a “principle”, and its discussion in a long late insertion in the “Natural Selection” manuscript, suggests its importance for Darwin’s mature theory. The principle of divergence was now seen by Darwin to form an important link between natural variation and the conditions of existence under the action of the driving force of population increase.

Still evident in the “Natural Selection” manuscript is Darwin’s implicit appeal to some kind of teleological ordering of the process. The action of the masculine-gendered “wise being” of the earlier manuscripts, however, has now been given over entirely to the action of a selective “Nature”, now referred to in the traditional feminine gender. This Nature,

…cares not for mere external appearance; she may be said to scrutinise with a severe eye, every nerve, vessel & muscle; every habit, instinct, shade of constitution,—the whole machinery of the organisation. There will be here no caprice, no favouring: the good will be preserved & the bad rigidly destroyed.… Can we wonder then, that nature’s productions bear the stamp of a far higher perfection than man’s product by artificial selection. With nature the most gradual, steady, unerring, deep-sighted selection,—perfect adaption [sic] to the conditions of existence.… (Darwin 1856–58 [1974: 224–225])

The language of this passage, directly underlying statements about the action of “natural selection” in the first edition of the published Origin , indicates the complexity in the exegesis of Darwin’s meaning of “natural selection” when viewed in light of its historical genesis (Ospovat 1981). The parallels between art and nature, the intentionality implied in the term “selection”, the notion of “perfect” adaptation, and the substantive conception of “nature” as an agency working toward certain ends, all render Darwin’s views on teleological purpose more complex than they are typically interpreted from the standpoint of contemporary Neo-selectionist theory (Lennox 1993, 2013). As will be discussed below, the changes Darwin subsequently made in his formulations of this concept over the history of the Origin have led to different conceptions of what he meant by this principle.

The hurried preparation and publication of the Origin between the summer of 1858 and November of 1859 was prompted by the receipt on June 18 of 1858 of a letter and manuscript from Alfred Russel Wallace (1823–1913) that outlined his remarkably similar views on the possibility of continuous species change under the action of a selection upon natural variation (Wallace 1858 in Glick and Kohn 1996, 337–45). This event had important implications for the subsequent form of Darwin’s published argument. Rapidly condensing the detailed arguments of the unfinished “Natural Selection” manuscript into shorter chapters, Darwin also universalized several claims that he had only developed with reference to specific groups of organisms, or which he had applied only to more limited situations in the manuscript. This resulted in a presentation of his theory at the level of broad generalization. The absence of tables of data, detailed footnotes, and references to the secondary literature in the published version also resulted in predictable criticisms which will be discussed below in Section 3.2 .

2.2. The Central Argument of the Published Origin

The Origin of Species by Means of Natural Selection, or the Preservaton of Favoured Races in the Struggle for Life was issued in London by the publishing house of John Murray on November 24, 1859 (Darwin 1859 [1964]). The structure of the argument presented in the published Origin has been the topic of considerable literature and can only be summarized here. Although Darwin himself described his book as “one long argument”, the exact nature of this argument is not immediately transparent, and alternative interpretations have been made of his reasoning and rhetorical strategies in formulating his evolutionary theory. (Prestes 2023; White, Hodge and Radick 2021; Hodge 2013b, 1977; Hoquet 2013; Hull 2009; Waters 2009; Depew 2009; Ruse 2009; Lennox 2005; Hodge 1983b).

The scholarly reconstruction of Darwin’s methodology employed in the Origin has taken two primary forms. One approach has been to reconstruct it from the standpoint of currently accepted models of scientific explanation, sometimes presenting it as a formal deductive model (Sober 1984). Another, more historical, approach interprets his methodology in the context of accepted canons of scientific explanation found in Victorian discussions of the period (see the entry on Darwinism ; Prestes 2023; White, Hodge and Radick 2021; Hodge 2013b, 1983b, 1977; Hoquet 2013; Hull 2009; Waters 2009; Depew 2009; Lennox 2005). The degree to which Darwin did in fact draw from the available methodological discussions of his contemporaries—John Herschel, William Whewell, John Stuart Mill—is not fully clear from available documentary sources. The claim most readily documented, and defended particularly by White, Hodge and Radick (2021) and M. J. S. Hodge (1977, 1983a), has emphasized the importance of John Herschel’s A Preliminary Discourse on the Study of Natural Philosophy (1830 [1987]), which Darwin read as a young student at Cambridge prior to his departure on the HMS Beagle in December of 1831.

In Herschel’s text he would have encountered the claim that science seeks to determine “true causes”— vera causae— of phenomena through the satisfaction of explicit criteria of adequacy (Herschel, 1830 [1987], chp. 6). This concept Newton had specified in the Principia as the third of his “Rules of Reasoning in Philosophy” (see the entry on Newton’s philosophy , Section 4). Elucidation of such causes was to be the goal of scientific explanation. Vera causae , in Herschel’s formulation, were those necessary to produce the given effects; they were truly active in producing the effects; and they adequately explained these effects.

The other plausible methodological source for Darwin’s mature reasoning was the work of his older contemporary and former Cambridge mentor, the Rev. William Whewell (1794–1866), whose three-volume History of the Inductive Sciences (Whewell 1837) Darwin read with care after his return from his round-the-world voyage (Ruse 2013c, 1975). On this reading, a plausible argument has been made that the actual structure of Darwin’s text is more closely similar to a “Whewellian” model of argument. In Whewell’s accounts of his philosophy of scientific methodology (Whewell 1840, 1858), the emphasis of scientific inquiry is, as Herschel had also argued, to be placed on the discovery of “true causes”. But evidence for the determination of a vera causa was to be demonstrated by the ability of disparate phenomena to be drawn together under a single unifying “Conception of the Mind”, exemplified for Whewell by Newton’s universal law of gravitation. This “Consilience of Inductions”, as Whewell termed this process of theoretical unification under a few simple concepts, was achieved only by true scientific theories employing true causes (Whewell 1840: xxxix). It has therefore been argued that Darwin’s theory fundamentally produces this kind of consilience argument, and that his methodology is more properly aligned with that of Whewell.

A third account, related to the Whewellian reading, is that of David Depew. Building on Darwin’s claim that he was addressing “the general naturalist public,” Darwin is seen as developing what Depew has designated as “situated argumentation”, similar to the views developed by contemporary Oxford logician and rhetorical theorist Richard Whately (1787–1863) (Depew 2009). This rhetorical strategy proceeds by drawing the reader into Darwin’s world by personal narration as it presents a series of limited issues for acceptance in the first three chapters, none of which required of the reader a considerable leap of theoretical assent, and most of which, such as natural variation and Malthusian population increase, had already been recognized in some form in the literature of the period.

As Darwin presented his arguments to the public, he opens with a pair of chapters that draw upon the strong analogy developed in the manuscripts between the action of human art in the production of domestic forms, and the actions of selection “by nature.” The resultant forms are presumed to have arisen through the action of human selection on the slight variations existing between individuals within the same species. The interpretation of this process as implying directional, and even intentional, selection by a providential “Nature” that we have seen in the manuscripts was, however, downplayed in the published work through the importance given by Darwin to the role of “unconscious” selection, a concept not encountered in the Natural Selection manuscript. Such selection denotes the practice even carried out by aboriginal peoples who simply seek to maintain the integrity and survival of a breed or species by preserving the “best” forms.

The domestic breeding analogy is, however, more than a decorative rhetorical strategy. It repeatedly functions for Darwin as the principal empirical example to which he could appeal at several places in the text as a means of visualizing the working of natural selection in nature, and this appeal remains intact through the six editions of the Origin.

From this model of human selection working on small individual natural variations to produce the domestic forms, Darwin then developed in the second chapter the implications of “natural” variation, delaying discussion of the concept of natural selection until Chapter IV. The focus of the second chapter introduces another important issue. Here he extends the discussion of variation developed in Chapter I into a critical analysis of the common understanding of classification as grounded on the definition of species and higher groups based on the possession of essential defining properties. It is in this chapter that Darwin most explicitly develops his own position on the nature of organic species in relation to his theory of descent. It is also in this chapter that he sets forth the ingredients for his attack on one meaning of species “essentialism”.

Darwin’s analysis of the “species question” involves a complex argument that has many implications for how his work was read by his contemporaries and successors, and its interpretation has generated a considerable literature (see the entries on species and Darwinism ; Mallet 2013; R. A. Richards 2010; Wilkins 2009; Stamos 2007; Sloan 2009b, 2013; Beatty 1985).

Prior tradition had been heavily affected by eighteenth-century French naturalist Buffon’s novel conception of organic species in which he made a sharp distinction between “natural” species, defined primarily by fertile interbreeding, and “artificial” species and varieties defined by morphological traits and measurements upon these (see the entry on evolutionary thought before Darwin , Section 3.3). This distinction was utilized selectively by Darwin in an unusual blending of two traditions of discussion that are conflated in creative ways in Darwin’s analysis.

Particularly as the conception of species had been discussed by German natural historians of the early nineteenth-century affected by distinctions introduced by philosopher Immanuel Kant (1724–1804), “Buffonian” species were defined by the material unity of common descent and reproductive continuity. This distinguished them by their historical and material character from the taxonomic species of the “Linnean” tradition of natural history. This distinction between “natural” and “logical” species had maintained a distinction between problems presented in the practical classification of preserved specimens, distinguished by external characters, and those relating to the unity of natural species, which was grounded upon reproductive unity and the sterility criterion (Sloan 2009b).

Remarkable in Darwin’s argument is the way in which he draws selectively in his readings from these two preexistent traditions to undermine the different grounds of species “realism” assumed within both of these traditions of discourse. One framework—what can be considered in his immediate context the “Linnean” tradition—regarded species in the sense of universals of logic or class concepts, whose “reality” was often grounded on the concept of divine creation. The alternative “Buffonian” tradition viewed species more naturalistically as material lineages of descent whose continuity was determined by some kind of immanent principle, such as the possession of a conserving “internal mold” or specifying vital force (see evolutionary thought before Darwin 3.3). The result in Darwin’s hands is a complex terminological interweaving of concepts of Variety, Race, Sub-species, Tribe, and Family that can be shown to be a fusion of different traditions of discussion in the literature of the period. This creative conflation also led to many confusions among his contemporaries about how Darwin actually did conceive of species and species change in time.

Darwin addresses the species question by raising the problems caused by natural variation in the practical discrimination of taxa at the species and varietal levels, an issue with which he had become closely familiar in his taxonomic revision of the Sub-class Cirripedia (barnacles) in his eight-year study on this group. Although the difficulty of taxonomic distinctions at this level was a well-recognized problem in the literature of the time, Darwin subtly transforms this practical problem into a metaphysical ambiguity—the fuzziness of formal taxonomic distinctions created by variation in preserved specimens is seen to imply a similar ambiguity of “natural” species boundaries.

We follow this in reading how natural variation is employed by Darwin in Chapter Two of the Origin to break down the distinction between species and varieties as these concepts were commonly employed in the practical taxonomic literature. The arbitrariness apparent in making distinctions, particularly in plants and invertebrates, meant that such species were only what “naturalists having sound judgment and wide experience” defined them to be ( Origin 1859 [1964], 47). These arguments form the basis for claims by his contemporaries that Darwin was a species “nominalist”, who defined species only as conventional and convenient divisions of a continuum of individuals.

But this feature of Darwin’s discussion of species captures only in part the complexity of his argument. Drawing also on the tradition of species realism developed within the “Buffonian” tradition, Darwin also affirmed that species and varieties are defined by common descent and material relations of interbreeding. Darwin then employed the ambiguity of the distinction between species and varieties created by individual variation in practical taxonomy to undermine the ontological fixity of “natural” species. Varieties are not simply the formal taxonomic subdivisions of a natural species as conceived in the Linnaean tradition. They are, as he terms them, “incipient” species (ibid., 52). This subtly transformed the issue of local variation and adaptation to circumstances into a primary ingredient for historical evolutionary change. The full implications to be drawn from this argument were, however, only to be revealed in Chapter Four of the text.

Before assembling the ingredients of these first two chapters, Darwin then introduced in Chapter Three the concept of a “struggle for existence”. This concept is introduced in a “large and metaphorical sense” that included different levels of organic interactions, from direct struggle for food and space to the struggle for life of a plant in a desert. Although described as an application of Thomas Malthus’s parameter of geometrical increase of population in relation to the arithmetical increase of food supply, Darwin’s use of this concept in fact reinterprets Malthus’s principle, which was formulated only with reference to human population in relation to food supply. It now becomes a general principle governing all of organic life. Thus all organisms, including those comprising food for others, would be governed by the tendency to geometrical increase.

Through this universalization, the controls on population become only in the extreme case grounded directly on the traditional Malthusian limitations of food and space. Normal controls are instead exerted through a complex network of relationships of species acting one on another in predator-prey, parasite-host, and food-web relations. This profound revision of Malthus’s arguments rendered Darwin’s theory deeply “ecological” as this term would later be employed. We can cite two thought experiments employed by Darwin himself as illustrations (ibid., 72–74). The first concerns the explanation of the abundance of red clover in England. This Darwin sees as dependent on the numbers of pollinating humble bees, which are controlled in turn by the number of mice, and these are controlled by the number of cats, making cats the remote determinants of clover abundance. The second instance concerns the explanation of the abundance of Scotch Fir. In this example, the number of fir trees is limited indirectly by the number of cattle.

With the ingredients of the first three chapters in place, Darwin was positioned to assemble these together in his grand synthesis of Chapter Four on “natural” selection. In this long discussion, Darwin develops the main exposition of his central theoretical concept. For his contemporaries and for the subsequent tradition, however, the meaning of Darwin’s concept of “natural” selection was not unambiguously evident for reasons we have outlined above, and these unclarities were to be the source of several persistent lines of disagreement and controversy.

The complexities in Darwin’s presentation of his central principle over the six editions of the published Origin served historically to generate several different readings of his text. In the initial introduction of the principle of natural selection in the first edition of Darwin’s text, it is characterized as “preservation of favourable variations and the rejection of injurious variations” (ibid., 81). When Darwin elaborated on this concept in Chapter Four of the first edition, he continued to describe natural selection in language suggesting that it involved intentional selection, continuing the strong art-nature analogy found in the manuscripts. For example:

As man can produce and certainly has produced a great result by his methodical and unconscious means of selection, what may not nature effect? Man can act only on external and visible characters: nature cares nothing for appearances, except in so far as they may be useful to any being. She can act on every internal organ, on every shade of constitutional difference, on the whole machinery of life. Man selects only for his own good; Nature only for that of the being which she tends. Every selected character is fully exercised by her; and the being is placed under well-suited conditions of life. (Ibid., 83)

The manuscript history behind such passages prevents the simple discounting of these statements as mere rhetorical imagery. As we have seen, the parallel between intentional human selectivity and that of “nature” formed the proportional analogical model upon which the concept of natural selection was originally constructed.

Criticisms that quickly developed over the overt intentionality embedded in such passages, however, led Darwin to revise the argument in editions beginning with the third edition of 1861. From this point onward he explicitly downplayed the intentional and teleological language of the first two editions, denying that his appeals to the selective role of “nature” were anything more than a literary figure. Darwin then moved decisively in the direction of defining natural selection as the description of the action of natural laws working upon organisms rather than as an efficient or final cause of life. He also regrets in his Correspondence his mistake in not utilizing the designation “natural preservation” rather than “natural selection” to characterize his principle (letter to Lyell 28 September 1860, Burkhardt Correspondence 8, 397; also see Darwin Correspondence Project in Other Internet Resources ). In response to criticisms of Alfred Russel Wallace, Darwin then adopted in the fifth edition of 1869 his contemporary (1820–1903) Herbert Spencer’s designator, “survival of the fittest”, as a synonym for “natural selection” (Spencer 1864, 444–45; Darwin 1869, 72). This redefinition further shifted the meaning of natural selection away from the concept that can be extracted from the early texts and drafts. These final statements of the late 1860s and early 70s underlie the tradition of later “mechanistic” and non-teleological understandings of natural selection, a reading developed by his disciples who, in the words of David Depew, “had little use for either his natural theodicy or his image of a benignly scrutinizing selection” (Depew 2009, 253). The degree to which this change preserved the original strong analogy between art and nature can, however, be questioned. Critics of the use of this analogy had argued since the original formulations that the comparison of the two modes of selection actually worked against Darwin’s theory (Wallace 1858 in Glick and Kohn 1997, 343). This critique would also be leveled against Darwin in the critical review of 1867 by Henry Fleeming Jenkin discussed below.

The conceptual synthesis of Chapter Four also introduced discussions of such matters as the conditions under which natural selection most optimally worked, the role of isolation, the causes of the extinction of species, and the principle of divergence. Many of these points were made through the imaginative use of “thought experiments” in which Darwin constructed possible scenarios through which natural selection could bring about substantial change.

One prominent way Darwin captured for the reader the complexity of this process is reflected in the single diagram to appear in all the editions of the Origin . In this illustration, originally located as an Appendix to the first edition, but thereafter moved into Chapter Four, Darwin summarized his conception of how species were formed and diverged from common ancestral points. This image also served to depict the frequent extinction of most lineages, an issue developed in detail in Chapter Ten. It displayed pictorially the principle of divergence, illustrating the general tendency of populations to diverge and fragment under the pressure of population increase. It supplied a way of envisioning relations of taxonomic affinity to time, and illstrated the persistence of some forms unchanged over long geological periods in which stable conditions prevail.

Figure: Tree of life diagram from Origin of Species ( Origin 1859:“Appendix”.

Remarkable about Darwin’s diagram of the tree of life is the relativity of its coordinates. It is first presented as applying only to the divergences taking place in taxa at the species level, with varieties represented by the small lower-case letters within species A–L of a “wide ranging genus”, with the horizontal lines representing time segments measured in terms of a limited number of generations. However, the attentive reader could quickly see that Darwin’s destructive analysis of the distinction between “natural” and “artificial” species in Chapter Two, implied the relativity of the species-variety distinction, this diagram could represent eventually all organic relationships, from those at the non-controversial level of diverging varieties within fixed species, to those of the relations of Species within different genera. Letters A–L could also represent taxa at the level of genera, families or orders. The diagram can thus be applied to relationships between all levels of the Linnaean hierarchy with the time segments representing potentially vast expanses of time, and the horizontal spread of branches the degree of taxonomic divergence over time. In a very few pages of argument, the diagram was generalized to represent the most extensive group relations, encompassing the whole of geological time. Extension of the dotted lines at the bottom could even suggest, as Darwin argues in the last paragraph of the Origin , that all life was a result of “several powers, having been originally breathed into a few forms or into one” (Darwin 1859 [1964], 490). This could suggest a single naturalistic origin of all original forms either by material emergence, or through the action of a vitalistic power of life. Darwin’s use of Biblical language could also be read as allowing for the action of a supernatural cause.

In response to criticisms concerning this latter point, Darwin quickly added to the final paragraph in the second edition of 1860 the phrase “by the Creator” (1860: 484), which remained in all subsequent editions. as did the quotations on the frontispiece from familiar discussions in British natural theology concerning creation by secondary causation. Conceptual space was thereby created for the reading of the Origin by some contemporaries, notably by the Harvard botanist Asa Gray (1810–88), as compatible with traditional natural theology (Gray 1860).

The sweep of the theoretical generalization that closed the natural selection chapter, one restated even more generally in the final paragraph of the book, required Darwin to deal with several obvious objections to the theory that constitute the main “defensive” chapters of the Origin (Five–Nine), and occupy him through the numerous revisions of the text between 1859 and 1872. As suggested by David Depew, the rhetorical structure of the original text developed in an almost “objections and response” structure that resulted in a constant stream of revisions to various editions of the original text as Darwin engaged his opponents (Depew 2009; Peckham 2006). Anticipating at first publication several obvious lines of objection, Darwin devoted much of the text of the original Origin to offering a solution in advance to predictable difficulties. As Darwin outlined these main lines of objection, he discussed, first, the apparent absence of numerous slight gradations between species, both in the present and in the fossil record, of the kind that would seem to be predictable from the gradualist workings of the theory (Chps. Six, Nine). Second, the gradual development of organs and structures of extreme complexity, such as the vertebrate eye, an organ which had since Antiquity served as a mainstay of the argument for external teleological design (Chp. Six). Third, the evolution of the elaborate instincts of animals and the puzzling problem of the evolution of social insects that developed sterile neuter castes, proved to be a particularly difficult issue for Darwin in the manuscript phase of his work and needed some account (Chp. Seven). As a fourth major issue needing attention, the traditional distinction between natural species defined by interfertility, and artificial species defined by morphological differences, required an additional chapter of analysis in which he sought to undermine the absolute character of the interbreeding criterion as a sign of fixed natural species (Chp. Eight).

In Chapter Ten, Darwin developed his interpretation of the fossil record. At issue was the claim by Lamarckian and other transformists, as well as Cuvierian catastrophists such as William Buckland (1784–1856) (see the entry on evolutionary thought before Darwin , Section 4.1), that the fossil record displayed a historical sequence beginning with simpler plants and animals, arriving either by transformism or replacement, at the appearance of more complex forms in geological history. Opposition to this thesis of “geological progressionism” had been made by none other than Darwin’s great mentor in geology, Charles Lyell in his Principles of Geology (Lyell 1832 [1990], vol. 2, chp. xi; Desmond 1984; Bowler 1976). Darwin defended the progressionist view against Lyell’s arguments in this chapter.

