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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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Library of Congress Catalog Data: ISSN 1095-5054

The Evolution of Charles Darwin

A creationist when he visited the Galápagos Islands, Darwin grasped the significance of the unique wildlife he found there only after he returned to London

Frank J. Sulloway

From the nine times I have made the 5,000-mile journey to the Galápagos Islands, to follow in Charles Darwin’s footsteps, the most enduring impression I have gained is of life’s fragility. The minute a person steps off any of the tourist trails created by the Galápagos National Park Service and heads into the untamed interior of one of these islands, there is the risk of death under the intense, equatorial sun. On Santa Cruz Island, where the Charles Darwin Research Station is located, 17 people have disappeared since 1990. Most were subsequently found alive after having become hopelessly lost in dense underbrush and rugged volcanic terrain. But some perished. One was a young Israeli tourist who lost his way in Santa Cruz’s Tortoise Reserve in 1991. Amassive, two-month search failed to find him. In fact, some of the searchers themselves became lost and had to be rescued. In the end, fishermen discovered the young man’s body. A former Israeli tank commander, he had been in top physical condition, yet had managed to go only six miles before succumbing to the searing heat and lack of fresh water. A sign in the Tortoise Reserve says bluntly: “Stop. Do not go beyond this point. You could die.”

This is the deceptively treacherous world of sun-baked lava, spiny cactus and tangled brushwood into which Charles Darwin stepped in September 1835, when he reached the Galápagos Islands with fellow crew members of the HMS Beagle. The Beagle’s captain, Robert FitzRoy, described the barren volcanic landscape as “a shore fit for Pandemonium.” At 26, Darwin had come to the archipelago, which straddles the Equator some 600 miles west of Ecuador, as part of the Beagle’s five-year mission to survey the coast of South America and to conduct a series of longitudinal measurements around the globe. Darwin’s five-week visit to these remarkable islands catalyzed the scientific revolution that now bears his name.

Darwin’s revolutionary theory was that new species arise naturally, by a process of evolution, rather than having been created—forever immutable—by God. According to the well-established creationist theory of Darwin’s day, the exquisite adaptations of many species—such as the hinges of the bivalve shell and the wings and plumes on seeds dispersed by air—were compelling evidence that a “designer” had created each species for its intended place in the economy of nature. Darwin had wholeheartedly accepted this theory, which was bolstered by the biblical account in Genesis, until his experiences in the Galápagos Islands began to undermine this way of thinking about the biological world.

The Galápagos Islands were formed by volcanic eruptions in the recent geological past (the oldest of the islands emerged from the ocean just three million years ago), and Darwin realized that the remote setting must have presented life with a new beginning. “Seeing every height crowned with its crater, and the boundaries of most of the lava-streams still distinct, we are led to believe that within a period, geologically recent, the unbroken ocean was here spread out,” he wrote in his Journal of Researches. “Hence, both in space and time, we seem to be brought somewhat near to that great fact—that mystery of mysteries—the first appearance of new beings on this earth.”

How, Darwin asked himself, had life first come to these islands? “The natural history of these islands,” he later pointed out, “is eminently curious, and well deserves attention. Most of the organic productions are aboriginal creations, found nowhere else.” Yet all of the creatures showed a marked relationship with those from the American continent. The novel Galápagos species, Darwin reasoned, must have started out as accidental colonists from Central and South America and then diverged from their ancestral stocks after arriving in the Galápagos. As he traveled from island to island, Darwin also encountered tantalizing evidence suggesting that evolution was proceeding independently on each island, producing what appeared to be new species.

Other evidence, from the South American continent, showed that species did not seem to be stable across either geographic space or the deep reaches of paleontological time. But the particularly compelling evidence from the Galápagos Islands catapulted Darwin and life science into the modern age. He subsequently added to his daring endorsement of evolution the crucial insight that species evolve by means of natural selection: variants that are better adapted to their environments are more likely to survive and reproduce. When he finally published On the Origin of Species by Means of Natural Selection in 1859, Darwin’s revolutionary theories not only recast the study of life but also turned the Galápagos Islands into hallowed scientific ground.