To each of the lines of objection to his theory, Darwin offered his contemporaries plausible replies. Additional arguments were worked out through the insertion of numerous textual insertions over the five revisions of the Origin between 1860 and 1872, including the addition of a new chapter to the sixth edition dealing with “miscellaneous” objections, responding primarily to the criticisms of St. George Jackson Mivart (1827–1900) developed in his Genesis of Species (Mivart 1871).

For reasons related both to the condensed and summary form of public presentation, and also as a reflection of the bold conceptual sweep of the theory, the primary argument of the Origin could not gain its force from the data presented by the book itself. Instead, it presented an argument from unifying simplicity, gaining its force and achieving assent from the ability of Darwin’s theory to draw together in its final synthesizing chapters (Ten–Thirteen) a wide variety of issues in taxonomy, comparative anatomy, paleontology, biogeography, and embryology under the simple principles worked out in the first four chapters. This “consilience” argument might be seen as the best reflection of the impact of William Whewell’s methodology (see above).

As Darwin envisioned the issue, with the acceptance of his theory, “a grand untrodden field of inquiry will be opened” in natural history. The long-standing issues of species origins, if not the the explanation of the ultimate origins of life, as well as the causes of their extinction, had been brought within the domain of naturalistic explanation. It is in this context that he makes the sole reference in the text to the claim that “light will be thrown on the origin of man and his history”. And in a statement that will foreshadow the important issues of the Descent of Man of 1871, he speaks of how “Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation” (ibid., 488)

3. The Reception of the Origin

The broad sweep of Darwin’s claims, the brevity of the empirical evidence actually supplied in the Origin , and the implications of his theory for several more general philosophical and theological issues, opened up a controversy over Darwinian evolution that has waxed and waned over more than 160 years. The theory was inserted into a complex set of different national and cultural receptions the study of which currently forms a scholarly industry in its own right. European, Latin American and Anglophone receptions have been most deeply studied (Bowler 2013a; Gayon 2013; Largent 2013; Glick 1988, 2013; Glick and Shaffer 2014; Engels and Glick 2008; Gliboff 2008; Numbers 1998; Pancaldi, 1991; Todes 1989; Kelly 1981; Hull 1973; Mullen 1964). To these have been added analyses of non-Western recptions (Jin 2020, 2019 a,b; Yang 2013; Shen 2016; Elshakry 2013; Pusey 1983). These analyses display common patterns in both Western and non-Western readings of Darwin’s theory, in which these receptions were conditioned, if not determined, by the pre-existing intellectual, scientific, religious, social, and political contexts into which his works were inserted.

In the anglophone world, Darwin’s theory fell into a complex social environment that in the United States meant into the pre-Civil War slavery debates (Largent 2013; Numbers 1998). In the United Kingdom it was issued against the massive industrial expansion of mid-Victorian society, and the development of professionalized science. To restrict focus to aspects of the British reading public context, the pre-existing popularity of the anonymous Vestiges of the Natural History of Creation of 1844, which had reached 11 editions and sold 23,350 copies by December of 1860 (Secord “Introduction” to Chambers 1844 [1994], xxvii]), with more editions to appear by the end of the century, certainly prepared the groundwork for the general notion of the evolutionary origins of species by the working of secondary natural laws. The Vestiges ’s grand schema of a teleological development of life, from the earliest beginnings of the solar system in a gaseous nebula to the emergence of humanity under the action of a great “law of development”, had also been popularized for Victorian readers by Alfred Lord Tennyson’s epic poem In Memoriam (1850). This Vestiges backdrop provided a context in which some could read Darwin as supplying additional support for the belief in an optimistic historical development of life under teleological guidance of secondary laws with the promise of ultimate historical redemption. Such readings also rendered the Origin seemingly compatible with the progressive evolutionism of Darwin’s contemporary Herbert Spencer (see the entry on Herbert Spencer ). Because of these similarities, Spencer’s writings served as an important vehicle by which Darwin’s views, modified to fit the progressivist views expounded by Spencer, were first introduced in non-Western contexts (Jin 2020, 2019 a,b; Lightman [ed.] 2015; Pusey 1983). Such popular receptions ignored or revised Darwin’s concept of evolution by natural selection to fit these progressivist alternatives.

Outside the United Kingdom, the receptions of Darwin’s work display the importance of local context and pre-existent intellectual and social conditions. Three examples—France, Germany, and China—can be elaborated upon. In France, Darwin’s theory was received against the background of the prior debates over transformism of the 1830s that pitted the theories of Lamarck and Etienne Geoffroy St. Hilaire against Cuvier (Gayon 2013; entry on evolutionary thought before Darwin , 4.1). At least within official French Academic science, these debates had been resolved generally in favor of Cuvier’s anti-transformism. The intellectual framework provided by the “positive philosophy” of Auguste Comte (1798–1857) also worked both for and against Darwin. On one hand, Comte’s emphasis on the historical progress of science over superstition and metaphysics allowed Darwin to be summoned in support of a theory of the progress of science. The Origin was so interpreted in the preface to the first French translation of the Origin made by Clémence Royer (Harvey 2008). On the other hand, the Comtean three stages view of history, with its claim of the historical transcendence of speculative and metaphysical periods of science by a final period of experimental science governed by determinate laws, placed Darwinism in a metaphysical phase of speculative nature philosophy. This view is captured by the assessment of the leading physiologist and methodologist of French Science, Claude Bernard (1813–78). As he stated this in his 1865 treatise on scientific methodology, Darwin’s theory was to be regarded with those of “a Goethe, an Oken, a Carus, a Geoffroy Saint Hilaire”, locating it within speculative philosophy of nature rather than granting it the status of “positive” science (Bernard 1865 [1957], 91–92]).

In the Germanies, Darwin’s work entered a complex social, intellectual and political situation in the wake of the failed efforts to establish a liberal democracy in 1848. It also entered an intellectual culture strongly influenced by the pre-existent philosophical traditions of Kant, Schelling’s Naturphilosophie , German Romanticism, and the Idealism of Fichte and Hegel (R. J. Richards 2002, 2008, 2013; Gliboff 2007, 2008; Mullen 1964). These factors formed a complex political and philosophical environment into which Darwin’s developmental view of nature and theory of the transformation of species was quickly assimilated, if also altered. Many readings of Darwin consequently interpreted his arguments against the background of Schelling’s philosophy of nature. The marshalling of Darwin’s authority in debates over scientific materialism were also brought to the fore by the enthusiastic advocacy of Darwinism in Germany by University of Jena professor of zoology Ernst Heinrich Haeckel (1834–1919). More than any other individual, Haeckel made Darwinismus a major player in the polarized political and religious disputes of Bismarckian Germany (R. J. Richards 2008). Through his polemical writings, such as the Natural History of Creation (1868), Anthropogeny (1874), and Riddle of the Universe (1895–99), Haeckel advocated a materialist monism in the name of Darwin, and used this as a stick with which to beat traditional religion. Much of the historical conflict between religious communities and evolutionary biology can be traced back to Haeckel’s polemical writings, which went through numerous editions and translations, including several English and American editions that appeared into the early decades of the twentieth century.

To turn to a very different context, that of China, Darwin’s works entered Chinese discussions by a curious route. The initial discussions of Darwinian theory were generated by the translation of Thomas Henry Huxley’s 1893 Romanes Lecture “Evolution and Ethics” by the naval science scholar Yan Fu (1854–1921), who had encountered Darwinism while being educated at the Royal Naval College in Greenwich from 1877 to 1879. This translation of Huxley’s lecture, published in 1898 under the name of Tianyan Lun , was accompanied with an extensive commentary by Yan Fu that drew heavily upon the writings of Herbert Spencer which Yan Fu placed in opposition to the arguments of Huxley. This work has been shown to have been the main vehicle by which the Chinese learned indirectly of Darwin’s theory (Jin 2020, 2019 a, b; Yang 2013; Pusey 1983). In the interpretation of Yan Fu and his allies, such as Kan Yuwei (1858–1927), Darwinism was given a progressivist interpretation in line with aspects of Confucianism.

Beginning in 1902, a second phase of Darwinian reception began with a partial translation of the first five chapters of the sixth edition of the Origin by the Chinese scientist, trained in chemistry and metallurgy in Japan and Germany, Ma Junwu (1881–1940). This partial translation, published between 1902 and 1906, again modified the text itself to agree with the progressive evolutionism of Spencer and with the progressivism already encountered in Yan Fu’s popular Tianyan Lun. Only in September of 1920 did the Chinese have Ma Junwu’s full translation of Darwin’s sixth edition. This late translation presented a more faithful rendering of Darwin’s text, including an accurate translation of Darwin’s final views on natural selection (Jin 2019 a, b). As a political reformer and close associate of democratic reformer Sun Yat-Sen (1866–1925), Ma Junwu’s interest in translating Darwin was also was involved with his interest in revolutionary Chinese politics (Jin 2019a, 2022).

The reception of the Origin by those who held positions of professional research and teaching positions in universities, leadership positions in scientific societies, and employment in museums, was complex. These individuals were typically familiar with the empirical evidence and the technical scientific issues under debate in the 1860s in geology, comparative anatomy, embryology, biogeography, and classification theory. This group can usually be distinguished from lay interpreters who may not have made distinctions between the views of Lamarck, Chambers, Schelling, Spencer, and Darwin on the historical development of life.

If we concentrate attention on the reception by these professionals, Darwin’s work received varied endorsement (Hull 1973). Many prominent members of Darwin’s immediate intellectual circle—Adam Sedgwick, William Whewell, Charles Lyell, Richard Owen, and Thomas Huxley—had previously been highly critical of Chambers’s Vestiges in the 1840s for its speculative character and its scientific incompetence (Secord 2000). Darwin himself feared a similar reception, and he recognized the substantial challenge facing him in convincing this group and the larger community of scientific specialists with which he interacted and corresponded widely. With this group he was only partially successful.

Historical studies have revealed that only rarely did members of the scientific elites accept and develop Darwin’s theories exactly as they were presented in his texts. Statistical studies on the reception by the scientific community in England in the first decade after the publication of the Origin have shown a complicated picture in which there was neither wide-spread conversion of the scientific community to Darwin’s views, nor a clear generational stratification between younger converts and older resisters, counter to Darwin’s own predictions in the final chapter of the Origin (Hull et al. 1978). These studies also reveal a distinct willingness within the scientific community to separate acceptance of Darwin’s more general claim of species descent with modification from common ancestors from the endorsement of his explanation of this descent through the action of natural selection on slight morphological variations.

Of central importance in analyzing this complex professional reception was the role assigned by Darwin to the importance of normal individual variation as the source of evolutionary novelty. As we have seen, Darwin had relied on the novel claim that small individual variations—the kind of differences considered by an earlier tradition as merely “accidental”—formed the raw material upon which, by cumulative directional change under the action of natural selection, major changes could be produced sufficient to explain the origin and subsequent differences in all the various forms of life over time. Darwin, however, left the specific causes of this variation unspecified beyond some effect of the environment on the sexual organs. Variation was presented in the Origin with the statement that “the laws governing inheritance are quite unknown” (Darwin 1859 [1964], 13). In keeping with his commitment to the gradualism of Lyellian geology, Darwin also rejected the role of major “sports” or other sources of discontinuous change in this process.

As critics focused their attacks on the claim that such micro-differences between individuals could be accumulated over time without natural limits, Darwin began a series of modifications and revisions of the theory through a back and forth dialogue with his critics that can be followed in his revisions to the text of the Origin . In the fourth edition of 1866, for example, Darwin inserted the claim that the continuous gradualism depicted by his branching diagram was misleading, and that transformative change does not necessarily go on continuously. “It is far more probable that each form remains for long periods unaltered, and then again undergoes modification” (Darwin 1866, 132; Peckham 2006, 213). This change-stasis-change model allowed variation to stabilize for a period of time around a mean value from which additional change could then resume. Such a model would, however, presumably require even more time for its working than the multi-millions of years assumed in the original presentation of the theory.

The difficulties in Darwin’s arguments that had emerged by 1866 were highlighted in a lengthy and telling critique in 1867 by the Scottish engineer Henry Fleeming Jenkin (1833–1885) (typically Fleeming Jenkin). Using an argument previously raised in the 1830s by Charles Lyell against Lamarck, Fleeming Jenkin cited empirical evidence from domestic breeding that suggested a distinct limitation on the degree to which normal variation could be added upon by selection (Fleeming Jenkin 1867 in Hull 1973). Using a loosely mathematical argument, Fleeming Jenkin argued that the effects of intercrossing would continuously swamp deviations from the mean values of characters and result in a tendency of the variation in a population to return to mean values over time. It is also argued that domestic evidence does not warrant an argument for species change. For Fleeming Jenkin, Darwin’s reliance on continuous additive deviation was presumed to be undermined by these arguments, and only more dramatic and discontinuous change—something Darwin explicitly rejected—could account for the origin of new species.

Fleeming Jenkin also argued that the time needed by Darwin’s theory to account for the history of life under the gradual working of natural selection was simply unavailable from scientific evidence, supporting this claim by an appeal to the physical calculations of the probable age of the solar system presented in publications by his mentor, the Glasgow physicist William Thompson (Lord Kelvin, 1824–1907) (Burchfield 1975). On the basis of Thompson’s quantitative physical arguments concerning the age of the sun and solar system, Fleeming Jenkin judged the time since the presumed first beginnings of life to be insufficient for the Darwinian gradualist theory of species transformation to have taken place.

Jenkin’s multi-pronged argument gave Darwin considerable difficulties and set the stage for more detailed empirical inquiries into variation and its causes by Darwin’s successors. The time difficulties were only resolved in the twentieth-century with the discovery of radioactivity that could explain why the sun did not lose heat in accord with Newtonian principles.

As a solution to the variation question, Darwin developed his “provisional hypothesis” of pangenesis, which he presented the year after the appearance of the Fleeming Jenkin review in his two-volume Variation of Plants and Animals Under Domestication (Darwin 1868; Olby 2013). Although this theory had been formulated independently of the Jenkin review (Olby 1963), in effect it functioned as Darwin’s reply to Jenkin’s critique. The pangenesis theory offered a causal theory of variation and inheritance through a return to a theory resembling Buffon’s theory of the organic molecules proposed in the previous century (see entry on evolutionary thought before Darwin section 3.2). Invisible material “gemmules” were presumed to exist within the cells. According to theory, these were subject to external alteration by the environment and other external causes. The gemmules were then shed continually into the blood stream (the “transport” hypothesis) and assembled by “mutual affinity for each other, leading to their aggregation either into buds or into the sexual elements” (Darwin 1868, vol. 2, 375). In this form they were then transmitted—the details were not explained—by sexual generation to the next generation to form the new organism out of “the modified physiological units of which the organism is built” (ibid., 377). In Darwin’s view, this hypothesis united together numerous issues into a coherent and causal theory of inheritance and explained the basis of variation. It also explained how use-disuse inheritance, a theory which Darwin never abandoned, could work.

The pangenesis theory, although not specifically referred to, seems to be behind an important distinction Darwin inserted into the fifth edition of the Origin of 1869 in his direct reply to the criticisms of Jenkin. In this textual revision, Darwin distinguished “certain variations, which no one would rank as mere individual differences”, from ordinary variations (Darwin1869, 105; Peckham 2006, 178–179). This revision shifted Darwin’s emphasis away from his early reliance on normal slight individual variation, and gave new status to what he now termed “strongly marked” variations. The latter were now the forms of variation to be given primary evolutionary significance. Presumably this strong variation was more likely to be transmitted to the offspring, although details are left unclear, and in this form major variation could presumably be maintained in a population against the tendency to swamping by intercrossing as Fleeming Jenkin had argued.

Darwin’s struggles over this issue defined a set of problems that British life scientists in particular were to deal with into the 1930s. These debates over the role of somatic variation in the evolutionary process placed Darwinism in a defensive posture that forced its supporters into major revisions in the Darwinian research program (Gayon 1998; Vorzimmer 1970). The consequence was a complex period of Darwinian history in which natural selection theory was rejected by many research, or defended in modified form by others (Bowler 1983, 2013a; Largent 2009).

4. Human Evolution and the Descent of Man

Darwin had retained his own conclusions on human evolution quietly in the background through the 1860’s while the defense of his general theory was conducted by advocates as diverse as Thomas Henry Huxley (1825–95) in England, Asa Gray (1810–88) in the United States, and Ernst Haeckel (1834–1919) in the emerging new Germany. Darwin’s own position on the “human question” remained unclear to the reading public, and his rhetorical situating of the Origin within a tradition of divine creation by secondary law, captured in the frontispiece quotations from William Whewell and Francis Bacon, allowed many before 1871 to see Darwin as more open to religious interpretations of human origins than those of some of his popularizers.

Darwin’s interest in developing his insights into the origins of human beings and the explanation of human properties through descent with modification was, however, evident in his correspondence as early as January of 1860 when he began collecting evidence on the expressions of the emotions in human beings (Browne 2002, chp. 9). He then developed a questionnaire specifically intended to gain such information from contacts in Patagonia and Tierra del Fuego (Radick 2018). Further engagement with these issues was then generated by the discussions of Lyell (1863) and A. R. Wallace (1864), both of whom suggested that natural selection could not account for the development of the “higher” rational faculties, language, and ethical motivation (R. J. Richards 1987, chp. 4). It was then in February of 1867 that Darwin decided to remove material from his massive manuscript of the Variation of Plants and Animals Under Domestication to create a “very small volume, ‘an essay on the origin of mankind’” (Darwin to Hooker, 8 February 1867 and CD to Turner, 11 February 1867, Burkhardt, Correspondence 15: 74, 80). At this time he also sent to several international correspondents a more detailed questionnaire asking for information on human emotional expression. Further impetus to develop his views was created by the arguments of William R. Greg (1809–1881) in an essay in Fraser’s Magazine (1868), with further support by arguments of A. R. Wallace in 1869, both of whom drew a sharp distinction between human properties and those of animals (R. J. Richards 1987, 172–184). These arguments denied that natural selection could explain the origins of these “higher powers”.

Darwin’s drafting of his views on human issues, begun in early 1868, expanded into a major enterprise in which he became deeply engaged with the issue of the implications of his theory for ethics. The result of this effort devoted to anthropological topics was two separate works: the Descent of Man and Selection in Relation to Sex , delivered to the publisher in June of 1870 with publication in 1871, and its companion, Expression of the Emotions in Man and Animals , which he commenced in early 1871 with publication in early 1872.

As commentators have noted, these two works differ markedly in their arguments, and reflect different relationships to Darwin’s causal theories of natural and sexual selection, with sexual selection predominting over natural selection for the major portion of the Descent , and both of these causal theories generally missing from the descriptive approach of the Expression (Radick 2018).

Sexual selection—the choosing of females by males or vice versa for breeding purposes—had received a general statement by Darwin in Chapter IV of the Origin , but this played only a minor role in the original argument, and its importance was denied by co-evolutionist A. R. Wallace. In the Descent this was now developed in extensive detail as a major factor in evolution that could even work against ordinary natural selection. Sexual selection could be marshaled to explain sexual dimorphism, and also the presence of unusual characters and properties of organisms—elaborate feeding organs, bright colors, and other seemingly maladaptive structures such as the antlers on the Irish Elk or the great horn on the Rhinoceros beetle—that would appear anomalous outcomes of ordinary natural selection working for the optimal survival of organisms in nature. In a dramatic extension of the principle to human beings, the combination of natural and sexual selection is used to explain the origins of human beings from simian ancestors. It also accounts for the sexual dimorphism in humans, and is a major factor accounting for the origin of human races (E. Richards 2017; R. A. Richards 2013).

Although the secondary causal role of sexual selection in the development of species generally was to be the main topic of the bulk of the Descent , this plays an ambiguous role initially in the “treatise on man” that occupies the initial chapters, and functions differently in his treatment of the origins of mental powers, the moral sense, and the origin of races in this opening discussion.

In constructing this presentation, Darwin reaches back to the early Notebooks that he had separated out from the “transformist” discussions to deal with his inquiries into ethics, psychology, and emotions (see Section 1.2 above). Of particular importance for the opening discussions of the Descent was the “M” notebook, commenced in July of 1838, and “N”, begun in October of that year. On occasion he also samples the collection of entries now entitled “Old and Useless Notes”, generally written between 1838 and 1840.

The initial topic of focus in the Descent deals with the far-reaching issues concerning the status and origin of human mental properties, faculties presumed traditionally to be possessed uniquely by human beings. These properties Darwin now places on an evolutionary continuum with those features of animal behavior long regarded as instinctual. In this he placed himself in opposition to the long tradition of discourse that had distinguished humans from animals due to the possession of a “rational principle” related to their possession of a rational soul. This tradition had been given a more radical foundation in the revolutionary reflections on the relation of mind and body initiated by René Descartes (1596–1650) in the middle of the seventeenth century. Descartes deepened this distinction with the separation of the two substances—thinking substance, or res cogitans , possessed only by humans, and extended material substance, res extensa that constituted the rest of the natural world, including animals and plants, rendering animals only lifeless machines without rational faculties.

Darwin’s collapse of this Cartesian barrier with his theory of human origins outlined in the Descent continued a discussion that had been a concern of his transformist predecessors, especially Jean Baptiste Lamarck (Sloan 1999). But Darwin took this issue to a new level as he interpreted the human-animal relationship in the context of his novel theory of divergent evolution from common ancestors. Darwin also broke with the view of humans as the summit of a natural teleological process. Darwin instead denies such teleological ordering, and effectively reduces human properties to those of animals—mental as well as physical—by tracing them to their origin in properties of lower organisms.

The warrant for the identification of human and animal mental properties, however, is not supported by substantial argumentation in the Descent. The opening discussions of the treatise summarize the anatomical evidence for “homologies” —true identities—between humans and animals due to descent from common ancestors, claims already set out in Chapter Thirteen of the Origin. But the transferal of this identity of structure to inner non-anatomical “mental” properties rested on premises that are not made explicit in this text, and were not identities drawn by Huxley, Wallace and Lyell, for example, in their treatments of humans in relation to evolutionary theory, although they acknowledged the anatomical continuities.

To understand Darwin’s arguments, it is useful to return to his Notebook discussions on which he was drawing for his reasoning (see above, Section 1.2). In his “C” Notebook, opened in February of 1838, Darwin has a remarkable entry that displays very early on his commitment to a metaphysical “monism”—the thesis that there is only one substance underlying both mind and body. With this goes the thesis of a parallelism of the complexity of mental properties with those of material structure. In this entry in “C” following on Darwin’s reflections on the issue of instinct, and also recording some of his observations on animals at the Regents Park zoological gardens, Darwin comments:

There is one living spirit, prevalent over this wor[l]d, (subject to certain contingencies of organic matter & chiefly heat), which assumes a multitude of forms <<each having acting principle>> according to subordinate laws.—There is one thinking […] principle (intimately allied to one kind of organic matter—brain. & which <prin> thinking principle. seems to be given or assumed according to a more extended relations [ sic ] of the individuals, whereby choice with memory, or reason ? is necessary.—) which is modified into endless forms, bearing a close relation in degree & kind to the endless forms of the living beings.— We see thus Unity in thinking and acting principle in the various shades of <dif> separation between those individuals thus endowed, & the community of mind, even in the tendency to delicate emotions between races, & recurrent habits in animals.— (Barrett 1987, 305)

As we follow these issues into the “M” Notebook, the assumption of a single “thinking principle,” allied to one kind of organic matter, seems then to underlie Darwin’s subsequent reflections on mind and matter. The “M” Notebook cites numerous “mental”properties common to humans and animals that generally parallel levels of material organization, similar to the identities expressed in the later Descent. The range of this universal extension of mental properties is far-reaching in these early discussions: consciousness and “free will” extends to all animals, including invertebrates:

With respect to free will, seeing a puppy playing cannot doubt that they have free will, if so all animals., then an oyster has & a polype (& a plant in some senses […]; now free will of oyster, one can fancy to be direct effect of organization, by the capacities its senses give it of pain or pleasure, if so free will is to mind, what chance is to matter […] (Barrett 1987, 536).

When these themes reappear in Chapter Two of the first edition of the Descent , Darwin seems to draw implicitly upon this matter-mind identity theory as an obvious consequence of his theory of descent from common ancestry. There he enumerates a long list of traditional human mental and emotional properties to claim that each of them are identities with the properties of simpler forms of life. The list is expansive: courage, deceit, play, kindness, maternal affection, self-complacency, pride, shame, sense of honor, wonder, dread, imitation, imagination, and dreaming. All are considered to be represented in a wide range of animals, with “play”and “recognition” found even in the ants.

When he addresses the more complex mental properties that specifically had been considered by a long tradition of discussion to be the distinctive human properties—possession of language, reason, abstract conceptual thinking, self-reflection—these again are treated as having their manifestations in other forms of life, with none of them unique to human beings. Language, the property that Descartes, for example, had considered to be the primary distinguishing character denoting the human possession of mind as distinct from matter, Darwin treats a developing in a gradual process from animal sounds that parallel the differentiation of species, illustrated by the fact that languages “like organic beings, can be classed in groups under groups” (Darwin 1871 [1981], 60). He closes his discussion of mental powers with an analysis of religious belief that derives it from imagination and belief in spirits found in aboriginal peoples. It can even be homologized with the “deep love of a dog for his master, associated with complete submissions, some fear, and perhaps other feelings” (ibid., 68). Darwin’s discussions of the relation of human and animal mental and emotional properties would set the agenda for a complex discussion that would carry into contemporary debates over animal cognition and the relations of human and animal properties (see the entries on animal cognition ; methods in comparative cognition ; and animal consciousness ).

The subsequent treatment of ethical issues in the third chapter of the Descent was for Darwin a topic to be approached “exclusively from the side of natural history” (ibid., 71). This issue also presented him with some of his most difficult conceptual problems (CD to Gray, 15 March 1870, Burkhardt, Correspondence 18, 68). In this discussion he also employs natural selection theory as an explanatory cause.

Under the heading of “Moral Sense”, Darwin offered some innovations in ethics that do not easily map on to standard ethical positions classified around the familiar categories of Rule or Act Utilitarianism, Kantian Deontology, Hedonism, and Emotivism. Darwin’s closest historical affinities are with the Scottish “Moral Sense” tradition of Frances Hutcheson (1694–1746), Adam Smith (1723?–1790), and David Hume (1711–1776). More immediately Darwin drew from the expositions of the moral sense theory by his distant relative, Sir James Macintosh (1765–1832) (R. J. Richards 1987, 114–122, 206–219).

Traditional moral sense theory linked ethical behavior to an innate property that was considered to be universal in human beings, although it required education and cultivation to reach its full expression (see the entry on moral sentimentalism ). This inherent property, or “moral” sense, presumably explained such phenomena as ethical conscience, the sense of moral duty, and it accounted for altruistic actions that could not be reduced to hedonic seeking of pleasure and avoiding pain. It also did not involve the rational calculation of advantage, or the maximization of greatest happiness by an individual prior to action, as implied by Utilitarianism. For this reason Darwin criticized John Stuart Mill’s version of Utilitarian theory because it relied on acquired habits and the calculation of advantage (Darwin 1871 [1981], 71n5).

Darwin’s reinterpretation of the moral sense tradition within his evolutionary framework also implied important transfomations of this theory of ethics. The moral sense was not to be distinguished from animal instinct but was instead derived historically from the social instincts and developed by natural selection. From this perspective, Darwin could claim a genuine identity of ethical foundations holding between humans and animals, with the precursors of human ethical behavior found in the behavior of other animals, particularly those with social organization. Natural selection then shaped these ethical instincts in ways that favored group survival over immediate individual benefit (ibid., 98). Human ethical behavior is therefore grounded in a natural property developed by natural selection, with the consequence that ethical actions can occur without moral calculus or rational deliberation.

When moral conflict occurs, this is generally attributed to a conflict of instincts, with the stronger of two conflicting instincts favored by natural selection insofar as it favors group benefit (ibid. 84). In human beings the “more enduring Social Instincts” thus come to override the less persistent “individual” instincts.

The adequacy of evolutionary ethical naturalism as a foundation for ethical realism proved to be a point of contention for Darwin’s contemporaries and successors following the publication of the Descent . For some moral philosophers, Darwin had simply reduced ethics to a property subject to the relativizing tendencies of natural selection (Farber 1994: chp. 5). It was, in the view of Darwin’s philosophical critics, to reduce ethics to biology and in doing so, to offer no way to distinguish ethical goods from survival advantages. Not even for some strong supporters of Darwinism, such as Thomas Huxley and Alfred Russel Wallace, was Darwin’s account adequate (ibid., chp. 4). Much of subsequent development of moral philosophy after Darwin would be grounded upon the canonical acceptance of the “is-ought” distinction, which emerged with new force from the critique of “evolutionary” ethical theory. This critique began with Thomas Huxley’s own break with Darwinian ethical theory in his Romanes Lecture, “Evolution and Ethics”of 1893 (Huxley 1893). This lecture, reflecting Huxley’s views eleven years after Darwin’s death, would play an important role in the Chinese reception of Darwinism (Huxley 1895; see above, section 3.1). This line of critique also received an influential academic expression in G. E. Moore’s (1873–1958) Principia Ethica —itself an attack on Spencer’s version of evolutionary ethics (Moore 1903). Debates over the adequacy of evolutionary ethics continue into the present (see the entries on biological altruism and morality and evolutionary biology ; see also, R. J. Richards 2015, 2009, 1999, 1987, Appendix 2; Charmetant 2013; Boniolo and DeAnna (eds.) 2006; Hauser 2006; Katz (ed.) 2000; Maienschein and Ruse (eds.) 1999).

4.4 Reception of the Descent

The international reception of the Descent of Man and Expression of the Emotions is a topic in need of the kind of detailed studies that surround the historical impact of the Origin. These works presented the reading public after 1871 with a more radical and controversial Darwin than had been associated with the author of the popular Journal of Researches or even the Origin itself, and his anthropological works created a watershed in the public reception of Darwin’s views (Radick 2013). The Descent finally made public Darwin’s more radical conclusions about human origins, and seemed to many of his readers, even those previously sympathetic to the Origin , to throw Darwin’s authority behind materialist and anti-religious forces. Public knowledge of Darwin’s own conclusions on human evolution before 1871 had rested on the one vague sentence on the issue in the Origin itself. The Descent made public his more radical conclusions. Even though the question of human evolution had already been dealt with in part by Thomas Huxley in his Man’s Place in Nature of 1863 (Huxley 1863), and by Charles Lyell in the same year in his Geological Evidences of the Antiquity of Man (Lyell 1863), followed by Alfred Russel Wallace’s articles in 1864 and 1870 (Wallace 1864 and online), these authors had either not dealt with the full range of questions presented by the inclusion of human beings in the evolutionary process, or they had emphasized the moral and mental discontinuity between humans and animals. Only Ernst Heinrich Haeckel had drawn out a more general reductive conception of humanity from evolutionary theory and he had not ventured into the specific issues of ethics, social organization, the origins of human races, and the relation of human mental properties to those of animals, all of which are dealt with in the Descent . Darwin’s treatise presented, as one commentator has put it, “a closer resemblance to Darwin’s early naturalistic vision than anything else he ever published” (Durant 1985, 294).

Darwin’s extension of his theory to a range of questions traditionally discussed within philosophy, theology, and social and political theory, has shaped the more general history of Darwinism since the 1870s. It set the agenda for much of the development of psychology of the late nineteenth century (R. J. Richards 1987). It also hardened the opposition of many religiously-based communities against evolutionary theory, although here again, distinctions must be made between different communities (Ellegård 1990, chp. 14). Such opposition was not simply based upon the denial of the literal scriptural account of the origins of humankind, an issue that played out differently within the main religious denominations (Haught 2013; Finnegan 2013; Swetlitz 2013; Artigas, Glick, & Martinez 2006; Moore 1979). The more fundamental opposition was due to the denial of distinctions, other than those of degree, between fundamental human properties and those of animals.

Furthermore, the apparent denial of some kind of divine guidance in the processes behind human evolution and the non-teleological character of Darwin’s final formulations of the natural selection theory in the fifth and sixth editions of the Origin , hardened this opposition. His adoption from Herbert Spencer of designator “survival of the fittest” as a synonym for “natural selection” in the fifth edition of 1869 added to this growing opposition. As a consequence, the favorable readings that many influential religious thinkers—John Henry Newman (1801–1890) is a good example—had given to the original Origin , disappeared. The rhetoric of the Descent , with its conclusion that “man is descended from a hairy quadruped, furnished with a tail and pointed ears” (Darwin 1871 [1981], 389), presented to the public a different Darwin than many had associated with the popular seagoing naturalist.

The new opposition to Darwin is reflected in the many hostile reviews of the Descent to appear in the periodical press (R. J. Richards 1987, 219–230). Particularly at issue were Darwin’s accounts of the origin of ethical principles and intelletual powers, including language, self-reflection, abstract thinking and religious belief as derivations from animal properties (Anon. 1871)

The profound revolution in thought that Darwin created, however, was eventually recognized even by his one-time harsh critics. The once leading British comparative anatomist Richard Owen (1804–1892), who had long been estranged from Darwin since his harsh review of the Origin in 1860, nonetheless could comment on the occasion of Darwin’s burial in Westminster Abbey in a letter to Horace Walpole:

The great value of Darwin’s series of works, summarizing all the evidence of Embryology, Paleontology, & Physiology experimentally applied in producing Varieties of Species, is exemplified in the general acceptance by Biologists of the Secondary Law, by Evolution, of the ‘Origin of Species’ […] In this respect Charles Darwin stands to Biology in the relation which Copernicus stood to Astronomy. […] [Copernicus] knew not how the planets revolved around the sun. To know that required the successive labours of a Galileo, a Kepler and finally a Newton […] Meanwhile our British Copernicus of Biology merits the honour and the gratitude of the Empire, which is manifest by a Statue in Westminster Abbey. (Richard Owen to Horace Walpole, 5 November, 1882, Royal College of Surgeons of England Archives, MS0025/1/5/4).

The subsequent history of the debates surrounding Darwin’s achievement forms a complex story that involves much of the history of life science, as well as ethical theory, psychology, philosophy, theology and social theory since 1870. For a general summary of recent scholarship see Ruse 2013a and articles from this encyclopedia listed below.

This article has intended to give a historical overview of the specific nature of Darwinian theory, and outline the ways in which it differed from the theories of predecessors in the nineteenth century (see the entry evolution before Darwin ). The eventual general consensus achieved by the middle of the twentieth century around the so-named “Synthetic” theory of evolution that would combine population genetics with a mathematical analysis of evolutionary change, has formed a successful research program for more than half a century (Smocovitis 1996; Mayr and Provine 1980; Provine 1971). This “synthesis” has been challenged in recent decades by the current movement known as evolutionary developmental theory, or “evo-devo”. This development represents in some important respects a return to presumably discarded traditions and lines of exploration of the nineteenth and early twentieth centuries which sought to link evolution with embryological development, and to a complex understanding of genetics, with re-examination of the effects of external conditions on inheritance (Gilbert 2015; Newman 2015; Laubichler and Maienschein 2007; Gissis and Jablonka 2011; Pigliucci and Müller 2010; Amundson 2005; Gilbert, Opitz and Raff 1996). Where these debates and revisions in evolutionary theory may lead in another fifty years is a matter of speculation (Gayon 2015 in Sloan, McKenny and Eggleson 2015).

More general philosophical issues associated with evolutionary theory—those surrounding natural teleology, ethics, the relation of evolutionary naturalism to the claims of religious traditions, the implications for the relation of human beings to the rest of the organic world—continue as issues of scholarly inquiry. The status of Darwin’s accounts of human mental powers and moral properties continue to be issues of philosophical debate. The adequacy of his reliance on sexual selection to explain sex and gender roles in human society form heated topics in some feminist scholarship. Such developments suggest that there are still substantial theoretical issues at stake that may alter the future understanding of evolutionary theory in important ways (Sloan, McKenny, & Eggleson [eds] 2015).

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How to cite this entry . Preview the PDF version of this entry at the Friends of the SEP Society . Look up topics and thinkers related to this entry at the Internet Philosophy Ontology Project (InPhO). Enhanced bibliography for this entry at PhilPapers , with links to its database.

• The Complete Works of Charles Darwin Online , maintained by John van Wyhe, Cambridge University Library. In particular note the Darwin Papers & Manuscripts section
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adaptationism | altruism | altruism: biological | animal: cognition | animal: consciousness | biology: philosophy of | comparative cognition, methods in | creationism | Darwinism | evolution: concept before Darwin | evolution: cultural | fitness | genetics: ecological | life | morality: and evolutionary biology | moral sentimentalism | natural selection | natural selection: units and levels of | Newton, Isaac: philosophy | species | Spencer, Herbert | teleology: teleological notions in biology | Whewell, William

The author wishes to acknowledge the valuable comments on this version of the article by David Depew, Gregory Radick, M. J. S. Hodge, Alan Love, and Xiaoxing Jin. Additional comments were made on an earlier version by Michael Ruse, Robert J. Richards, Edward Zalta, M. Katherine Tillman, and the anonymous reviewers for the Stanford Encyclopedia of Philosophy. I am particularly indebted to Dr. Xiaoxing Jin for information contained in his substantial doctoral work and subsequent research on the reception of Darwinism into China. Responsibility for all interpretations is my own.

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• Genet Mol Biol
• v.42(1); Jan-Mar 2019

Science and evolution

Claudia a.m. russo.

1 Universidade Federal do Rio de Janeiro, Universidade Federal do Rio de Janeiro, Departamento de Genética, Rio de Janeiro RJ , Brazil, Departamento de Genética, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil

Thiago André

2 Universidade Federal do Oeste do Pará, Universidade Federal do Oeste do Pará, Programa de Pós-Graduação em Biodiversidade, Santarém PA , Brazil, Programa de Pós-Graduação em Biodiversidade, Universidade Federal do Oeste do Pará, Santarém, PA, Brazil

Evolution is both a fact and a theory. Evolution is widely observable in laboratory and natural populations as they change over time. The fact that we need annual flu vaccines is one example of observable evolution. At the same time, evolutionary theory explains more than observations, as the succession on the fossil record. Hence, evolution is also the scientific theory that embodies biology, including all organisms and their characteristics. In this paper, we emphasize why evolution is the most important theory in biology. Evolution explains every biological detail, similar to how history explains many aspects of a current political situation. Only evolution explains the patterns observed in the fossil record. Examples include the succession in the fossil record; we cannot find the easily fossilized mammals before 300 million years ago; after the extinction of the dinosaurs, the fossil record indicates that mammals and birds radiated throughout the planet. Additionally, the fact that we are able to construct fairly consistent phylogenetic trees using distinct genetic markers in the genome is only explained by evolutionary theory. Finally, we show that the processes that drive evolution, both on short and long time scales, are observable facts.

In recent years, the teaching of creationism within science curricula has become a subject of public debate worldwide ( Miller et al. , 2006 ; Reiss 2011 ). Most of the attention has been given to cases in the United States of America ( Jackson et al. , 1995 ; Berkman and Plutzer, 2011 ; Baltzley, 2016 ; Ross, 2017 ), where many bills have been submitted to the Houses of Representatives encouraging teachers to express their criticism about evolution. In more serious cases, such as Turkey, evolution has recently been removed from the high school curriculum ( Kingsley, 2017 ), and in Brazil, intelligent design research has recently reached university level ( Silva, 2017 ). The rise of “anti-vaxxers” and “flat-earthers” openly demonstrates that the anti-science movement is not confined to biology, with devastating consequences such as the vaccine-preventable outbreaks ( Miller et al. , 2015 ). At the same time, the anti-science debates have been usually promoted by anti-scientists and have stayed marginal to scientific literature. This explains the rising trend and confirms the need for scientists to hastily step into the scene. With this in mind, we felt compelled to address basic aspects of science and of the scientific method in the evolution versus divine creation debate in a scientific journal.

Science can be defined as being both the criterion for gathering scientific data (scientific method), as well as the explanatory theories that were developed following its criteria (scientific knowledge) ( Project 2061 American Association for the Advancement of Science, 1993 ; Roberts 2007 ). A few centuries ago, scientists decided to select a small part of human knowledge to restrict the method used to assemble this knowledge. The use of the scientific method does not mean that this is more valuable than other types of knowledge; it is just more reliable in uncovering natural laws ( Atkins, 1995 ).

One should regard science as a process in which scientists formulate hypotheses to explain certain facts and to test their predictive models by confronting their predictions with new facts ( Gilbert, 1991 ). A fact is something that we observe. For instance, when we drop an object, it falls to the ground. This is a fact. The scientific theory that explains why objects fall is the theory of gravity . A valid scientific theory can never become a fact ( Gould, 1981 ), as there is always the possibility that a future explanation will better match newly discovered facts.

Evolution as a fact and theory

Evolution is a population concept. An individual does not evolve; only populations evolve in the face of the genetic changes accumulated from one generation to the next. The flu virus evolves. This explains why last years’ flu vaccine does not work on the current strain of the virus: only the resistant strains of the virus survived last year’s vaccine application. This is a textbook example of evolution by natural selection. Genetic modifications are encountered in the resistant strains; thus, evolution is a fact ( Gould, 1981 ). Mutation, migration, natural selection, and genetic drift are the evolutionary forces that drive genetic changes of natural populations from one generation to the next. This is known among biologists as microevolution.

On the other hand, evolutionary theory explains more than those facts that we can routinely observe. This makes it a theory, but is it just a theory? The word theory has distinct meanings in science and in lay language ( Ghose, 2013 ). A scientific theory is the utmost position an idea may reach in science. Outside of academia, however, a theory is equivalent to a hypothesis, an idea that explains facts but has never been tested ( Futuyama and Kirkpatrick, 2017 ). This occurs because there seems to be no need for a distinction between hypothesis and theory outside the scope of science. In science, however, this distinction is fundamental. An idea remains a hypothesis if it has never been confronted with new (independently collected) scientific data that would serve as a test for its predictions. If a hypothesis has endured further testing by subsequent scientific experiments, in time it becomes a valid scientific theory ( Figure 1 ).

For any given valid scientific theory there are three possibilities. The first possibility is that the true explanation for the facts is entirely different from the valid scientific theory. In this case, all scientific experiments aimed to test the theory were flawed in design or in the interpretation of the results. The second possibility is that the true explanation for the facts is more restricted than the current scientific theory claims. In this case, the predictions of the theory agreed with newly collected data because all tests focused on a single (and true ) aspect of the theory. Finally, the last alternative is that the true explanation for the facts is the scientific theory. Science has the tools to reject (first alternative) and to refine (second alternative) scientific theories when they are confronted with new data. However, even theories that endure many tests must still face these three possibilities, as, even in light of the true explanation, science does not furnish us the tools to perceive truthfulness.