More than three decades ago, I became fascinated by Darwin’s life, and especially by his historic voyage around the world. When evolutionary biologist Edward O. Wilson, whose undergraduate course I was taking at Harvard, learned of my interest, he suggested that I go to the Galápagos Islands, and he helped fund a documentary about Darwin’s voyage. My first trip, in 1968, was two years before the beginning of organized tourism in the Galápagos. Just getting to the islands was a challenge. Our expedition flew from Guayaquil, Ecuador, in a PBY, an amphibious, twin-engine patrol plane dating back to the World War II era. We sat in seats made of mesh nets. There were numerous holes in the plane’s undercarriage, through which I could see all the way to the ocean below. The impression these starkly beautiful islands made upon me was indelible (the volcano that forms the island of Fernandina put on a spectacular eruption during our visit).

Eight expeditions later, I continue to be drawn to these islands in an effort to document their extraordinary impact on Darwin, as well as to study ecological changes since Darwin’s day. With the advent of organized tourism, much has changed. Now, two to four passenger planes fly each day to the Galápagos, bringing a total of about 100,000 tourists a year. Puerto Ayora, home to the Charles Darwin Research Station, is a booming tourist stop with a population of about 15,000 people, almost ten times the number that resided there during my first visit. As tourists enjoy their organized cruises around the islands, they are confined to 60 localities, carefully selected by the National Park Service, and are required to stay on clearly marked paths that keep them out of harm’s way.

Two main questions confront the student of Darwin’s historic visit: Where did Darwin go, and exactly how did his visit affect his scientific thinking? Answering the first turns out to be easier than one might think, thanks to a rich repository of documentary sources. The British Navy had a penchant for keeping detailed records, and the Beagle’s voyage is described in three ship’s logs, Captain FitzRoy’s personal narrative, a series of excellent maps made by the Beagle’s officers, and various watercolors and sketches by crew members. We are also able to draw on Darwin’s own extensive record of his dozen or so field trips, which encompasses more than 100 pages of unpublished notes and more than 80 pages of published material.

For five years the Beagle’s logs recorded, often on an hourly basis, where the ship was and what it was doing. Two days after the first sighting of land in the Galápagos, on September 15, 1835, the Beagle anchored in Stephens Bay on Chatham Island, now known as San Cristóbal. (All the islands were given Spanish as well as English names by their early visitors, who included Spaniards seeking Inca gold and silver in Peru, and British buccaneers intent on stealing these riches from the Spanish.) From this anchorage, the Beagle officers recorded a bearing of N10ºE to Kicker Rock, an impressive 470-foot islet about four miles off the shore, and a bearing of N45ºE to Finger Hill, a 516-foot tuff crater. When drawn on a map, the place at which these two bearings cross indicates the Beagle’s point of anchorage. Using other bearings in the Beagle’s logs, together with Darwin’s remarks in his diary and scientific notes, it is possible to reconstruct virtually all of Darwin’s landing sites and inland treks during his five-week visit. These include many regions that are either in remote or potentially dangerous locations and hence off limits to tourists.

As the Beagle sailed from east to west through the archipelago, Darwin visited four of the larger islands, where he landed at nine different sites. On San Cristóbal, Darwin was particularly drawn to a heavily “Craterized district” on the rugged, northeastern coast. “The entire surface of this part of the island,” Darwin reported, “seems to have been permeated, like a sieve, by the subterranean vapours: here and there the lava, whilst soft, has been blown into great bubbles; and on other parts, the tops of caverns similarly formed have fallen in, leaving circular pits with steep sides. From the regular form of the many craters, they gave to the country an artificial appearance, which vividly reminded me of those parts of Staffordshire, where the great iron-foundries are most numerous.”