A hallmark of natural sciences is that scientific hypotheses and scientific theories must make predictions about the natural world ( Paz-y-Miño and Spinosa, 2011 ). Often, the older the theory, the more reliable it is because it has survived many empirical tests. Furthermore, the more universal the theory, the more robust it becomes with time, as more tests would have been performed. According to Darwin, evolutionary theory is centred around two points ( Darwin, 1859 ). First, from one generation to the next, natural populations change over time by a process of natural selection. Second, all organisms have a common ancestor, and the time since this last common ancestor lived is inversely proportional to the similarities that the organisms will share today. Hence, evolutionary theory is universal because it includes all (living and fossil) biological diversity and has implications for all heritable characteristics of life. Since 1859, evolutionary theory has become the most universal and, hence, widely tested of the scientific theories in biology.

Today, Darwin’s original theory has been refined, as he himself anticipated that it would be ( Darwin, 1871 ). This occurred in many fronts because recent concepts, such as genetic drift and mutations, have provided more details on how natural populations evolve. One example is the understanding that, at the molecular level, random evolution, rather than natural selection, plays the most important role ( Kimura, 1991 ). This is known as the neutral theory, which completed its 50 th anniversary in 2018.

The substance of Darwin’s original theory, however, remains. Theodosius Dobzhansky (1973) shared his astonishment that Charles Darwin proposed the theory of evolution without many key biological concepts, such as that DNA is the molecule responsible for heredity. Half a century after Dobzhansky’s paper, it remains impressive that the theory of evolution still stands valid in light of the discoveries of the molecular biology revolution. Each newly sequenced genome tests some aspects of Darwin’s theory, and, on each case, the sequence has been consistent with Darwin’s prediction of the shared evolutionary history of life. The sharp increase in scope and universality of evolution has strengthened Darwin’s original proposal and made evolutionary theory one of the most reliable and tested theories in the natural sciences ( National Academy of Sciences, 2008 ).

Some creationists dispute this information, claiming that scientists discredit data that go against evolutionary theory. Nonetheless, there is no room for considering worldwide, long-lasting conspiracies in science, as scientific fame and recognition come from the demolition of old theories, not from adherence to them ( Atkins, 1995 ). Indeed, scientists themselves have challenged many aspects of the original Darwinian theory of evolution, such as the importance of neutral evolution, the discovery of epigenetics, the proposal of punctuated equilibrium, etc. When these challenges were first proposed, they were not ignored; they were published in top scientific journals and have been subject to meticulous research and have generated fruitful debates in the scientific arena.

Furthermore, if scientists were dishonestly accepting a false theory of evolution, Lamarck’s theory of inheritance of acquired characters would still be considered valid today. However, it is not. In the XIX century, August Weissman (1889) removed the tails of 20 generations of mice, but no significant decrease in length was found in the descendants’ tails. Scientists themselves devised the scientific experiment that bluntly rejected Lamarck’s proposal as a mechanism of evolution ( Dobzhansky, 1973 ). Scientists do not discredit data that goes against evolution; otherwise, Lamarck’s idea would still be accepted. They discredit scientific untestable theories and explanations that were not gathered using the scientific method.

The cornerstone of biology

Just as human history explains the geopolitical configurations of our world today, modern biological systems are a direct result of their evolutionary past. Hence, evolutionary theory is the cornerstone of the discipline of biology ( Rutledge and Warden, 2000 ). The discipline of biology today is an instantaneous portrayal of the dynamic evolutionary axis that arose with the origin of life and has been changing by evolution ever since ( Figure 2 ). With the first life, genetics, ecology, biochemistry and evolution began.

As a scientific theory, however, which facts does evolutionary theory explain? One pivotal example is the succession in the fossil record. This evolution, namely, macroevolution, explains the larger evolutionary picture that is the appearance of the greater groups, such as the evolution of mammals, insects, and plants. Fossilized mammals are easily recognized, as they have distinct types of teeth, such as molars, canines, and incisors. These vertebrates are also very likely to fossilize on account of their rigid teeth and hard cranium. If mammals are so easily fossilized, how can we explain a rich fossil record full of vertebrates and invertebrates with no mammalian fossil before 300 million years ago?

Similarly, if we dig deeper still, disclosing 500 million years old layers, we find no hard skeleton vertebrates but plenty of fossilized invertebrates in a boost of diversity that we call the Cambrian Explosion. There are no vertebrates in this explosion because vertebrates appear in a much later explosion. Digging even deeper, to 600 million years old records, we find strata with soft-bodied Ediacaran animals but no hard-shelled invertebrates and no vertebrates. In one billion years old strata, we find only single-celled organisms.

How can we find, in old strata, many single celled organisms but not a single mammalian tooth? The only reasonable explanation for these facts is that 400 million years ago, mammals had not yet evolved; 500 million years ago, vertebrates had not yet evolved; 600 million years ago, hard-shelled invertebrates had not yet evolved; and one billion years ago, multicellular life had not yet evolved. Smaller local successions are also observable in the fossil record; such as the beautiful strings of intermediate fossils that include amphibians ( Kustchera and Elliot, 2013 ), birds, whales ( Thewissen, 2009 ), horses, and humans. These successions in the fossil record are the most obvious evidence to macroevolution ( Figure 2 ). In fact, the entire fossil record is a set of millions of intermediate fossils that provide solid evidence of how macroevolution worked in the past billion years.

Evolutionary processes that drive micro and macroevolution are facts

To have a better understanding of evolution, we must discuss the processes that drive evolution. For this, we start by comparing processes that drive microevolution with those that drive macroevolution. Many of the same evolutionary processes that drive microevolution also drive macroevolution, namely natural selection, mutation, migration, and genetic drift. A lineage will tend to diversify if it has adaptations that increase survival and reproductive abilities compared to other species. This advantage will tend to increase population size and the geographical distribution of the ancestral species that will more likely speciate into two descendant species. Hence, according to this view, macroevolution is microevolution on a larger scale ( Zimmer, 2001 ), with biological speciation as the only additional process ( Russo et al. , 2016 ). Through speciation, one ancestral species gives rise to two descendant species that are reproductively incompatible with each other.

More than a million species have been described ( Mora et al. , 2011 ), and each biological species includes many interbreeding members. Also, most species are reproductively isolated from each other. The fact that we observe biological species with interbreeding members and reproductive isolation between species is compatible with both separate creation and macroevolution. So, which observable pattern would we expect if many speciation events generated the vast biological diversity from a single common ancestor? In this case, we would expect different degrees of similarity between reproductively isolated species. This is exactly what we observe. Some species are very similar, such as chimpanzees and gorillas, with most features shared between them. Other species, on the other hand, are morphologically so different that one must look into cytology, physiology, or comparative genomics to detect evidence of their common past. One example is a fern and a frog. For instance, the cellular respiration is a process shared by ferns and frogs and it is an evidence of their common ancestry. Only macroevolution explains well the distinct degrees of similarity between these four isolated species, as the age of their last common ancestor is inversely proportional to the similarity between any two species.

Furthermore, the existence of hybrids, such as the mule, the liger, the coywolf, is also only explained by the hierarchical common ancestry theory, not by separate creation. The hybrids are direct evidence of on-going processes of speciation. Thus, the presence of hybrids is what we would expect if all life had a common ancestry.

Other fossil record patterns are well explained by macroevolution. For instance, why do we find a major increase in mammalian fossil diversity only after the disappearance of non-avian dinosaurs approximately 65 million years ago? The same pattern is observed in the fossil record of birds. Macroevolution explains this well, as the extinction of dinosaurs eliminated competition, and the surviving ancestral mammals were able to increase in number and diversified through speciation, generating more species of their kind.

Final remarks

A single, very well designed experiment, performed in accordance with the utmost scientific standards, is what it takes to put any scientific theory to rest. Divine creation will never be part of science because science is not able to detect supernatural phenomena. Divine phenomena explain everything equally; hence, it provides no real explanatory (i.e., predictive) power. If we accept “God’s will” as an adequate explanation for a natural phenomenon, we eliminate the possibility of eventually being able to explain it naturally. Thus, the scientific revolution begun when we eliminated the divine as a scientific explanation.

Science, as a process, starts with the acceptance of our ignorance about a natural phenomenon and by seeking natural explanations for it. Hence, ignorance drives the engine of Science. Even if evolution were, hypothetically, rejected, contested by new data, scientists would have to study hard to find an alternative natural explanation that was able to explain everything that evolution explains today plus the new data that contested it.

Evolution is a fact and a well-supported scientific theory. It has endured daily and rigorous testing, and it stands as the unifying theory in biology ( Rutledge and Warden, 2000 ). This says nothing about whether God created or did not create the world, as science is unable to distinguish a divinely guided evolution from a materialistic evolution. God may well have created the biological world through natural selection, mutation, speciation, extinction, etc. Still, evolution and Science would remain unscathed as Science is not concerned with why or who , but only with how .

Some creationists say that we must bring the evolution versus creationist debate to the classroom and claim that the opposition to the debate is anti-scientific. However, science is not about blind criticism ( Meyer and El-Hani, 2013 ). Blind criticism is just as naïve as blind acceptance. Scientists must weigh the evidence before questioning a theory. The idea that all debates are equally scientific is misleading and it explains the sad emergence of flat-earthers and anti-vaxxers. A debate on what is the shape of our planet is not only pointless, but it is also dangerously harmful to the minds of the young students. A fruitful debate in a science class is restricted to those issues that lie within the scientific realm ( Baltzley, 2016 , Branch, 2016 ).

A recent study has suggested that science concepts, more than evolutionary basics, are critical to promoting evolution ( Dunk et al. , 2017 ). One way to reinforce these fundamentals would be the requirement of evolution and science fundaments in admission policies for biology professionals, particularly teachers ( Larkin and Perry-Ryder, 2015 ; see Rutledge and Warden, 2000 for statistics).

Associate Editor: Carlos F. M. Menck

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18.1 Understanding Evolution

Learning objectives.

By the end of this section, you will be able to do the following:

• Describe how scientists developed the present-day theory of evolution
• Define adaptation
• Explain convergent and divergent evolution
• Describe homologous and vestigial structures
• Discuss misconceptions about the theory of evolution

Evolution by natural selection describes a mechanism for how species change over time. Scientists, philosophers, researchers, and others had made suggestions and debated this topic well before Darwin began to explore this idea. Classical Greek philosopher Plato emphasized in his writings that species were static and unchanging, yet there were also ancient Greeks who expressed evolutionary ideas. In the eighteenth century, naturalist Georges-Louis Leclerc Comte de Buffon reintroduced ideas about the evolution of animals and observed that various geographic regions have different plant and animal populations, even when the environments are similar. Some at this time also accepted that there were extinct species.

Also during the eighteenth century, James Hutton, a Scottish geologist and naturalist, proposed that geological change occurred gradually by accumulating small changes from processes operating like they are today over long periods of time. This contrasted with the predominant view that the planet's geology was a consequence of catastrophic events occurring during a relatively brief past. Nineteenth century geologist Charles Lyell popularized Hutton's view. A friend to Darwin. Lyell’s ideas were influential on Darwin’s thinking: Lyell’s notion of the greater age of Earth gave more time for gradual change in species, and the process of change provided an analogy for this change. In the early nineteenth century, Jean-Baptiste Lamarck published a book that detailed a mechanism for evolutionary change. We now refer to this mechanism as an inheritance of acquired characteristics by which the environment causes modifications in an individual, or offspring could use or disuse of a structure during its lifetime, and thus bring about change in a species. While many discredited this mechanism for evolutionary change, Lamarck’s ideas were an important influence on evolutionary thought.

Charles Darwin and Natural Selection

In the mid-nineteenth century, two naturalists, Charles Darwin and Alfred Russel Wallace, independently conceived and described the actual mechanism for evolution. Importantly, each naturalist spent time exploring the natural world on expeditions to the tropics. From 1831 to 1836, Darwin traveled around the world on H.M.S. Beagle , including stops in South America, Australia, and the southern tip of Africa. Wallace traveled to Brazil to collect insects in the Amazon rainforest from 1848 to 1852 and to the Malay Archipelago from 1854 to 1862. Darwin’s journey, like Wallace’s later journeys to the Malay Archipelago, included stops at several island chains, the last being the Galápagos Islands west of Ecuador. On these islands, Darwin observed species of organisms on different islands that were clearly similar, yet had distinct differences. For example, the ground finches inhabiting the Galápagos Islands comprised several species with a unique beak shape ( Figure 18.2 ). The species on the islands had a graded series of beak sizes and shapes with very small differences between the most similar. He observed that these finches closely resembled another finch species on the South American mainland. Darwin imagined that the island species might be species modified from one of the original mainland species. Upon further study, he realized that each finch's varied beaks helped the birds acquire a specific type of food. For example, seed-eating finches had stronger, thicker beaks for breaking seeds, and insect-eating finches had spear-like beaks for stabbing their prey.

Wallace and Darwin both observed similar patterns in other organisms and they independently developed the same explanation for how and why such changes could take place. Darwin called this mechanism natural selection. Natural selection , or “survival of the fittest,” is the more prolific reproduction of individuals with favorable traits that survive environmental change because of those traits. This leads to evolutionary change.

For example, Darwin observed a population of giant tortoises in the Galápagos Archipelago to have longer necks than those that lived on other islands with dry lowlands. These tortoises were “selected” because they could reach more leaves and access more food than those with short necks. In times of drought when fewer leaves would be available, those that could reach more leaves had a better chance to eat and survive than those that couldn’t reach the food source. Consequently, long-necked tortoises would be more likely to be reproductively successful and pass the long-necked trait to their offspring. Over time, only long-necked tortoises would be present in the population.

Natural selection, Darwin argued, was an inevitable outcome of three principles that operated in nature. First, most characteristics of organisms are inherited, or passed from parent to offspring. Although no one, including Darwin and Wallace, knew how this happened at the time, it was a common understanding. Second, more offspring are produced than are able to survive, so resources for survival and reproduction are limited. The capacity for reproduction in all organisms outstrips the availability of resources to support their numbers. Thus, there is competition for those resources in each generation. Both Darwin and Wallace’s understanding of this principle came from reading economist Thomas Malthus' essay that explained this principle in relation to human populations. Third, offspring vary among each other in regard to their characteristics and those variations are inherited. Darwin and Wallace reasoned that offspring with inherited characteristics which allow them to best compete for limited resources will survive and have more offspring than those individuals with variations that are less able to compete. Because characteristics are inherited, these traits will be better represented in the next generation. This will lead to change in populations over generations in a process that Darwin called descent with modification. Ultimately, natural selection leads to greater adaptation of the population to its local environment. It is the only mechanism known for adaptive evolution.

In 1858, Darwin and Wallace ( Figure 18.3 ) presented papers at the Linnean Society in London that discussed the idea of natural selection. The following year Darwin’s book, On the Origin of Species, was published. His book outlined in considerable detail his arguments for evolution by natural selection.

Studies of evolution by natural selection are difficult to conduct, as they require analyses of several generations of the investigated species in order to document the changes pointing to evolutionary change. The Galápagos finches are an excellent example. Peter and Rosemary Grant and their colleagues have studied Galápagos finch populations every year since 1976 and have provided important evidence of natural selection. The Grants found changes from one generation to the next in beak shape distribution with the medium ground finch on the Galápagos island of Daphne Major. The birds have inherited a variation in their bill shape with some having wide deep bills and others having thinner bills. During a period in which rainfall was higher than normal because of an El Niño, there was a lack of large hard seeds of which the large-billed birds ate; however, there was an abundance of the small soft seeds which the small-billed birds ate. Therefore, the small-billed birds were able to survive and reproduce. In the years following this El Niño, the Grants measured beak sizes in the population and found that the average bill size was smaller. Since bill size is an inherited trait, parents with smaller bills had more offspring and the bill evolved into a much smaller size. As conditions improved in 1987 and larger seeds became more available, the trend toward smaller average bill size ceased.

Career Connection

Field biologist.

Many people hike, explore caves, scuba dive, or climb mountains for recreation. People often participate in these activities hoping to see wildlife. Experiencing the outdoors can be incredibly enjoyable and invigorating. What if your job entailed working in the wilderness? Field biologists by definition work outdoors in the “field.” The term field in this case refers to any location outdoors, even under water. A field biologist typically focuses research on a certain species, group of organisms, or a single habitat ( Figure 18.4 ).

One objective of many field biologists includes discovering new, unrecorded species. Not only do such findings expand our understanding of the natural world, but they also lead to important innovations in fields such as medicine and agriculture. Plant and microbial species, in particular, can reveal new medicinal and nutritive knowledge. Other organisms can play key roles in ecosystems or if rare require protection. When discovered, researchers can use these important species as evidence for environmental regulations and laws.

Processes and Patterns of Evolution

Natural selection can only take place if there is variation , or differences, among individuals in a population. Importantly, these differences must have some genetic basis; otherwise, the selection will not lead to change in the next generation. This is critical because nongenetic reasons can cause variation among individuals such as an individual's height because of better nutrition rather than different genes.

Genetic diversity in a population comes from two main mechanisms: mutation and sexual reproduction. Mutation, a change in DNA, is the ultimate source of new alleles, or new genetic variation in any population. The genetic changes that mutation causes can have one of three outcomes on the phenotype. A mutation affects the organism's phenotype in a way that gives it reduced fitness—lower likelihood of survival or fewer offspring. A mutation may produce a phenotype with a beneficial effect on fitness. Many mutations will also have no effect on the phenotype's fitness. We call these neutral mutations. Mutations may also have a whole range of effect sizes on the organism's fitness that expresses them in their phenotype, from a small effect to a great effect. Sexual reproduction also leads to genetic diversity: when two parents reproduce, unique combinations of alleles assemble to produce the unique genotypes and thus phenotypes in each offspring.

We call a heritable trait that helps an organism's survival and reproduction in its present environment an adaptation . Scientists describe groups of organisms adapting to their environment when a genetic variation occurs over time that increases or maintains the population's “fit” to its environment. A platypus's webbed feet are an adaptation for swimming. A snow leopard's thick fur is an adaptation for living in the cold. A cheetah's fast speed is an adaptation for catching prey.

Whether or not a trait is favorable depends on the current environmental conditions. The same traits are not always selected because environmental conditions can change. For example, consider a plant species that grew in a moist climate and did not need to conserve water. Large leaves were selected because they allowed the plant to obtain more energy from the sun. Large leaves require more water to maintain than small leaves, and the moist environment provided favorable conditions to support large leaves. After thousands of years, the climate changed, and the area no longer had excess water. The direction of natural selection shifted so that plants with small leaves were selected because those populations were able to conserve water to survive the new environmental conditions.

The evolution of species has resulted in enormous variation in form and function. Sometimes, evolution gives rise to groups of organisms that become tremendously different from each other. We call two species that evolve in diverse directions from a common point divergent evolution . We can see such divergent evolution in the forms of the reproductive organs of flowering plants which share the same basic anatomies; however, they can look very different as a result of selection in different physical environments and adaptation to different kinds of pollinators ( Figure 18.5 ).

In other cases, similar phenotypes evolve independently in distantly related species. For example, flight has evolved in both bats and insects, and they both have structures we refer to as wings, which are adaptations to flight. However, bat and insect wings have evolved from very different original structures. We call this phenomenon convergent evolution , where similar traits evolve independently in species that do not share a recent common ancestry. The trait in the two species came to be similar in structure and have the same function, flying, but did so separately from each other.

These physical changes occur over enormous time spans and help explain how evolution occurs. Natural selection acts on individual organisms, which can then shape an entire species. Although natural selection may work in a single generation on an individual, it can take thousands or even millions of years for an entire species' genotype to evolve. It is over these large time spans that life on earth has changed and continues to change.

Evidence of Evolution

The evidence for evolution is compelling and extensive. Looking at every level of organization in living systems, biologists see the signature of past and present evolution. Darwin dedicated a large portion of his book, On the Origin of Species , to identifying patterns in nature that were consistent with evolution, and since Darwin, our understanding has become clearer and broader.

Fossils provide solid evidence that organisms from the past are not the same as those today, and fossils show the gradual evolutionary changes over time. Scientists determine the age of fossils and categorize them from all over the world to determine when the organisms lived relative to each other. The resulting fossil record tells the story of the past and shows the evolution of form over millions of years ( Figure 18.6 ). For example, scientists have recovered highly detailed records showing the evolution of humans and horses ( Figure 18.6 ). The whale flipper shares a similar morphology to bird and mammal appendages ( Figure 18.7 ) indicating that these species share a common ancestor.

Anatomy and Embryology

Another type of evidence for evolution is the presence of structures in organisms that share the same basic form. For example, the bones in human, dog, bird, and whale appendages all share the same overall construction ( Figure 18.7 ) resulting from their origin in a common ancestor's appendages. Over time, evolution led to changes in the bones' shapes and sizes in different species, but they have maintained the same overall layout. Scientists call these synonymous parts homologous structures .

Some structures exist in organisms that have no apparent function at all, and appear to be residual parts from a past common ancestor. We call these unused structures without function vestigial structures . Other examples of vestigial structures are wings on flightless birds, leaves on some cacti, and hind leg bones in whales. Not all similarities represent homologous structures. As explained in Determining Evolutionary Relationships , when similar characteristics occur because of environmental constraints and not due to a close evolutionary relationship, it is an analogy or homoplasy. For example, insects use wings to fly like bats and birds, but the wing structure and embryonic origin are completely different. These are analogous structures ( Figure 20.8 ). On the other side, the bird and bat wings are homologous because the bones are inherited from a common ancestor, while the wings themselves are analogous as they evolved independently.

Link to Learning

Watch this video exploring the bones in the human body.

Another piece of evidence of evolution is the convergence of form in organisms that share similar environments. For example, species of unrelated animals, such as the arctic fox and ptarmigan, living in the arctic region have been selected for seasonal white phenotypes during winter to blend with the snow and ice ( Figure 18.8 ). These similarities occur not because of common ancestry, but because of similar selection pressures—the benefits of predators not seeing them.

Embryology, the study of the anatomy of an organism's development to its adult form, also provides evidence of relatedness between now widely divergent groups of organisms. Mutational tweaking in the embryo can have such magnified consequences in the adult that tends to conserve embryo formation. As a result, structures that are absent in some groups often appear in their embryonic forms and disappear when they reach the adult or juvenile form. For example, all vertebrate embryos, including humans, exhibit gill slits and tails at some point in their early development. These disappear in the adults of terrestrial groups but adult forms of aquatic groups such as fish and some amphibians maintain them. Great ape embryos, including humans, have a tail structure during their development that they lose when they are born.

Biogeography

The geographic distribution of organisms on the planet follows patterns that we can explain best by evolution in conjunction with tectonic plate movement over geological time. Broad groups that evolved before the supercontinent Pangaea broke up (about 200 million years ago) are distributed worldwide. Groups that evolved since the breakup appear uniquely in regions of the planet, such as the unique flora and fauna of northern continents that formed from the supercontinent Laurasia and of the southern continents that formed from the supercontinent Gondwana. The presence of members of the plant family Proteaceae in Australia, southern Africa, and South America was most predominant prior to the southern supercontinent Gondwana breaking up.

Marsupial diversification in Australia and the absence of other mammals reflect Australia’s long isolation. Australia has an abundance of endemic species—species found nowhere else—which is typical of islands whose isolation by expanses of water prevents species from migrating. Over time, these species diverge evolutionarily into new species that look very different from their ancestors that may exist on the mainland. Australia's marsupials, the Galápagos' finches, and many species on the Hawaiian Islands are all unique to their one point of origin, yet they display distant relationships to ancestral species on mainlands.

Molecular Biology

Like anatomical structures, the molecular structures of life reflect descent with modification. DNA's universality reflects evidence of a common ancestor for all of life. Fundamental divisions in life between the genetic code, DNA replication, and expression are reflected in major structural differences in otherwise conservative structures such as ribosome components and membrane structures. In general, the relatedness of groups of organisms is reflected in the similarity of their DNA sequences—exactly the pattern that we would expect from descent and diversification from a common ancestor.

DNA sequences have also shed light on some of the mechanisms of evolution. For example, it is clear that the evolution of new functions for proteins commonly occurs after gene duplication events that allow freely modifying one copy by mutation, selection, or drift (changes in a population’s gene pool resulting from chance), while the second copy continues to produce a functional protein.

Misconceptions of Evolution

Although the theory of evolution generated some controversy when Darwin first proposed it, biologists almost universally accepted it, particularly younger biologists, within 20 years after publication of On the Origin of Species . Nevertheless, the theory of evolution is a difficult concept and misconceptions about how it works abound.

This site addresses some of the main misconceptions associated with the theory of evolution.

Evolution Is Just a Theory

Critics of the theory of evolution dismiss its importance by purposefully confounding the everyday usage of the word “theory” with the way scientists use the word. In science, we understand a “theory” to be a body of thoroughly tested and verified explanations for a set of observations of the natural world. Scientists have a theory of the atom, a theory of gravity, and the theory of relativity, each which describes understood facts about the world. In the same way, the theory of evolution describes facts about the living world. As such, a theory in science has survived significant efforts to discredit it by scientists. In contrast, a “theory” in common vernacular is a word meaning a guess or suggested explanation. This meaning is more akin to the scientific concept of “hypothesis.” When critics of evolution say it is “just a theory,” they are implying that there is little evidence supporting it and that it is still in the process of rigorous testing. This is a mischaracterization.

Individuals Evolve

Evolution is the change in a population's genetic composition over time, specifically over generations, resulting from differential reproduction of individuals with certain alleles. Individuals do change over their lifetime, obviously, but this is development and involves changes programmed by the set of genes the individual acquired at birth in coordination with the individual’s environment. When thinking about the evolution of a characteristic, it is probably best to think about the change of the average value of the characteristic in the population over time. For example, when natural selection leads to bill-size change in medium ground finches in the Galápagos, this does not mean that individual bills on the finches are changing. If one measures the average bill size among all individuals in the population at one time and then measures them in the population several years later, this average value will be different as a result of evolution. Although some individuals may survive from the first time to the second, they will still have the same bill size; however, there will be many new individuals who contribute to the shift in average bill size.

Evolution Explains the Origin of Life

It is a common misunderstanding that evolution includes an explanation of life’s origins. Some of the theory’s critics believe that it cannot explain the origin of life. The theory does not try to explain the origin of life. The theory of evolution explains how populations change over time and how life diversifies the origin of species. It does not shed light on the beginnings of life including the origins of the first cells, which define life. Importantly, biologists believe that the presence of life on Earth precludes the possibility that the events that led to life on Earth can repeat themselves because the intermediate stages would immediately become food for existing living things.

However, once a mechanism of inheritance was in place in the form of a molecule like DNA either within a cell or pre-cell, these entities would be subject to the principle of natural selection. More effective reproducers would increase in frequency at the expense of inefficient reproducers. While evolution does not explain the origin of life, it may have something to say about some of the processes operating once pre-living entities acquired certain properties.

Organisms Evolve on Purpose

Statements such as “organisms evolve in response to a change in an environment” are quite common, but such statements can lead to two types of misunderstandings. First, do not interpret the statement to mean that individual organisms evolve. The statement is shorthand for “a population evolves in response to a changing environment.” However, a second misunderstanding may arise by interpreting the statement to mean that the evolution is somehow intentional. A changed environment results in some individuals in the population, those with particular phenotypes, benefiting and therefore producing proportionately more offspring than other phenotypes. This results in change in the population if the characteristics are genetically determined.

It is also important to understand that the variation that natural selection works on is already in a population and does not arise in response to an environmental change. For example, applying antibiotics to a population of bacteria will, over time, select a population of bacteria that are resistant to antibiotics. The resistance, which a gene causes, did not arise by mutation because of applying the antibiotic. The gene for resistance was already present in the bacteria's gene pool, likely at a low frequency. The antibiotic, which kills the bacterial cells without the resistance gene, strongly selects individuals that are resistant, since these would be the only ones that survived and divided. Experiments have demonstrated that mutations for antibiotic resistance do not arise as a result of antibiotic application.

In a larger sense, evolution is not goal directed. Species do not become “better” over time. They simply track their changing environment with adaptations that maximize their reproduction in a particular environment at a particular time. Evolution has no goal of making faster, bigger, more complex, or even smarter species, despite the commonness of this kind of language in popular discourse. What characteristics evolve in a species are a function of the variation present and the environment, both of which are constantly changing in a nondirectional way. A trait that fits in one environment at one time may well be fatal at some point in the future. This holds equally well for insect and human species.

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• Authors: Mary Ann Clark, Matthew Douglas, Jung Choi
• Publisher/website: OpenStax
• Book title: Biology 2e
• Publication date: Mar 28, 2018
• Location: Houston, Texas
• Book URL: https://openstax.org/books/biology-2e/pages/1-introduction
• Section URL: https://openstax.org/books/biology-2e/pages/18-1-understanding-evolution

© Apr 26, 2024 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License . The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.

• Introduction to Ecology; Major patterns in Earth’s climate
• Behavioral Ecology
• Population Ecology 1
• Population Ecology 2
• Community Ecology 1
• Community Ecology 2
• Ecosystems 1
• Ecosystems 2
• Strong Inference
• What is life?

What is evolution?

• Evolution by Natural Selection
• Other Mechanisms of Evolution
• Population Genetics: the Hardy-Weinberg Principle
• Phylogenetic Trees
• Earth History and History of Life on Earth
• Origin of Life on Earth
• Gene expression: DNA to protein
• Gene regulation
• Cell division: mitosis and meiosis
• Mendelian Genetics
• Chromosome theory of inheritance
• Patterns of inheritance
• Chemical context for biology: origin of life and chemical evolution
• Biological molecules
• Membranes and Transport
• Energy and enzymes
• Respiration, chemiosmosis and oxidative phosphorylation
• Oxidative pathways: electrons from food to electron carriers
• Fermentation, mitochondria and regulation
• Why are plants green, and how did chlorophyll take over the world? (Converting light energy into chemical energy)
• Carbon fixation
• Recombinant DNA
• Cloning and Stem Cells
• Adaptive Immunity
• Human evolution and adaptation

Learning Objectives

• Recall the common features of life on earth
• List the conditions that cause populations of living organisms to evolve
• Distinguish biological evolution of populations from changes to individual organisms over a lifetime.
• Cite evidence that all life on earth has a common origin
• Explain how a scientific “theory” differs from hypothesis or conjecture
• Distinguish between homologous and analogous structures
• Identify common misconceptions about evolution

Life on Earth

Recall from the beginning of this course the five generally agreed upon criteria for life:

• Need for energy
• Organization in membrane-bound cells
• Genetic information
• Ability to replicate
• Change over time

Evolution as an emergent property of life

A key part of any definition of life is that living organisms reproduce. Let’s now add a couple of observations:

• The process of reproduction, while mostly accurate, is imperfect. When cells divide, they have to replicate their DNA. Although DNA replication is highly accurate, it still makes about 1 mistake in 10 million nucleotides. Over generations, the population will contain lots of heritable variation.
• The population of a given type of organism will tend to grow exponentially, but will reach a limit, where the individuals have to compete with each other for the limiting resource (food, space, mates, sunlight, etc.)

Suppose some heritable variations (speed, strength, sharper claws, bigger teeth) make some individuals more competitive for the limiting resource—what will happen? The individuals with superior variants will acquire more resources, and have more progeny. If the superior variants are heritable, then their progeny will have the same superior variants. Over generations, then, a larger and larger proportion of the population will consist of individuals with the superior heritable variants. This is biological evolution.

Biological evolution is defined as change in the heritable characteristics of a population over succeeding generations. In more technical terms, evolution is defined as change in the gene pool of a population, measurable as changes in allele frequencies in a population.

Suppose there is heritable variation in a population, and the heritable variation makes a difference in the survival and reproduction of individual organisms. If these conditions exist, and they do for all natural populations of living organisms, evolution must occur. Life evolves!

Charles Darwin called this process natural selection. He and Alfred Wallace were the first to propose that evolution by natural selection could explain the origin of all the multitudes of species on Earth and how they appear so well-adapted in form and function to their particular environments. Moreover, Darwin proposed that all of life on Earth descended from a common ancestor, via slow, incremental accumulation of heritable (genetic) changes.

Evolution is a theory, not just a hypothesis

Darwin published his theory of evolution in the Origin of Species (1859), with carefully reasoned evidence to support this theory that all life on earth evolved from a common ancestor. This theory has been tested in numerous ways by the work of many thousands of scientists. Every test has produced results that are consistent with the theory. Evolutionary biologists conduct research to elaborate or refine the theory and understand the mechanisms at work in specific populations. Evolutionary theory now forms a framework for biological thinking, so that one famous evolutionary biologist wrote that “ Nothing in Biology Makes Sense Except in the Light of Evolution ” (Dobzhansky, 1973).

The scientific use of the word theory is very different from the casual, every-day use.  A scientific theory is an overarching, unifying explanation of phenomena that is well supported by multiple, independent lines of evidence—i.e., composed of hundreds or thousands of independent, well-supported hypotheses.  For example, germ theory is the theory that explains how microorganisms cause disease, and cell theory explains how cells function as the basic unit of life.

Title page of Darwin’s The Origin of Species, 1859 from Wikipedia

A few key lines of supporting evidence:

• geological and fossil record, showing that the Earth is about 4.5 billion years old, and sequential changes in the kinds and forms of living organisms over geological time scales
• homologies in body plans, structures, and DNA sequences indicative of common ancestry
• a common biochemistry for all life on Earth – the same amino acids, the same biological building blocks, the same genetic code
• inference of evolutionary relationships from gene sequence comparisons largely agree with the fossil record, and are consistent with a common origin for all extant life on Earth.

The video below highlights some of this key supporting evidence in the context of the evolution of whales:

Homologous or Analogous?

In comparing characteristics of organisms, we have to keep in mind that organisms may have similar characteristics either because they inherited the characteristic from a common ancestor, or because they both independently evolved similar characteristics. For example, the tail fins of dolphins, orcas and whales are similar in shape, and they were inherited from a common ancestor of these marine mammals. Their tail fins are homologous,  meaning their similarity is due to inheritance from a common ancestor. On the other hand, the tail fins of orcas and sharks are not homologous, because the common ancestor of all mammals did not have tail fins. They are analogous structures, that evolved independently in sharks and marine mammals. When scientists analyze evolutionary relationships between groups of organisms, they have to be careful to distinguish whether observed similarities between the groups are homologous or analogous.

Common misconceptions about evolution

Here are corrections to some common misconceptions about evolution by natural selection:

• The individual undergoing natural selection does not evolve–it just lives or dies! Instead, the population of organisms evolves. Recall that evolution is the change in allele frequencies, and only populations have allele frequencies. Individuals just have alleles.
• Evolution is not a directed process with a fixed end point, or a best phenotype. Rather, the environment serves as a selective agent . No amount of planning on the part of the organism can predict whether an organism will be a good fit for the environment it finds itself in. An individual cannot “try” to evolve or “anticipate” the types of mutations it should have for future environmental change.
• Organisms, and the genes they contain, do not behave for the ‘good of the species.’ Rather, each individual lives and reproduces, which increases its representation in the gene pool, or it dies or fails to reproduce and is not represented in the gene pool. Those most represented after encountering a selective agent are considered the “most fit” for that environment, in that time and place.
• Selection doesn’t always result in the best possible fit of an organism to its environment because of constraints and trade-offs . Sometimes the same genes that code for a trait also cause a second, suboptimal trait to occur.
• Mutations are not caused or induced as a result of environmental change. Variation is already present in the population. When the environment changes, those individuals that already have some beneficial variation (mutations) that is well suited to the new environment are more likely to survive and reproduce; organisms do not develop new mutations in response to the environmental change.  (And if there is no variation present in the population such that some individuals survive and reproduce, then the population is likely to go extinct).

At its simplest, evolution distills down to the idea that as long as there is variation in a population, as long as that variation is heritable, and as long as there is differential reproductive success (not everyone reproduces equally), then the next generation will be genetically different from the previous generation. We will explore the mechanisms that contribute to evolution over the next class sessions.

For thought and discussion:

Think of some ways that evolution can be or has been tested. What testable predictions arise from evolutionary theory? How does the work of many geologists or some physicists test evolutionary theory? What are some common misconceptions about evolution?

Evolution Resources:

Evolution 101 University of California Berkeley evolution site, a complete resource for learning and teaching about evolution. Engaging, well-illustrated, accurate. How did feathers evolve? Carl Zimmer’s TED-Ed video, 3 1/2 minutes. Evolution animation by Tyler Rhodes, produced from drawings made by children copying a drawing of a salamander-like animal with successive generations of variation, mass extinction and selection. The process is described in this Scientific American blog post  http://blogs.scientificamerican.com/psi-vid/2012/02/29/an-evolution-animation-unlike-any-youve-seen-before/ and Tyler Rhodes blog http://evolutionanimation.wordpress.com/ describes both the drawing “game” and his animation process. His “ wheel of life ” is an amazing phylogenetic tree of the drawings. Newly found: the world’s oldest fossils A post in the Why Evolution Is True blog by Jerry Coyne, explaining the paper by Wacey, D.,M. R. Kilburn, M. Saudners, J. Cliff, and M. D. Wacey et al. 2011.  Microfossils of sulphur-metabolizing cells in 3.4-billion-year-old rocks of Western Australia .  Nature Geoscience online: doi:10.1038/ngeo1238 Darryl Cunningham Investigates: Evolution A lucid, inviting comic-strip presentation of basic evolutionary theory and evidence. Aimed at beginning learners. Nothing in Biology Makes Sense Except in the Light of Evolution Dobzhansky’s 1973 essay in The American Biology Teacher 35:125-129, just as relevant today as then.

UN Sustainable Development Goal (SDG) 14 Life Below Water and SDG 15: Life on Land – Everything evolves! Understanding the common features of life on Earth is crucial for the conservation and protection of Earth’s biodiversity, and potentially for understanding life we may one day find elsewhere!

One Response to What is evolution?

This cell is having quite the existential crisis! Via Beatrice the Biologist pic.twitter.com/C2kRGRzag6 — Carin Anne Bondar (@carinbondar) December 9, 2015

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UC MUSEUM OF PALEONTOLOGY

Understanding Evolution

Your one-stop source for information on evolution

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An introduction to evolution

The definition.

Biological evolution, simply put, is descent with inherited modification. This definition encompasses everything from small-scale evolution (for example, changes in the frequency of different gene versions in a population from one generation to the next) to large-scale evolution (for example, the descent of different species from a shared ancestor over many generations). Evolution helps us to understand the living world around us, as well as its history.

The explanation

Biological evolution is not simply a matter of change over time. Many things change over time: caterpillars turn into moths, trees lose and regrow their leaves, mountain ranges rise and erode, but they aren’t examples of biological evolution because they don’t involve descent with inherited modifications.

All life on Earth shares a common ancestor , just as you and your cousins share a common grandmother. Through the process of descent with modification, this common ancestor gave rise to the diverse species that we see documented in the fossil record and around us today. Evolution means that we’re all distant cousins: humans and oak trees, hummingbirds and whales.

• More Details
• Evo Examples
• Teaching Resources

You can learn lots more about common ancestry in Evo 101: Patterns or in our Tree Room .

Learn about common ancestry in context:

• A fish of a different color
• The legless lizards of LAX
• What has the head of a crocodile and the gills of a fish?

Find  additional lessons, activities, videos, and articles  that focus on common ancestry.

Reviewed and updated June, 2020.

Evolution 101

The history of life: looking at the patterns

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1.3: Scientific Theories

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As you view Know the Difference (Between Hypothesis and Theory) , focus on these concepts: the controversy surrounding the words ‘‘hypothesis’’ and ‘‘theory’’, the scientific use of the words ‘‘hypothesis’’ and ‘‘theory’’, the criteria for a ‘‘hypothesis,’’ the National Academy of Sciences definition of ‘‘theory’’, the meaning of the statement, ‘‘theories are the bedrock of our understanding of nature’’.

The Theory of Evolution

The theory of evolution by natural selection is a scientific theory. Evolution is a change in the characteristics of living things over time. Evolution occurs by a process called natural selection . In natural selection, some living things produce more offspring than others, so they pass more genes to the next generation than others do. Over many generations, this can lead to major changes in the characteristics of living things. The theory of evolution by natural selection explains how living things are changing today and how modern living things have descended from ancient life forms that no longer exist on Earth. No evidence has been identified that proves this theory is incorrect. More on the theory of evolution will be presented in additional concepts.

The Cell Theory

The cell theory is another important scientific theory of biology. According to the cell theory , the cell is the smallest unit of structure and function of all living organisms, all living organisms are made up of at least one cell, and living cells always come from other living cells. Once again, no evidence has been identified that proves this theory is incorrect. More on the cell theory will be presented in additional concepts.

The Germ Theory

The germ theory of disease, also called the pathogenic theory of medicine, is a scientific theory that proposes that microorganisms are the cause of many diseases. Like the other scientific theories, lots of evidence has been identified that supports this theory, and no evidence has been identified that proves the theory is incorrect.

• With repeated testing, some hypotheses may eventually become scientific theories. A scientific theory is a broad explanation for events that is widely accepted as true.
• Evolution is a change species over time. Evolution occurs by natural selection.
• The cell theory states that all living things are made up of cells, and living cells always come from other living cells.
• The germ theory proposes that microorganisms are the cause of many diseases.

Explore More

Use these resources to answer the questions that follow.

Explore More I

• Darwinian Evolution - Science and Theory at Non-Majors Biology: http://www.hippocampus.org/Biology .
• How is the word ‘‘theory’’ used in common language?
• How is the word ‘‘theory’’ used in science?
• Provide a detailed definition for a ‘‘scientific theory’’.

Explore More II

• Concepts and Methods in Biology - Theories and Laws at Non-Majors Biology: http://www.hippocampus.org/Biology .
• What is a scientific law ?
• What is a scientific theory?
• Give two examples of scientific theories.
• Can a scientific theory become a law? Why or why not?
• Contrast how the term theory is used in science and in everyday language.
• Explain how a hypothesis could become a theory.
• Describe the evidence that proves the cell theory is incorrect.

What is Darwin's Theory of Evolution?

Charles Darwin's Theory of Evolution is one of the most solid theories in science. But what exactly is it?

• Natural selection
• Origin of whales
• Rival theories of evolution
• Modern evolutionary synthesis
• Evidence for evolution
• Is evolution controversial?

Additional resources

The Theory of Evolution by natural selection was first formulated in Charles Darwin's book " On the Origin of Species " published in 1859. In his book, Darwin describes how organisms evolve over generations through the inheritance of physical or behavioral traits, as National Geographic explains. The theory starts with the premise that within a population, there is variation in traits, such as beak shape in one of the Galapagos finches Darwin studied. 

According to the theory, individuals with traits that enable them to adapt to their environments will help them survive and have more offspring, which will inherit those traits. Individuals with less adaptive traits will less frequently survive to pass them on. Over time, the traits that enable species to survive and reproduce will become more frequent in the population and the population will change, or evolve, according to BioMed Central . Through natural selection, Darwin suggested, genetically diverse species could arise from a common ancestor . 

Darwin did not know the mechanism by which traits were passed on, according to National Geographic. He did not know about genetics , the mechanism by which genes encode for certain traits and those traits are passed from one generation to the next. He also did not know about genetic mutation, which is the source of natural variation. But future research by geneticists provided the mechanism and additional evidence for evolution by natural selection

What is natural selection?