As Darwin explored San Cristóbal, he encountered many birds and animals new to him. He marveled at the remarkable tameness of the birds, pushing a curious hawk off a branch with the barrel of his gun, and trying to catch small birds with his hands or in his cap. He also noted the striking dominance of reptiles within these islands, which made the archipelago seem like a journey back in time. On the shoreline were swarms of “hideous-looking” marine iguanas—the world’s only oceangoing lizards. On land, the Beagle crew encountered large land iguanas, closely allied to their marine cousin; a couple of smaller lizards; a snake; and giant land tortoises, after which the islands are named. (The old Spanish word galápago means saddle, which the shape of the tortoise’s carapace resembles.)

In the midst of a partly vegetated lava field on San Cristóbal, Darwin came upon two enormous tortoises, each weighing more than 200 pounds. One, he noted, “was eating a piece of cactus, and as I approached it, it stared at me and slowly stalked away; the other gave a deep hiss, and drew in its head. These huge reptiles, surrounded by the black lava, the leafless shrubs, and large cacti, seemed to my fancy like some antediluvian animals.” Altogether these giant reptiles contributed dramatically, Darwin thought, to the “strange Cyclopean scene.”

Floreana was the next of the four islands Darwin visited. The first settlement in the Galápagos had been established there just three years before, populated by convicts from Ecuador; it collapsed a few years later, after some malcontented prisoners took up arms against the local governor. On Floreana, Darwin remarked in his private diary, “I industriously collected all the animals, plants, insects, & reptiles from this Island”—adding, “It will be very interesting to find from future comparison to what district or ‘centre of creation’ the organized beings of this archipelago must be attached.” Still thinking like a creationist, Darwin was seeking to understand the islands’ strange inhabitants within the ruling biological paradigm.

After a brief stop at Tagus Cove, on Isabela, the Beagle headed for Santiago. Darwin, three crew members and his servant, Syms Covington, were left for nine days to collect specimens while the Beagle returned to San Cristóbal to obtain fresh water. Guided by a settler from Floreana who had been sent to hunt tortoises, Darwin ascended to the highlands twice to collect specimens in the humid zone. There he was able to study, in considerable detail, the habits of the tortoise. These lumbering behemoths, he found, came from all over the island to drink water at several small springs near the summit. Hordes of the giants could be seen coming and going, with necks outstretched, burying their heads in the water, “quite regardless of any spectator,” to relieve their thirst. Darwin counted the number of times that the tortoises swallowed in a minute (about ten), determined their average speed (six yards a minute), and studied their diet and mating habits. While in the highlands Darwin and his companions dined exclusively on tortoise meat. He commented that it was very tasty when roasted in the shell or made into soup.

When he was not collecting specimens, Darwin devoted time to trying to understand the islands’ geological features, especially the prominent tuff cones near his campsite at Buccaneer Cove. He was the first geologist to appreciate that such sandstone-like structures, which rise to a height of more than 1,000 feet, owe their peculiar features to submarine eruptions of lava and mud; they mix at high temperatures with seawater, producing tiny particles that shoot into the air and rain down on the land to form huge cinder cones.

On October 17, Darwin and his four Santiago companions reboarded the Beagle with their week’s haul of specimens. The ship spent the next two days completing a survey of the two northernmost islands and then, 36 days after arriving in the archipelago (during which he spent 19 days on land), the Beagle sailed for Tahiti. Although Darwin did not yet fully appreciate it, a revolution in science had begun.

Following in Darwin’s path, one understands hardships that he overcame that are not readily apparent to readers of his publications. Trekking in the Galápagos, everything is dictated by how much water one can carry, which limits each excursion to about three days—or, for longer excursions, requires stashing food and water along a route.