Darwin chose the term "natural selection" to be in contrast with "artificial selection," in which animal breeders select for particular traits that they deem desirable. In natural selection, it's the natural environment, rather than a human being, that does the selecting.

Put simply, the theory of evolution by means of natural selection can be described as "descent with modification," said Briana Pobiner , an anthropologist and educator at the Smithsonian National Museum of Natural History in Washington, D.C., who specializes in the study of human origins. The theory is sometimes described as "survival of the fittest," but that characterization can be misleading, Pobiner said. Here, "fitness" refers not to an organism's strength or athleticism but rather its ability to survive and reproduce.

Natural selection can alter a species in small ways, causing a population to change color or size over the course of several generations, according to The Natural History Museum . When this process happens over a relatively short period of time and in a species or small group of organisms, scientists call it " microevolution ."

But when given enough time and accumulated changes, natural selection can create entirely new species, a process known as "macroevolution," according to Derek Turner and Joyce C. havstad in " The Philosophy of Macroevolution ." This long-term process is what turned dinosaurs into birds , amphibious mammals (such as an animal called Indohyus ) into whales and a common ancestor of apes and humans into the people, chimps and gorillas we know today. 

Darwin also described a form of natural selection that depends on an organism's success at attracting a mate — a process known as sexual selection, according to Nature Education . The colorful plumage of peacocks and the antlers of male deer are both examples of traits that evolved under this type of selection. 

How did whales evolve?

One of the best examples scientists have of natural selection, is the evolution of whales . By using Darwin's theory as a guide, and understanding how natural selection works, biologists determined that the transition of early whales from land to water occurred in a series of predictable steps.

The evolution of the blowhole, for example, might have started with random genetic changes that resulted in at least one whale having its nostrils farther back on its head, according to Phys.org .

The whales with this adaptation would have been better suited to a marine lifestyle, since they would not have had to completely surface to breathe. Such individuals were more successful and had more offspring. In later generations, more genetic changes occurred, moving the nose farther back on the head.

Other body parts of early whales also changed. Front legs became flippers. Back legs disappeared. Their bodies became more streamlined, and they developed tail flukes to better propel themselves through water, according to the Natural History Museum .

Even though scientists could predict what early whales should look like, for a long time they lacked the fossil evidence to back up their claim. Creationists viewed this absence, not just with regard to whale evolution but more generally, as proof that evolution didn't occur, as pointed out in a Scientific American article .

However, since the early 1990s, scientists have found evidence from paleontology , developmental biology and genetics to support the idea that whales evolved from land mammals. These same lines of evidence support the theory of evolution as a whole.

In the first edition of "On the Origin of Species," Darwin speculated about how natural selection could cause a land mammal to turn into a whale. As a hypothetical example, Darwin used North American black bears ( Ursus americanus ), which were known to catch insects by swimming in the water with their mouths open, according to the Darwin Correspondence Project .

"I can see no difficulty in a race of bears being rendered, by natural selection, more aquatic in their structure and habits, with larger and larger mouths, till a creature was produced as monstrous as a whale," he speculated.

The idea didn't go over very well with the public or with other scientists. Darwin was so embarrassed by the ridicule he received that the swimming-bear passage was removed from later editions of the book. Scientists now know that Darwin had the right idea but the wrong animal. Instead of looking at bears, he should have been looking at cows and hippopotamuses .

Other theories of evolution

Darwin wasn't the first or only scientist to develop a theory of evolution. Around the same time as Darwin, British biologist Alfred Russel Wallace independently came up with the theory of evolution by natural selection, according to the Natural History Museum . However this had little impact.

"The concept of evolution as a historical event was a hot topic among biologists and geologists prior to Darwin’s book because there was so much evidence accumulating, but I suspect biological evolution hadn’t really impinged on people outside of the academic bunker," Dr. P John D. Lambshead, a retired science research leader in marine biodiversity, ecology, and evolution at The Natural History Museum, London, told All About History Magazine . "As long as science knew of no mechanism to explain how evolution happened it could be safely dismissed as a crank idea."

Meanwhile, French biologist Jean-Baptiste Lamarck proposed that an organism could pass on traits to its offspring, though he was wrong about some of the details, according to the University of California’s Museum of Paleontology .

Like Darwin, Lamarck believed that organisms adapted to their environments and passed on those adaptations. He thought organisms did this by changing their behavior and, therefore, their bodies — like an athlete working out and getting buff — and that those changes were passed on to offspring. 

For example, Lamarck thought that giraffes originally had shorter necks but that, as trees around them grew taller, they stretched their necks to reach the tasty leaves and their offspring gradually evolved longer and longer necks. Lamarck also believed that life was somehow driven to evolve through the generations from simple to more complex forms, according to Understanding Evolution , an educational resource from the University of California Museum of Paleontology .

Though Darwin wasn't sure of the mechanism by which traits were passed on, he did not believe that evolution necessarily moved toward greater complexity, according to Understanding Evolution — rather, he believed that complexity arose through natural selection. 

A Darwinian view of giraffe evolution, according to Quanta Magazine , would be that giraffes had natural variation in their neck lengths, and that those with longer necks were better able to survive and reproduce in environments full of tall trees, so that subsequent generations had more and more long-necked giraffes. 

The main difference between the Lamarckian and Darwinian ideas of giraffe evolution is that there's nothing in the Darwinian explanation about giraffes stretching their necks and passing on an acquired characteristic.

What is modern evolutionary synthesis?

According to Pobiner, Darwin did not know anything about genetics. "He observed the pattern of evolution, but he didn't really know about the mechanism," she said. That came later, with the discovery of how genes encode different biological or behavioral traits, and how genes are passed down from parents to offspring. The incorporation of genetics into Darwin's theory is known as "modern evolutionary synthesis."

The physical and behavioral changes that make natural selection possible happen at the level of DNA and genes within the gametes, the sperm or egg cells through which parents pass on genetic material to their offspring. Such changes are called mutations . "Mutations are basically the raw material on which evolution acts," Pobiner said. 

Mutations can be caused by random errors in DNA replication or repair, or by chemical or radiation damage, according to Nature Education . Usually, mutations are either harmful or neutral, but in rare instances, a mutation might prove beneficial to the organism. If so, it will become more prevalent in the next generation and spread throughout the population. 

In this way, natural selection guides the evolutionary process, preserving and adding up the beneficial mutations and rejecting the bad ones. "Mutations are random, but selection for them is not random," Pobiner said.

But natural selection isn't the only mechanism by which organisms evolve, she said. For example, genes can be transferred from one population to another when organisms migrate or immigrate — a process known as gene flow. And the frequency of certain genes can also change at random, which is called genetic drift. 

The reason Lamarck's theory of evolution is generally wrong is that acquired characteristics don't affect the DNA of sperm and eggs. A giraffe's gametes, for example, aren't affected by whether it stretches its neck; they simply reflect the genes the giraffe inherited from its parents. But as Quanta reported , some aspects of evolution are Lamarckian.

For example, a Swedish study published in 2002 in the European Journal of Human Genetics found that the grandchildren of men who starved as children during a famine passed on better cardiovascular health to their grandchildren. Researchers hypothesize that although experiences such as food deprivation don't change the DNA sequences in the gametes, they may result in external modifications to DNA that turn genes "on" or "off."

Such changes, called epigenetic changes, do not modify the actual DNA sequence itself. For instance, a chemical modification called methylation can affect which genes are turned on or off. Such epigenetic changes can be passed down to offspring. In this way, a person's experiences could affect the DNA he or she passes down, analogous to the way Lamarck thought a giraffe craning its neck would affect the neck length of its offspring.

What is the evidence for evolution?

The Theory of Evolution is one of the best-substantiated theories in the history of science. It is supported by evidence from a wide variety of scientific disciplines, including  genetics, which shows that different species have similarities in their DNA . 

There is also evidence supporting the Theory of Evolution in paleontology and geology. This is through the fossil record, which shows how that species that existed in the past are different from those present today, according to Bruce S. Lieberman and Roger L. Kaesler in " Prehistoric Life: Evolution and the Fossil Record " (Wiley, 2010).

There is also evidence for Darwin's theory found in developmental biology . It has been discovered that species that seem very different as adults pass through similar stages of embryological development, suggesting a shared evolutionary past, according to the open-access textbook " Concepts of Biology ." 

Evidence for whale evolution from paleontology

The critical piece of evidence was discovered in 1994, when paleontologists found the fossilized remains of Ambulocetus natans , which means "swimming-walking whale," according to a 2009 review published in the journal Evolution: Education and Outreach . Its forelimbs had fingers and small hooves, but its hind feet were enormous relative to its size. The animal was clearly adapted for swimming, but it was also capable of moving clumsily on land, much like a seal.

When it swam, the ancient creature moved like an otter , pushing back with its hind feet and undulating its spine and tail.

Modern whales propel themselves through the water with powerful beats of their horizontal tail flukes, but A. natans still had a whip-like tail and had to use its legs to provide most of the propulsive force needed to move through water.

In recent years, more and more of these transitional species, or " missing links ," have been discovered, lending further support to Darwin's theory. For example, in 2007, a geologist discovered the fossil of an extinct aquatic mammal, called Indohyus , that was about the size of a cat and had hooves and a long tail. 

Scientists think the animal belonged to a  group related to cetaceans such as Ambulocetus natans . This creature is considered a "missing link" between artiodactyls — a group of hoofed mammals (even-toed ungulates) that includes hippos, pigs, and cows — and whales, according to the National Science Foundation . 

Researchers knew that whales were related to artiodactyls, but until the discovery of this fossil, there were no known artiodactyls that shared physical characteristics with whales. After all, hippos, thought to be cetaceans' closest living relatives , are very different from whales. Indohyus , on the other hand, was an artiodactyl, indicated by the structure of its hooves and ankles, and it also had some similarities to whales, in the structure of its ears, for example.  

Evidence for whale evolution from genetics & developmental biology

Genetic evidence also supports the idea that whales evolved from land mammals and provides information about the exact branching of the evolutionary tree. For instance, in 1999, researchers reported in the journal Proceedings of the National Academy of Sciences that according to genetic analysis of " jumping gene " sequences, which copy and paste themselves into genomes, hippos were whales' closest living relatives. Before 1985, researchers thought pigs were more closely related to whales, but this 1999 study overturned that idea, as the Associated Press reported. 

In 2019, researchers reported in the journal Science Advances about which genes within the whale genome were inactivated during the process of the creature's evolution from land mammals, as Science Friday reported. The researchers could tell that certain genes, including one involved in making saliva, had been inactivated because there are remnants of them, which the researchers call genomic fossils, in whale genomes. This indicates that whales evolved from a salivating creature.  

There's also evidence of cetacean evolution from developmental biology. Developmental biology illustrates the fact that animals that are very different as adults share similarities as embryos because they are evolutionarily related. For example, as embryos, cetaceans started to develop hind limbs, which disappear later in development, while the forelimbs remain and develop into flippers, according to the journal Evolution: Education and Outreach . This suggests that cetaceans evolved from a four-legged ancestor.

Is the theory of evolution controversial?

Despite the wealth of evidence from the fossil record, genetics and other fields of science, some people still question the theory of evolution 's validity. Some politicians and religious leaders denounce the theory, invoking a higher being as a designer to explain the complex world of living things, especially humans.

School boards debate whether the theory of evolution should be taught alongside other ideas, such as intelligent design or creationism. 

Mainstream scientists see no controversy. "A lot of people have deep religious beliefs and also accept evolution," Pobiner said, adding, "there can be real reconciliation."

Evolution is well supported by many examples of changes in various species leading to the diversity of life seen today. "Natural selection, or to put it another way — variation, heredity, and differential fitness — is the core theory of modern biology," John Lambshead explains. "It is to biology what, say quantum mechanics and special relativity are to physics or the atomic model is to chemistry."

Additional reporting by contributors Alina Bradford, Ashley P. Taylor and Callum McKelvie

• The National Oceanic and Atmospheric Administration has a presentation on whale evolution.
• To read the theory in its original form, see Darwin's book, " On the Origin of Species ."
• Check out this article for an overview of natural selection.
• To understand the difference between a theory and fact, see this National Academy of Sciences website .

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Tom Garner is the Features Editor for History of War magazine and also writes for sister publication All About History . He has a Master's degree in Medieval Studies from King's College London and has also worked in the British heritage industry for the Shakespeare Birthplace Trust , as well as for English Heritage and the National Trust . He specializes in Medieval History and interviewing veterans and survivors of conflicts from the Second World War onwards. 

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Evolution: Fact and Theory

A student measures a hominid skull.

Scientific understanding requires both facts and theories that can explain those facts in a coherent manner. Evolution, in this context, is both a fact and a theory. It is an incontrovertible fact that organisms have changed, or evolved, during the history of life on Earth. And biologists have identified and investigated mechanisms that can explain the major patterns of change.

Patterns in Nature

The field of evolutionary biology seeks to provide explanations for four conspicuous patterns that are manifest in nature. The first three concern living species, whereas the fourth relates to fossils.

• Genetic variation. There is tremendous genetic diversity within almost all species, including humans. No two individuals have the same DNA sequence, with the exception of identical twins or clones. This genetic variation contributes to phenotypic variation – that is, diversity in the outward appearance and behavior of individuals of the same species.
• Adaptation. Living organisms have morphological, biochemical, and behavioral features that make them well adapted for life in the environments in which they are usually found. For example, consider the hollow bones and feathers of birds that enable them to fly, or the cryptic coloration that allows many organisms to hide from their predators. These features may give the superficial appearance that organisms were designed by a creator (or engineer) to live in a particular environment. Evolutionary biology has demonstrated that adaptations arise through selection acting on genetic variation.
• Divergence. All living species differ from one another. In some cases, these differences are subtle, while in other cases the differences are dramatic. Carl Linnaeus (1707-1778) proposed a classification that is still used today with slight changes. In the modern scheme, similar species are grouped into genera, similar genera into families, and so on. This hierarchical pattern of relationship produces a tree-like pattern, which implies a process of splitting and divergence from a common ancestor.
• Fossil species. Fossils are the mineralized remnants or impressions of once-living organisms. Many fossils, such as trilobites and dinosaurs, belong to groups that no longer exist on the face of the Earth. Conversely, many modern species appear similar to other fossils, yet fossils of the modern species are absent from rocks of corresponding ages. The age of the Earth is estimated to be about 4.5 billion years, with the earliest bacterial fossils about 3.5 billion years old. Fossils from around 550 million years ago (the Cambrian period) show a diverse assemblage of multicellular animals.

Evolutionary biology provides a scientific framework for understanding the changes that have occurred since the first life forms arose on Earth several billion years ago. Biochemists, geologists, and physicists seek natural explanations for the origin of life on Earth. While progress has been made in this area, the origin of life remains an interesting, but unanswered, question.

Mechanisms of Evolution

• Biological evolution results from changes over time in the genetic constitution of species. Genetic changes often, but not always, produce noticeable changes in the appearance or behavior of organisms. Evolution requires both the production of variation and the spread of some variants that replace others.
• Genetic variation arises through two processes, mutation and recombination. Mutation occurs when DNA is imperfectly copied during replication, leading to a difference between a parent’s gene and that of its offspring. Some mutations affect only one bit in the DNA; others produce rearrangements of large blocks of DNA.
• Recombination occurs when genes from two parents are shuffled to produce an offspring, as happens regularly in sexual reproduction. Usually the two parents belong to the same species, but sometimes (especially in bacteria) genes move between more distantly related organisms.
• The fate of any particular genetic variant depends on two processes, drift and selection. Drift refers to random fluctuations in gene frequency, and its effects are usually seen at the level of DNA. Ten flips of a coin do not always produce exactly five heads and five tails; drift refers to the same statistical issue applied to the transmission of genetic variants across generations.
• The principle of natural selection was discovered by Charles Darwin (1809-1882), and it is the process by which organisms become adapted to their environments. Selection occurs when some individual organisms have genes that encode physical or behavioral features that allow them to better harvest resources, avoid predators, and such relative to other individuals that do not carry the same genes. The individuals that have these useful features will tend to leave more offspring than other individuals, so the responsible genes will become more common over time, leading the population as a whole to become better adapted.
• The process that many people find most confusing about evolution is speciation, which is not a separate mechanism at all, but rather a consequence of the preceding mechanisms played out in time and space. Speciation occurs when a population changes sufficiently over time that it becomes convenient to refer to the early and late forms by different names. Speciation also occurs when one population splits into two distinct forms that can no longer interbreed. Reproductive isolation does not generally happen in one generation; it may require many thousands of generations when, for example, one part of a population becomes geographically separated from the rest and adapts to a new environment. Given time, it is inevitable that two populations that live apart will diverge by mutation, drift, and selection until eventually their genes are no longer compatible for successful reproduction.

Evidence for Evolution, and its Significance in our Lives:

It is impossible to review all the evidence for evolution in a short article such as this. However, the following offers a sample of the kinds of evidence that have been discovered and confirmed repeatedly by scientists. These examples also illustrate the importance of this evidence for science and society more generally.

• Evidence from fossils . Based on myriad similarities and differences between living species, evolutionary biology makes predictions about the features of ancestral forms. For example, numerous features indicate that birds are derived from reptilian ancestors. By contrast, these data reject the possibility that birds were derived from other groups, such as flying insects. Scientists have discovered fossil birds with feathers and legs like modern birds, but which also have teeth, clawed digits on their forelimbs, and a tailbone like their reptilian ancestors. Fossils are especially important evidence for evolution because, with little effort, each of us can use our eyes and minds to observe and interpret the dinosaur and other ancient fossils in public museums.
• Evidence from genetics. The genomes of all organisms contain overwhelming evidence for evolution. All living species share the same basic mechanism of heredity using DNA (or RNA in some viruses) to encode genes that are passed from parent to offspring, and which are transcribed and translated into proteins during each organism’s life. Using DNA sequences, biologists quantify the genetic similarities and differences among species, in order to determine which species are more closely related to one another and which are more distantly related. In doing so, biologists use essentially the same evidence and logic used to determine paternity in lawsuits. The pattern of genetic relatedness between all species indicates a branching tree that implies divergence from a common ancestor. Within this tree of life, there are also occasional reticulations where two branches fuse, rather than separate. (For example, mitochondria are organelles found in the cells of plants and animals. Mitochondria have their own genes, which are more similar to genes in bacteria than to genes on the chromosomes in the cell nucleus. Thus, one of our distant ancestors arose from a symbiosis of two different cell types.) The genetic similarity between species, which exists by virtue of evolution from the same ancestral form, is an essential fact that underlies biomedical research. This similarity allows us to begin to understand the effects of our own genes by conducting research on genes from other species. For example, genes that control the process of DNA repair in bacteria, flies, and mice have been discovered to influence certain cancers in humans. These findings also suggest strategies for intervention that can be explored in other species before testing on humans.
• Evolution in action. Evolutionary change continues to this day, and it will proceed so long as life itself exists. In recent years, many bacterial pathogens have evolved resistance to antibiotics used to cure infections, thereby requiring the development of new and more costly treatments. In some frightening cases, bacteria have evolved resistance to every available antibiotic, so there is no longer any effective treatment. In the case of HIV, which causes AIDS, significant viral evolution occurs within the course of infection of a single patient, and this rapid evolution enables the virus to evade the immune system. Many agricultural pests have evolved resistance to chemicals that farmers have used for only a few decades. As we work to control diseases and pests, the responsible organisms have been evolving to escape our controls. Moreover, scientists can perform experiments to study evolution in real time, just as experiments are used to observe dynamic processes in physics, chemistry, and other branches of biology. To study evolution in action, scientists use organisms like bacteria and fruit flies that reproduce quickly, so they can see changes that require many generations.

Conclusions

Evolutionary biology is a strong and vigorous field of science. A theoretical framework that encompasses several basic mechanisms is consistent with the patterns seen in nature; and there is abundant evidence demonstrating the action of these mechanisms as well as their contributions to nature. Hence, evolution is both a theory and a set of established facts that the theory explains.

Like every other science, there is scientific debate about some aspects of evolution, but none of these debates appear likely to shake the foundations of this field. There exists no other scientific explanation that can account for all the patterns in nature, only non-scientific explanations that require a miraculous force, like a creator. Such super-natural explanations lie outside of science, which can neither prove nor disprove miracles. Science provides us with a compelling account and explanation of the changing life on Earth. It should also remind us of our good fortune to have come into being and our great responsibility to ensure the continuity of life.

Originally published on ActionBioscience and republished by permission of the American Institute of Biological Sciences.

© 2000, American Institute of Biological Sciences. Educators have permission to reprint articles for classroom use.

Richard E. Lenski is an American evolutionary biologist, a MacArthur fellow, a Hannah Distinguished Professor of Microbial Ecology at Michigan State University, and a member of the National Academy of Sciences.

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• Teaching Evolution through Human Examples

The "Teaching Evolution through Human Examples"  (TEtHE) three-year exploratory research and development project was funded by National Science Foundation Discovery Research K-12 grant #1119468. The project has created four curriculum units for Advanced Placement (AP) Biology classes, aligned to the learning objectives, using human case studies to teach core evolutionary principles. The curriculum units are: (1) Adaptation to Altitude, (2) Malaria, (3) Evolution of Human Skin Color, and (4) What Does It Mean To Be Human?. The project has also created a CRS (Cultural and Religious Sensitivity) Teaching Strategies Resource to help teachers create a comfortable and supportive classroom environment for teaching evolution. More information about the project can be found here. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

All of our resources are downloadable here for free! 