To Darwin, such logistics would have been even more problematic, as he did not have the lightweight equipment, such as aluminum-frame backpacks and plastic water containers, that we have today. Assisted by his servant, Darwin would have brought his geological hammer, a clinometer for measuring inclines, a shotgun for collecting birds, a compass, plant presses, rodent traps, specimen bottles, spirits of wine for preserving invertebrates, a notebook, a sleeping bag, food and, of course, water. With a characteristic understatement (reflecting perhaps his excellent physical conditioning after extensive fieldwork in South America during the previous four years), Darwin wrote of the 3,000-foot climb to the summit of Santiago merely that the walk was “a long one.” During our own climb along this route in 2004, when we were all packing about 70 pounds, one of my expedition companions was so overcome with heat exhaustion that he had to return to our base camp in Buccaneer Cove; another sprained his ankle on the treacherous footing but managed to keep going.

During a previous expedition, I and five companions came to appreciate, much more vividly than we would have liked, Darwin’s comparison of Galápagos lava flows to an imagined scene from the “Infernal regions.” We were on Santiago, where Darwin had camped for nine days, on our way to a region where tortoises could sometimes be found. Our two guides had suggested a shortcut across a coastal lava flow. What none of us could see from the vantage point of our boat’s landing site was that our route involved more than eight miles of almost continuous lava rock—not just the mile or two that our guides had led us to expect. As we began our trek across this perilous field of jagged lava, we had no idea how close to death we would all come. What was supposed to be a 6-hour excursion became a 51-hour nightmare as we climbed over jumbled piles of blocks with razor-sharp edges, and in and out of steep ravines formed by meandering lavas and collapsed lava domes. Such flows, commented Darwin, who ventured onto several smaller ones, were like “a sea petrified in its most boisterous moments.” He added, “Nothing can be imagined more rough or horrid.”

During our second day on that Santiago lava flow, our water ran out. To make matters worse, our two guides had failed to bring any water of their own and were drinking ours. By the afternoon of the third day we were all severely dehydrated and were forced to abandon most of our equipment. In desperation, our guides hacked off a candelabra cactus branch, and we resorted to drinking the juice, which was so bitter that I retched. Before we finally made it to the coast, where a support vessel was frantically looking for us, one member of the expedition was delirious and close to death. He was subsequently hospitalized for five days, back in the United States, and it took him more than a month to recover.

On another occasion I accompanied Charles Darwin Research Station botanist Alan Tye on a search for the rare Lecocarpus shrub, which Darwin had collected in 1835. A member of the daisy family, the plant had not been seen by anyone in a century, causing some botanists to question Darwin’s reported locality. The day was unusually hot, and Tye, after a few hours of hiking, felt the onset of heat exhaustion and asked me to take over the lead. Using a machete to help clear our way through the brush, I too became heat exhausted, and began to vomit. Heat exhaustion turned out to be the least of my problems. I had inadvertently cut the branch of an overhanging manzanillo tree, whose apples are poison to humans but beloved by tortoises. Some of the tree’s sap had gotten onto a wristband I was wearing and then into both of my eyes. The sting from the sap was almost unbearable, and dousing my eyes with water did nothing to help. For the next seven hours I was nearly blinded and could open my eyes for only a few seconds at a time. As I walked back to our campsite, five hours away, I often had to balance, with my eyes shut, on huge boulders in a dry riverbed, and on the edge of lava ravines. Those were the most painful seven hours I have ever spent. Fortunately, Tye and I did find the rare plant we had been seeking, resolving a century-old mystery and establishing that San Cristóbal has two different members of the same Lecocarpus genus.

Darwin personally reported no untoward physical difficulties during his own Galápagos visit, although he and four companions on Santiago did complain about a shortage of fresh water and the oppressive heat, which reached 137 degrees Fahrenheit (the maximum on their thermometer), as measured in the sandy soil outside their tent. Darwin was twice reminded of the potentially lethal outcome of any excursion into the Galápagos wilds. The Beagle’s crew encountered one lost soul, from the American whaler Hydaspy, who had become stranded on Española, and this stroke of good fortune saved his life. Also, Captain FitzRoy recorded that another sailor from an American whaler had gone missing and that the whaler’s crew was out looking for him. One should not be surprised, then, that, while he was engaged in fieldwork, Darwin would have focused his attention substantially on surviving the many hazards of the Galápagos.