Click on this link:   bit.ly/TeachHumanEvolution

You can also read two research articles in the journal Evolution: Education and Outreach, one published in April 2018 and one published in January 2019 , about the effectiveness of these materials. 

CURRICULUM UNITS

The curriculum units contain 4-5 lessons and are designed to be taught over 5-9 days (depending on the unit, whether or not the FULL or CONDENSED lessons are used,  and whether or not optional steps are included. Each version has an accompanying powerpoint file for teaching purposes and a student workbook where all student handouts are collated.

Adaptation to Altitude: Students learn how to devise an experiment to test the difference between acclimation and adaptation; investigate how scientific arguments show support for natural selection in Tibetans; design an investigation using a simulation based on the Hardy-Weinberg principle to explore mechanisms of evolution; and devise a test for whether other groups of people have adapted to living at high altitudes.

Evolution of Human Skin Color: Students examine evidence for the relationship between UV and melanin in other animals; investigate the genetic basis for constitutive skin color humans; learn to test for natural selection in mouse fur color; investigate how interactions between UV and skin color in humans can affect fitness; design an investigation using a simulation based on the Hardy-Weinberg principle to explore mechanisms of evolution; and explore data on migrations and gene frequency to show convergent evolution of skin color.

Malaria: Students examine evidence to compare four different explanations for why many malarial parasites are resistant to antimalarial drugs; investigate how scientific arguments using G6PD data show support for natural selection in humans; design an investigation using a simulation based on the Hardy-Weinberg principle to explore mechanisms of evolution; and apply their understanding to other alleles that have evolved in response to malaria.

What Does It Mean to be Human?: Using a strong nature of science component, students use different types of data to infer / interpret phylogenies among domains, within the vertebrates, and within primates while reflecting on how they answer the question “What do you think it means to be human?” and choose a characteristic that changed substantially in the human family tree to develop a scientific argument based on evidence for when the character evolved.

CRS (CULTURAL AND RELIGIOUS SENSITIVITY) TEACHING STRATEGIES RESOURCE

Description:

The Cultural and Religious Sensitivity (CRS) Teaching Strategies Resource is intended to help create a nonthreatening classroom environment where an opportunity for understanding the scientific account of evolution is possible, and to both encourage and help equip high school teachers to promote positive dialogue around the topic of evolution in their classrooms. The CRS resource complements the TEtHE curriculum units created for AP high school biology courses. However, the CRS resource should also prove valuable for use with general introductory biology students.

Part 1 provides concise foundational information on topics including insight into the nature of science as pertinent to managing a conflict between science and religion; the range of creationists views; the variety of possible relationships between science and religion including examples of how individuals accommodate evolution and religion; and the historical context and background on legal cases dealing with the teaching of evolution. For teachers seeking a proactive approach that acknowledges the cultural and religious controversies and encourages a classroom exploration of the impact of these controversies on the understanding of evolution, Part 2 provides activities to engage students in two 50-75 minute directed classroom discussions. Each classroom activity has an accompanying powerpoint file for teaching purposes.

Classroom Activity 1 , Directed Discussions: “Why Study Evolution” , is designed to be used at the start of instruction on evolutionary theory in classrooms where teachers are aware that many of their students have been exposed to only negative and/or mistaken notions of evolutionary theory and to provide an opportunity for students’ concerns to be acknowledged.

Activity 1 feedback:

(teacher) "This was the first time I have taken class time to address the question 'Why study evolution?". In years past, I took for granted that everyone would be on board, and if they were not there was not much I could do about it. I appreciate the way this structured lesson helped me slow down and acknowledge that certain people have doubts about the evidence for evolution. Those doubts should not have to be muffled. There is space for such dialogue, without diminishing the significance of evolution to the study of biology".

(student) "It just kind of brought you to think about what your views on evolution are because I'm pretty devoutly religious. It was interesting to think about like, how my beliefs can mesh with evolution and I could still believe in science."

(student) "I really like how the lessons ease you into evolution, the idea of it, because most people are not open to learning it, so it's kind of helping you not to have to be bombarded..."

Classroom Activity 2 ,  A Historical Role Play: “How Do People Think about Evolutionary Theory” , is designed to be used at the end of the instruction on evolution, and to reinforce that instruction, in classrooms where teachers believe that anti-evolutionism is a non-existent or minority viewpoint.

Activity 2 feedback:

(student) "I was a little concerned at first because I knew a little bit of background about this debate and I knew it would have a lot of religion in it and I'm religious myself so I was a little worried about people bashing my views, but it didn't really get to that so I was happy."

(student) "It was interesting to have to defend a point of view that you might not agree with in your everyday opinions. It just makes you think about the different views and like how you could like see how that could work but from the modern standpoint that we had to do, how it could be wrong." 

(student) "I considered it a little bit of a capstone because we learned about evolution and then we had to put in what our current response would be to theirs so we had to formulate our own kind of argument based on what we have already learned..."

RESEARCH AND IMPLEMENTATION SUMMARY

The curriculum units were reviewed by teachers, other educators, and scientists, field tested (round 1) by 5 teachers, revised, and then field tested (round 2) by 15 teachers and 470 students in 10 states across the US. Our preliminary results indicate that the curriculum units increased understanding of, attitude towards, and interest in evolution. Most of the students surveyed indicated that they enjoyed learning about evolution through human examples as much or more than using other examples. The CRS resource was field tested by a subset of 8 of the curriculum unit field test teachers and 160 students, and we found a greater effect on students understanding of evolution for those students who experienced one of the in-class CRS activities.

We are very grateful to our field test teachers and their students! Thanks to: Sydney Bergman, Lisa Boyer, Christy Clark, Donna Considine, Melissa Csikari, Frank Fitzgibbon, Matthew Foret, Lauren Fuller, Cindy Gay, David Knuffke, Alison Loeper, Melinda Malcore, Susan Park, Eileen Pascucci, Tamara Pennington, Phyllis Robinson, Jennifer Shake, and Suzanne Sikes.

We are also grateful to our expert educators: Nikki Chambers (West High School, CA); Chelsea Crawford (Fremont Union High School District, CA);  Mark Terry (The Northwest School, WA); Brad Williamson (UKanTeach Program, KS), and David Pinkerton (independent educational consultant) - and scientists: Cynthia Beall (Case Western University); Holly Dunsworth (University of Rhode Island); Carla Easter (NGHRI); Nina Jablonski (Pennsylvania State University); and Mark Schwartz (NYU School of Medicine) for reviewing multiple versions of our curriculum units.

We are also grateful to Jennifer Clark (Illustrator), Norma Oldfield (illustration research assistant), Anna Ragni (Illustration research assistant), and Matthew Ferry (data collection and entry assistant).

PROJECT PERSONNEL

Project PI is Briana Pobiner (Smithsonian Institution), and project co-PIs are Rick Potts (Smithsonian Institution) and Bill Watson (Diocese of Camden Office of Catholic Schools).

Senior Personnel are Paul Beardsley (Cal Poly Pomona - author of curriculum units); Connie Bertka (Science and Society Resources - author of CRS Resource); and Jay Labov (National Academy of Sciences) and the National Academy of Sciences Teacher Advisory Council; Christopher Lazzaro (College Board); and Kathryn Race (Race and Associates - project evaluator).

Advisory Board members are: Jennifer Bricken (Howard Hughes Medical Institute); Juliet Crowell (Smithsonian Institution); Dennis Liu (Howard Hughes Medical Institute); David Long (George Mason University); Sharon Lynch (George Washington University); Lee Meadows (University of Alabama at Birmingham); and Anna Thanukos (UCMP Berkeley).

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All Human Existence May Have Begun in a Black Hole, Some Scientists Believe

There’s an intriguing possibility that the emergence of conscious life is not just a coincidence, but an inevitable outcome of cosmic evolution.

So let’s contemplate something simpler: why does the universe allow us to exist? Yet again, we run into the same problem: if the universe didn’t allow us to exist, we wouldn’t be here to think about it. This is called the “anthropic principle.” For some, it’s the only answer we need to explain, well , everything; but for others, it’s a philosophical thorn in the side. Everything we know about the universe so far—dating back to the 16th-century Polish astronomer Copernicus, who first proposed that Earth travels around the sun rather than the other way around—tells us that we have no special place in the cosmos. We are not at the center. This is the “Copernican principle.”

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The anthropic and Copernican principles are conflicting axioms about the universe’s existence and our place within it. The anthropic principle says the universe depends on our being here. Meanwhile, the Copernican principle says that we are not special, and no law of physics should depend on our existence. Yet, the vast and ancient universe we see in our telescopes appears to balance both principles, like a pin balanced on the edge of a glass.

So why is our universe the way it is, and why do we exist as self-aware beings , tiny in size and minuscule in lifespan, relative to the lonely cosmic vastness mostly devoid of life? If the universe were made just for us, surely it would be small, human sized, perhaps just one planet or solar system or galaxy, not billions. Why should a universe made for us have black holes, for example? They seem to contribute nothing to our welfare.

Some scientists believe the universe wasn’t finely tuned to create intelligent life like us at all. Instead, they say, the universe evolved its own insurance policy by creating as many black holes as possible, which is the universe’s method of reproduction. Following this line of thinking, the universe itself may very well be alive—and the fact that we humans exist at all is just a happy side effect.

A Finely-Tuned Universe

One of the biggest philosophical problems with the universe is that it has to be finely tuned for us to even exist. If the universe were random, things would quickly become messy. If modified only a tiny bit one way or another, physical parameters such as the speed of light ; the mass of the electron, proton, and neutron ; the gravitational constant ; and so on would eliminate all life—possibly all matter itself—and even the universe as a whole would not last long enough to evolve anything. For example, if their masses were slightly different, protons would decay into neutrons instead of the other way around, and as a result, there would be no atoms.

One possible solution to fine tuning is the multiverse . In this speculative theory, our universe is one of many in the same way that the planet Earth is one of many planets. Different universes have different laws of physics and, therefore, that ours supports life is simply a matter of luck. While some theories of the multiverse propose that these universes are essentially random and have no relationship to one another, one particular multiverse theory suggests that universes in fact reproduce like living beings and have ancestors and descendants. This theory is called cosmological natural selection (or CNS for short). First proposed by theoretical physicist Lee Smolin in 1992, the CNS theory is a strong contender for why our universe seems to balance both the Anthropic and Copernican principles.

When we look at the complexity of living things and the sheer number of non-living configurations there are, we’re left to assume that there’s no way species could appear randomly. Hence, some powerful being must have created all types of living creatures individually as a watchmaker builds a watch, the thinking often goes. However, Charles Darwin’s theory of evolution, which he first posited in his 1859 book, On the Origin of Species, provides a mechanism that explains why living things are non-random. Their parameters are not freely chosen; they are the product of natural selection , the process by which members of a species that are better fit to survive and/or reproduce more effectively are more likely to pass on their genes.

The theory of evolution is one of the greatest success stories in the history of science because it provided a mechanism by which a thing that is highly ordered, complex, and finely tuned for its survival could arise from natural processes. The theory was successful not only because it explained how species arise, but also because it generated new predictions that we could then test. For example, the theory of evolution explains why species appear related to one another.

The Beauty in Black Holes

The cosmological natural selection theory solves the pernicious problem of a universe finely tuned for life. That idea may make sense to us, living on a planet full of complex, multicellular organisms, but Earth is surrounded by mostly dead space and, as far as we know, dead planets, and moons and light years of interstellar dust and stray photons.

Earth is finely tuned for life; the universe is not. However, the cosmological natural selection theory says that the universe is finely tuned for something else: its method of reproduction, giving birth to new universes.

Under the CNS theory framework, every black hole becomes a baby universe . Our universe, likewise, started out as a black hole in its mother universe. The theory says that inside every black hole, the central singularity—which is matter highly compressed in space in the mother universe—becomes a highly compressed point in time in the new universe. This point expands, creating new matter and energy. You get a complete universe from even a tiny black hole .

This means that our universe is finely tuned not for life, but for black holes, which typically come from massive stars (although they can have other origins). It turns out that massive star formation depends on an element also important for life on Earth: carbon.

Carbon monoxide is the second-most common molecule in the universe after molecular hydrogen, even more common than water. In the molecular clouds of gas and dust that form from supernovae, massive stars coalesce amid gaseous carbon monoxide molecules, which act as a coolant. This cooling helps matter clump together and form the stars. Carbon is a critical component in all life that we know of. Therefore, life is, in fact, a byproduct of stellar formation, which is itself a byproduct of what the universe evolved to do: create as many black holes as possible.

The cosmological natural selection theory helps explain why our universe is so highly ordered, complex, and self-sustaining like Darwin’s theory explains the same for living things. That leads to the tantalizing, if speculative, conclusion that perhaps, by some definition, our universe itself is alive.

Dr. Tim Andersen is a principal research scientist at Georgia Tech Research Institute. He earned his doctorate in mathematics from Rensselaer Polytechnic Institute in Troy, New York, and his undergraduate degree from the University of Texas at Austin. He has published academic works in statistical mechanics, fluid dynamics (including a monograph on vortex filaments), quantum field theory, and general relativity. He is the author of The Infinite Universe on Medium and Stubstack and a book by the same name. He lives with his wife and two cats, and has a son and daughter at home as well as one grown son.

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Scientists Found a Paradox in Evolution—and It May Become the Next Rule of Biology

It may have fewer than many of the other sciences, but biology does have two dozen or so “rules”—broad generalizations about the behavior or nature and evolution.

Now, USC researchers want to add a new rule called “selectively advantageous instability (SAI),” which explores how instability can actually benefit a cell and a cellular organism.

The flipside of this “rule” is that SAI can also be a key factor to things like disease and aging, so understanding this process could aid in exploration of those biological processes.

Across the sciences, rules and laws help us make sense of the world around us, whether applied to cosmic scales or subatomic ones. However, in the biological world, things are a bit more complicated. That’s because nature is often full of biological exceptions, and so “rules of biology ” are also considered broad generalizations rather than absolute facts that explain and govern all known life.

Some of these broad generalizations include things like Allen’s Law, which dictates that body shapes in endotherms (warm-blooded animals) adapt to climatic conditions—short and stocky helps retain heat in cold climates, while tall and lanky helps dissipate heat in warmer ones. Another “law,” known as Bergmann’s rule, states that species of a broadly distributed clade tend to be larger in colder climates and smaller in warmer ones (though of course, as with most biological rules, exceptions apply ).

Some two dozen or so rules currently exist that describe all kinds of processes of the natural world, and now, researchers as the University of Southern California (USC) hope to add a new rule. At first glance, this new rule—called “selectively advantageous instability,” or SAI—seems to defy the underpinning assumptions of life in general, and pushes against the current assumption that life craves stability and a conservation of resources.

While nature does tend toward stability (it’s one reason why we see so many hexagonal shapes in the wild, including honeycombs and insect eyes), USC molecular biologist John Towers argues that instability in biological components like proteins and genes can actually be helpful to cells. The study was published last week in the journal Frontiers in Aging .

“Even the simplest cells contain proteases and nucleases and regularly degrade and replace their proteins and RNAs, indicating that SAI is essential for life,” Tower said in a press statement . “This can favor the maintenance of both a normal gene and a gene mutation in the same cell population, if the normal gene is favorable in one cell state and the gene mutation is favorable in the other cell state.”

These states allow for greater genetic diversity, which in turn can make organisms more adaptable. Many cell components also favor a short lifespan, as this actually helps promote cell health. This indicates that SAI in these components is a necessary biological function.

Of course, there are plenty of downsides to instability. This energy-requiring process of mutation instability can introduce deleterious cells that contribute to aging , while also inducing other types of damage and dysfunction.

“Aging has proven to be difficult to define, but most definitions include an increased chance of death with age, and decreased reproductive fitness with age,” the paper reads. “SAI can create a cost for the replicator in terms of energy and/or materials, and this cost might be interpreted in terms of promoting aging.”

Another piece of evidence supporting SAI’s ubiquity and its candidacy as a new “rule of biology” is that it crops up in other well-known concepts, including chaos theory and ideas of “cellular consciousness.” Because of this—as well as its links to fundamental biological processes like aging—understanding the inner workings of SAI could help biologists explore cellular life in a whole new way.

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AP®︎/College Biology

Course: ap®︎/college biology   >   unit 7.

• Earth formation
• Beginnings of life
• Origins of life

Hypotheses about the origins of life

• The RNA origin of life
• Origins of life on Earth

Key points:

• The Earth formed roughly 4.5 ‍   billion years ago, and life probably began between 3.5 ‍   and 3.9 ‍   billion years ago.
• The Oparin-Haldane hypothesis suggests that life arose gradually from inorganic molecules, with “building blocks” like amino acids forming first and then combining to make complex polymers.
• The Miller-Urey experiment provided the first evidence that organic molecules needed for life could be formed from inorganic components.
• Some scientists support the RNA world hypothesis , which suggests that the first life was self-replicating RNA. Others favor the metabolism-first hypothesis , placing metabolic networks before DNA or RNA.
• Simple organic compounds might have come to early Earth on meteorites.

Introduction

When did life appear on earth, the earliest fossil evidence of life, how might life have arisen.

• Simple inorganic molecules could have reacted (with energy from lightning or the sun) to form building blocks like amino acids and nucleotides, which could have accumulated in the oceans, making a "primordial soup." 3 ‍  
• The building blocks could have combined in further reactions, forming larger, more complex molecules (polymers) like proteins and nucleic acids, perhaps in pools at the water's edge.
• The polymers could have assembled into units or structures that were capable of sustaining and replicating themselves. Oparin thought these might have been “colonies” of proteins clustered together to carry out metabolism, while Haldane suggested that macromolecules became enclosed in membranes to make cell-like structures 4 , 5 ‍   .

From inorganic compounds to building blocks

Were miller and urey's results meaningful, from building blocks to polymers, what was the nature of the earliest life, the "genes-first" hypothesis, the "metabolism-first" hypothesis, what might early cells have looked like, another possibility: organic molecules from outer space.

• Miller, Urey, and others showed that simple inorganic molecules could combine to form the organic building blocks required for life as we know it.
• Once formed, these building blocks could have come together to form polymers such as proteins or RNA.
• Many scientists favor the RNA world hypothesis, in which RNA, not DNA, was the first genetic molecule of life on Earth. Other ideas include the pre-RNA world hypothesis and the metabolism-first hypothesis.
• Organic compounds could have been delivered to early Earth by meteorites and other celestial objects.

Works cited:

• Harwood, R. (2012). Patterns in palaeontology: The first 3 billion years of evolution. Palaeontology , 2(11), 1-22. Retrieved from http://www.palaeontologyonline.com/articles/2012/patterns-in-palaeontology-the-first-3-billion-years-of-evolution/ .
• Wacey, D., Kilburn, M. R., Saunders, M., Cliff, J., and Brasier, M. D. (2011). Microfossils of sulphur-metabolizing cells in 3.4-billion-year-old rocks of Western Australia. Nature Geoscience , 4 , 698-702. http://dx.doi.org/10.1038/ngeo1238 .
• Primordial soup. (2016, January 20). Retrieved May 22, 2016 from Wikipedia: https://en.wikipedia.org/wiki/Primordial_soup .
• Gordon-Smith, C. (2003). The Oparin-Haldane hypothesis. In Origin of life: Twentieth century landmarks . Retrieved from http://www.simsoup.info/Origin_Landmarks_Oparin_Haldane.html .
• The Oparin-Haldane hypothesis. (2015, June 14). In Structural biochemistry . Retrieved May 22, 2016 from Wikibooks: https://en.wikibooks.org/wiki/Structural_Biochemistry/The_Oparin-Haldane_Hypothesis .
• Kimball, J. W. (2015, May 17). Miller's experiment. In Kimball's biology pages . Retrieved from http://www.biology-pages.info/A/AbioticSynthesis.html#Miller's_Experiment .
• Earth’s early atmosphere. (Dec 2, 2011). In Astrobiology Magazine . Retrieved from http://www.astrobio.net/topic/solar-system/earth/geology/earths-early-atmosphere/ .
• McCollom, T. M. (2013). Miller-Urey and beyond: What have learned about prebiotic organic synthesis reactions in the past 60 years? Annual Review of Earth and Planetary Sciences , 41_, 207-229. http://dx.doi.org/10.1146/annurev-earth-040610-133457 .
• Powner, M. W., Gerland, B., and Sutherland, J. D. (2009). Synthesis of activated pyrimidine ribonucleotides in prebiotically plausible conditions. Nature , 459 , 239-242. http://dx.doi.org/10.1038/nature08013 .
• Lurquin, P. F. (June 5, 2003). Proteins and metabolism first: The iron-sulfur world. In The origins of life and the universe (pp. 110-111). New York, NY: Columbia University Press.
• Ferris, J. P. (2006). Montmorillonite-catalysed formation of RNA oligomers: The possible role of catalysis in the origins of life. Philos. Trans. R. Soc. Lond. B. Bio.l Sci ., 361 (1474), 1777–1786. http://dx.doi.org/10.1098/rstb.2006.1903 .
• Kimball, J. W. (2015, May 17). Assembling polymers. In Kimball's biology pages . Retrieved from
• Montmorillonite. (2016, 28 March). Retrieved May 22, 2016 from Wikipedia: https://en.wikipedia.org/wiki/Montmorillonite .
• Wilkin, D. and Akre, B. (2016, March 23). First organic molecules - Advanced. In CK-12 biology advanced concepts . Retrieved from http://www.ck12.org/book/CK-12-Biology-Advanced-Concepts/section/10.8/ .
• Hollenstein, M. (2015). DNA catalysis: The chemical repertoire of DNAzymes. Molecules , 20 (11), 20777–20804. http://dx.doi.org/10.3390/molecules201119730 .
• Breaker, R. R. and Joyce, G. F. (2014). The expanding view of RNA and DNA function. Chemistry & biology , 21 (9), 1059–1065. http://dx.doi.org/10.1016/j.chembiol.2014.07.008 .
• Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., and Walter, P. (2002). A pre-RNA world probably predates the RNA world. In Molecular biology of the cell (4th ed.). New York, NY: Garland Science. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK26876/#_A1124_ .
• Moran, L. A. (2009, May 15). Metabolism first and the origin of life. In Sandwalk: Strolling with a skeptical biochemist . Retrieved from http://www.simsoup.info/Origin_Landmarks_Oparin_Haldane.html .
• Kimball, J. W. (2015, May 17). The first cell? In Kimball's biology pages . Retrieved from http://www.biology-pages.info/A/AbioticSynthesis.html#TheFirstCell?
• Kimball, J. W. (2015, May 17). Molecules from outer space? In Kimball's biology pages . Retrieved from http://www.biology-pages.info/A/AbioticSynthesis.html#Molecules_from_outer_space? .
• Jeffs, W. (2006, November 30). NASA scientists find primordial organic matter in meteorite. In NASA news . Retrieved from http://www.nasa.gov/centers/johnson/news/releases/2006/J06-103.html .

Additional references:

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How sweat and stamina helped make humans exceptional runners–and hunters

By Laura Baisas

Posted on May 13, 2024 11:00 AM EDT

3 minute read

Rock art from Tadrart Acacus in Libya. This rocky massif is home to thousands of cave paintings in very different styles, dating from 12,000 BCE to 100 CE. They reflect marked changes in the fauna and flora, and also the different ways of life of the populations that succeeded one another in this region of the Sahara. © Federica Leone/UNESCO

Endurance running is not just a hobby for modern marathoners or for posting on social media. A new look into the anthropological history of endurance running when hunting for game shows that it may be just as efficient as other more traditional hunting methods like foraging . The findings are described in a study published May 13 in the journal Nature Human Behaviour and supports an idea called the endurance pursuit hypothesis .

“People who frequently practice running will know that when practiced on a regular basis, running becomes relatively easy,” study co-authors and evolutionary anthropologists Eugène Morin of Trent University in Canada and Bruce Winterhalder from the University of California, Davis tell PopSci . “From this, it is easy to envision how it could have conferred a selective advantage in hunting.”

What is the endurance pursuit hypothesis?

Initially, some anthropologists believed that running long distances in pursuit of game would have been taxing to the human body and not worth the trouble. A more slow paced pursuit was believed to be the better method to both get food while preserving strength . 

Endurance pursuit hypothesis posits that the human ability to run long distances is an adaptation that began roughly two million years ago. 

[Related: Humans are natural runners—and this ancient gene mutation might have helped .]

“Unlike other mammals, including other primates such as chimpanzees, humans can sweat profusely and have lower limb muscles evolved for stamina rather than power,” Morin and  Winterhalder say. “If economical and successful, endurance pursuits of medium-to-large game in a tropical environment could have [been] selected for that unique combination of traits: sweating and stamina.”

However, there have been few reports of contemporary humans using these endurance pursuits. Running long distances is generally viewed as energetically costly, and thus not worth it.

A game-hunting advantage

In their new study, Morin and Winterhalder studied roughly 400 recorded instances dating from the early 1500s to the early 2000s to investigate the role of endurance running while hunting. These included some first-hand accounts of different nomadic groups including the Evenki people in Siberia, the Innu in Canada, the Mbuti in the Democratic Republic of Congo, the Pitjantjatjara in Australia, the Inuit in Alaska, and more. Some of these ethnographic sources revealed that hunters sometimes ran over 62 miles in one pursuit. 

In addition to reviewing these accounts, the team used mathematical modeling to look at the various scenarios that could play out over a pursuit . They varied the size of the prey, how quickly or slowly a human pursued the animals (walking or running), and the distance covered.

The models found that in the right context, faster-paced endurance pursuit can increase energy returns. The models revealed that the calorific gains of endurance running were comparable to other hunting methods.

[Related: Why are humans good at endurance running? The answer is murky .]

“We were able to show that running or a mix of running and walking can be efficient, and it was a global practice by foragers prior to the modern era,” Morin and Winterhalder say. “In short, endurance pursuits would have provided hominins with an evolutionary advantage while competing with carnivores for game.”

The study suggests this type of hunting strategy would have been available to Pleistocene hominins (2.6 million to 11,700 years ago) and may also have had a role in human evolution. However, Morin and Winterhalder stress that this work does not speak directly to human’s evolutionary past, since it relies on ethnographic accounts from recent history.

Cultural bias

The team was surprised by the number of cases of long endurance pursuits that they found in environments that ranged from the bitter cold Canadian tundra to the more humid mountains of Hawaii. They also found that the study highlights a cultural bias in anthropology. 

“Committed recreational joggers and runners aside, Westerners tend to see running as ‘arduous,’ ‘costly,’ ‘challenging,’ and so on,” Morin and Winterhalder say. “In contrast, our observational data highlights Native societies that have encouraged and valued running, often for men, women and children, and in races and festive celebrations, as well as hunting.”

Morin and Winterhalder are currently working on another paper on endurance pursuits with more detail that assesses what may have motivated hunters and what seasons saw more endurance hunting. They are also working with collaborators Rebecca Bliege Bird and Doug Bird from Penn State on a study that will examine the division of labor in hunting.

Latest in Evolution

Chance or pattern stick insects show repeatable evolution in action chance or pattern stick insects show repeatable evolution in action, these monkeys have giant noses for exactly the reason you think these monkeys have giant noses for exactly the reason you think.

Scientists have replicated Earth's earliest form of evolution in the lab

• A minor theory of the creation of life just got a major boost in new experiments
• The 'RNA World' hypothesis proposed that Earth had RNA before life existed
• Scientists have now shown that RNA could have existed and evolved before life
• READ MORE: Did life start on Earth or in the stars? Scientists weigh in on theories

Scientists have been working for generations to untangle the mysteries of how life began on Earth, and one previously fringe theory just gained a lot of ground.

The 'RNA World' theory says that the so-called primordial soup of the early Earth was teeming with DNA's single-stranded sister RNA, which carries the instructions for sustaining life.

Now, a team of researchers at The Salk Institute have unlocked a crucial piece of that puzzle and even built it in the lab: an obscure but essential class of molecules called RNA polymerase ribozymes.

RNA polymerase ribozymes are not well understood, but scientists now suspect that these substances made it possible for RNA to not just replicate but actually evolve in the gel and muck of the early planet.

Even though little is known about RNA polymerase ribozymes, scientists know that they can copy strands of RNA.

In laboratory experiments, scientists showed that's not all they can do. 

Apparently they can evolve, as well.

Their experiments showed that RNA polymerase ribozymes can not only copy RNA but they can get better at doing it.

READ MORE: What is the 'RNA World' theory?

Life on Earth may have started thanks to a modified version of modern-day DNA's sister molecule that was integral to evolution 

Over time, they observed, the RNA polymerase ribozymes constructed copies of themselves could also copy RNA.

And the copies were not only functional, but in fact they got better at copying RNA - the same kind of evolution described by Charles Darwin.

As Darwin described evolution, the 'fitter' an organism is, the more likely it is to reproduce and pass on its genetic material.

He did not know about DNA, but DNA is how genes are passed on.

The new experiment suggests that a type of evolution may have been happening in the RNA World scenario.

As certain RNA polymerase ribozymes got better at copying RNA, they became more likely to stick around and keep performing their role.

Lower-quality ones, on the other hand, copied the RNA less reliably and their sequences drifted away, becoming more random over multiple courses of evolution. 

There may not have even been DNA to pass on, but evolution was happening, the authors of the new study said. 

'We're chasing the dawn of evolution,' said senior study author and Salk President Gerald Joyce in a statement. 

'By revealing these novel capabilities of RNA, we're uncovering the potential origins of life itself, and how simple molecules could have paved the way for the complexity and diversity of life we see today.'

The study was published in the journal Proceedings of the National Academy of Sciences . 

Eventually, RNA came together to form the more familiar double-stranded structure of DNA, giving rise to single-cell organisms and then more complex forms of life. 

These are all just theories, since we can never go back to the beginning of the planet and confirm how it all began.

But building RNA polymerase ribozymes in the lab and watching them help RNA evolve adds weight to the RNA World theory because it shows that this was theoretically possible. 

RNA is like the single-stranded version of DNA, and it contains the bits of genetic material that cells use to communicate.

Proteins, the basic materials of living things, are constructed using the instructions contained in RNA.

It's an unsung hero of life. It's always working, and we would die without it, but DNA tends to get the credit.

'We've long wondered how simple life was at its beginning and when it gained the ability to start improving itself,' said first study author Nikolaos Papastavrou, a research associate in Joyce's lab.

'This study suggests the dawn of evolution could have been very early and very simple. Something at the level of individual molecules could sustain Darwinian evolution, and that might have been the spark that allowed life to become more complex, going from molecules to cells to multicellular organisms.' 

Some scientists claim life was delivered on asteroids from the stars, while others say the building blocks for life came from space and assembled into lifeforms on Earth. An older idea argues that the basic molecules of life assembled themselves here on Earth from non-organic compounds.

Without RNA, most functions of the body would not be possible. RNA carries instructions on how to build proteins, which underlie almost everything cells do. 

Long before animals and single-cell organisms existed, the early Earth may have been home to strands of genetic material - and more importantly, the chemicals that can make them replicate.

Joyce and Papastavrou's team's work will need to be replicated by other researchers, but for now it represents a mark in favor of one theory for how life came to be. 

The team said they hope they can even discover how new RNA functions are invented through the same process of evolution.

• MyU : For Students, Faculty, and Staff

Clone of CSE welcomes 25 new faculty in 2023-24

STEM experts from across the world join the University of Minnesota 

The University of Minnesota College of Science and Engineering (CSE) welcomes 25 faculty members this 2023-24 academic year—on its way to achieving its goal to hire 60 faculty in three years.

The expertise of this new group of CSE researchers and educators is broad. They range in areas such as hybrid intelligence systems, the reconstruction of past environments and climates, electric machines and magnetic levitation, reinforced concrete structures, and mathematical models to predict the electronic properties of novel materials. 

Meet our new science and engineering faculty:

Rene Boiteau is an assistant professor of chemistry.  He joins Minnesota from Oregon State University, where he held a joint faculty appointment in the Pacific Northwest National Laboratory. Boiteau earned a bachelor’s in chemistry at Northwestern University, a master’s in earth sciences at University of Cambridge, and a Ph.D. in chemical oceanography at Massachusetts Institute of Technology and Woods Hole Oceanographic Institution. Much of his work is focused on developing analytical chemical approaches, especially mass spectrometry.

Zhu-Tian Chen is an assistant professor of computer science and engineering.  He received his bachelor’s in software engineering from South China University of Technology and Ph.D. in computer science from Hong Kong University of Science and Technology. Prior to Minnesota, Chen served as a postdoctoral fellow at Harvard University and postdoctoral researcher at the University of California San Diego. His recent work focuses on enhancing human-data and human-AI interactions in both AR/VR environments—with applications in sports, data journalism, education, biomedical, and architecture. 

Gregory “Greg” Handy  is an assistant professor of mathematics . He comes to Minnesota from the University of Chicago, where he was a postdoctoral scholar in the Departments of Neurobiology and Statistics. As an applied mathematician and theoretical biologist, Handy’s research strives to use biological applications as inspiration to create new mathematical techniques, and to combine these techniques with classical approaches to examine the mechanisms driving biological processes. This fall, he is teaching Math 2142: Elementary Linear Algebra.

Jessica Hoover is a professor of chemistry. She joins the University of Minnesota from West Virginia University, where she has been a faculty member since 2012. Hoover’s interest in catalysis has been the focus of her work since her undergraduate studies. She graduated with a bachelor’s from Harvey Mudd College before arriving at the University of Washington to pursue her Ph.D. She was a postdoctoral researcher at the University of Wisconsin, Madison.

Harman Kaur  is an assistant professor of computer science and engineering—and a University of Minnesota alumna  (2016 bachelor’s in computer science). Her research areas are human-centered artificial intelligence, explainability and interpretability, and hybrid intelligence systems. She is affiliated with the GroupLens Research Lab, a group of faculty and students in her department that’s focused on human computing interaction. Prior to Minnesota, Kaur served as a graduate researcher in the interactive Systems Lab and comp.social Lab at the University of Michigan, where she received both her master’s and Ph.D. 

Yulong Lu is an assistant professor of mathematics.  He joins the faculty from University of Massachusetts, Amherst. Lu received his Ph.D. in mathematics and statistics at the University of Warwick. His research lies at the intersection of applied and computational mathematics, statistics, and data sciences. His recent work is focused on the mathematical aspects of deep learning. This fall, Lu is teaching Math 2573H: Honors Calculus III to undergraduates and Math 8600: Topics in Applied Mathematics, Theory of Deep Learning to graduate students.

Ben Margalit is an assistant professor of physics and astronomy.  As a theoretical astrophysicist, he studies the fundamental physics of star explosions, collisions and other examples of intergalactic violence such as a black hole passing near a galaxy and “shredding it to spaghetti.” As part of his job, Margalit works closely with observational astronomers in selecting the kinds of places to look for transient events. He holds bachelor’s and master’s degrees from the Hebrew University of Jerusalem, and a Ph.D. from Columbia University. 

Maru Sarazola is an assistant professor of mathematics. She joins Minnesota from Johns Hopkins University, where she was a J.J. Sylvester Assistant Professor. Sarazola received her Ph.D. from Cornell University. Her research is focused on algebraic topology—specifically, her interest lies in homotopy theory (a field that studies and classifies objects up to different notions of "sameness") and category theory (“the math of math,” which looks to abstract all structures to study their behavior). This fall, she is teaching Math 5285H: Honors Algebra I. 

Eric Severson is an associate professor of mechanical engineering—and University of Minnesota alumnus  (2008 bachelor’s and 2015 Ph.D. in electrical engineering). He returns to his alma mater after being on the University of Wisconsin-Madison faculty for six years. Severson leads research in electric machines and magnetic levitation, with a renewed focus in addressing grand challenges in energy and sustainability through multidisciplinary collaborations. His interests include extreme efficiency, bearingless machines, flywheel energy storage, and electric power grid technology.

Kelsey Stoerzinger is an associate professor of chemical engineering and materials science. She was on the faculty at Oregon State University, with a joint appointment in the Pacific Northwest National Laboratory. She studies the electrochemical transformation of molecules into fuels, chemical feedstocks, and recovered resources. Her research lab designs materials and processes for the storage of renewable electricity. Stoerzinger holds a bachelor’s from Northwestern University, master’s from University of Cambridge, and Ph.D. from MIT.

Lynn Walker is a professor—and the L.E. Scriven Chair in the Department of Chemical Engineering and Materials Science.  Previously, she was on the faculty at Carnegie Mellon University. Her research focuses on developing the tools and fundamental understanding necessary to efficiently process soft materials and complex fluids. This expertise is being used to develop systematic approaches to incorporate sustainable feedstocks in consumer products. Walker holds a bachelor’s from the University of New Hampshire and Ph.D. from the University of Delaware. She was a postdoctoral researcher at Katholieke Universiteit Leuven in Belgium.

Alexander “Alex” Watson  is an assistant professor of mathematics—and former University of Minnesota postdoctoral researcher  in the School of Mathematics. Watson earned his Ph.D. at Columbia University. He works on mathematical models used to predict the electronic properties of materials, especially novel 2D materials such as graphene and twisted multilayer “moiré materials.” In summer 2022 and 2023, he presented at the U’s MathCEP Talented Youth Mathematics Program on topics related to materials research at the University of Minnesota. 

Anna Weigandt is an assistant professor of mathematics. She comes to Minnesota from the Massachusetts Institute of Technology, where she was an instructor. Weigandt completed her Ph.D. at the University of Illinois, and she was a postdoctoral assistant professor in the Center for Inquiry Based Learning at University of Michigan. She works in algebraic combinatorics, specifically Schubert calculus. This fall 2023, she is teaching Math 5705: Enumerative Combinatorics.

Michael Wilking is a professor of physics—and University of Minnesota alumnus (2001 bachelor’s in chemical engineering). He holds a master’s and Ph.D. from the University of Colorado. Prior to his return to the Twin Cities campus, Wilking served on the faculty at Stony Brook University. He completed his post-doc at TRIUMF, Canada's national particle accelerator center. Wilking was part of the Stony Brook research team honored with the 2016 Breakthrough Prize in Fundamental Physics.

Benjamin "Ben" Worsfold is an assistant professor of civil engineering —and a licensed professional engineer in both California and Costa Rica. His research interest lies in large-scale structural testing, finite element analysis of reinforced concrete structures, and anchoring to concrete. Worsfold earned his master’s and Ph.D. from the University of California, Berkeley, and bachelor’s from the University of Costa Rica.     

Yogatheesan Varatharajah is an assistant professor of computer science and engineering —and a visiting scientist in neurology at the Mayo Clinic. His research lies broadly in machine learning for health. Varatharajah earned his master’s and Ph.D. from the University of Illinois Urbana-Champaign. Prior to Minnesota, he was a research assistant professor of bioengineering at the University of Illinois and faculty affiliate for the Center for Artificial Intelligence Innovation with the National Center for Supercomputing Applications.

Starting in January 2024:

Emily Beverly is an incoming assistant professor of earth sciences. Prior to joining the University of Minnesota, she was on the faculty at University of Houston. She earned a bachelor’s from Trinity University, a master’s from Rutgers University, and a Ph.D. from Baylor University. Beverly was a postdoctoral researcher at Georgia State University and University of Michigan. Her research focuses on understanding environmental drivers of human and hominin evolution. Beverly uses stable isotopes and geochemistry to answer questions about past and future climates with a firm foundation in sedimentary geology and earth surface processes.

Alexander “Alex” Grenning is an assistant professor of chemistry.  He comes to Minnesota from the University of Florida, where he was a tenured faculty. Grenning earned a bachelor’s in chemistry and music from Lake Forest College, and a Ph.D. in organic chemistry from the University of Kansas. He was a postdoctoral researcher at Boston University. His work is focused on chemical synthesis and drug discovery.  

Yu Cao is an incoming professor of electrical and computer engineering. Prior to Minnesota, Cao was a professor at Arizona State University. He holds a bachelor’s in physics from Peking University and a master’s in biophysics plus a Ph.D. in electrical engineering and computer sciences from the University of California-Berkeley. His research includes neural-inspired computing, hardware design for on-chip learning, and reliable integration of nanoelectronics. Cao served as associate editor of the Institute of Electrical and Electronics Engineers’s monthly  Transactions on CAD .

Edgar Peña is an incoming assistant professor of biomedical engineering—and a University of Minnesota alumnus (2017 Ph.D. in biomedical engineering). He is a neuromodulation scholar who is interested in vagus nerve stimulation. Peña earned his bachelor’s degrees in electrical engineering and biomedical engineering from the University of California, Irvine. During his doctoral studies at the University of Minnesota Twin Cities, he used computational models to optimize deep brain stimulation.

Seongjin Choi is an incoming assistant professor of civil engineering.  He received his bachelor’s, master’s, and Ph.D. from the Korea Advanced Institute of Science and Technology. He was a postdoctoral researcher at McGill University. His work involves using data analytics to draw valuable insights from urban mobility data and applying cutting-edge AI technologies in the field of transportation.  

Pedram Mortazavi is an incoming assistant professor of civil engineering— and a licensed structural engineer in Canada .  His interests lie in structural resilience, steel structures, large-scale testing, development of damping and isolation systems, advanced simulation methods, and hybrid simulation. Mortazavi holds a bachelor’s from the University of Science and Culture in Iran, a master’s from Carleton University in Ottawa, and Ph.D. from the University of Toronto. 

Gang Qiu is an incoming assistant professor of electrical and computer engineering. He received his bachelor’s degree from Peking University in microelectronics and his Ph.D. in electrical and computer engineering from Purdue University. (He is currently a postdoctoral researcher at the University of California, Los Angeles.) Qiu’s research focuses on novel low-dimensional materials for advanced electronics and quantum applications. His current interest includes employing topological materials for topological quantum computing. 

Qianwen Wang is an incoming assistant professor of computer science and engineering. She received her bachelor’s from Xi’an Jiao Tong University and her Ph.D. from Hong Kong University of Science and Technology. Prior to Minnesota, Wang served as a post-doctoral researcher at Harvard University in the Department of Biomedical Informatics. As a visualization researcher, she created interactive visualization tools that enable humans to better interpret AI and generate insights from their data.

Katie (Yang) Zhao is an incoming assistant professor of electrical and computer engineering. Her research interest resides in the intersection between Domain-Specific Acceleration Chip and Computer Architecture. In particular, her work centers around enabling AI-powered intelligent functionalities on resource-constrained edge devices. Zhao received her bachelor’s and master’s from Fudan University, China, and Ph.D. from Rice University. (She is currently a postdoctoral researcher at Georgia Institute of Technology.)

Learn more about our goal to hire 60 new faculty in three years at the CSE recruiting website .

If you’d like to support faculty research in the University of Minnesota College of Science and Engineering, visit our  CSE Giving website .

Join our winning team

Our unique combination of science and engineering within one college in a vibrant, metropolitan area means more opportunities for you. Learn about faculty openings.

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