Legend has it that Darwin was converted to the theory of evolution, eureka-like, during his visit to the islands. How could he not have been? In retrospect, the evidence for evolution seems so compelling. Darwin tells us in his Journal of Researches, first published in 1839, that his fascination with the “mystery of mysteries”—the origin of new species—was first aroused by a chance discussion on Floreana with Nicholas Lawson, the vice governor of the islands. Based in part on differences in the shape of a tortoise’s shell, Lawson claimed that “he could at once tell from which island any one was brought.” Darwin also noticed that the mockingbirds seemed to be either separate varieties or species on the four islands he visited. If true, he speculated, “such facts would undermine the stability of Species”—the fundamental tenet of creationism, which held that all species had been created in their present, immutable forms.

Darwin’s first reflections about evolution were an afterthought, written during the last leg of the Beagle voyage, nine months after his Galápagos visit. (I owe this historical insight to a curious fact—Darwin was a lousy speller. In 1982 I was able to date Darwin’s earliest and previously undated writings about possible species transformations by analyzing changes in Darwin’s pattern of misspellings during the voyage.) While in the Galápagos, Darwin was far more interested in the islands’ geology than their zoology. We know, moreover, from the complete record of his unpublished scientific notes that he was personally dubious about evolution. For nearly a year and a half following his Galápagos visit, he believed that the tortoises and mockingbirds were probably “only varieties,” a conclusion that did not threaten creationism, which allowed for animals to differ slightly in response to their environments. According to creationist theory, species were a bit like elastic bands. The environment could induce variation, but the inevitable pull of the immutable “type”—which was thought to be an idea in the mind of God—caused species to revert to their original forms. For the creationist, all variation from the “type” was limited by an impassable barrier between true species.

Darwin’s initial failure to appreciate the case for evolution stems in large part from a widely mistaken assumption about the tortoises. Naturalists thought that giant tortoises had been introduced to the Galápagos by buccaneers who had transported them from the Indian Ocean, where similar tortoises are present on several islands. This confusion explains Darwin’s astonishing failure to collect even a single specimen for scientific purposes. He and his servant did take back to England, as pets, two baby tortoises. Those juvenile tortoises further misled Darwin, because differences among subspecies are evident only in adults. Not realizing the importance of tortoises for the theory he would eventually develop about the origins and diversity of living things, Darwin and his fellow shipmates ate their way through 48 adult tortoise specimens and threw their shells overboard.

Darwin’s famous finches also misled him at first. There are 14 finch species in the Galápagos that have all evolved from a single ancestor over the past few million years. They have become one of the most famous cases of species adapting to different ecological niches. From Darwin’s specimen notebooks, it is clear he was fooled into thinking that some of the unusual finch species belonged to the families they have come to mimic through a process called convergent evolution. For example, Darwin thought the cactus finch, whose long, probing beak is specialized for obtaining nectar from cactus flowers (and dodging cactus spines), might be related to birds with long, pointed bills, such as meadowlarks and orioles. He also mistook the warbler finch for a wren. Not realizing that all of the finches were closely related, Darwin had no reason to suppose that they had evolved from a common ancestor, or that they differed from one island to another.

My own discovery, more than 30 years ago, that Darwin had misidentified some of his famous Galápagos finches led me to the Darwin Archive at Cambridge University Library, in England. There I found a manuscript trail that poked further holes in the legend that these birds precipitated an immediate “aha” moment. It was only after Darwin’s return to England, when experts in herpetology and ornithology began to correct his Galápagos reports, that he realized the extent of his collecting oversights and misidentifications. In particular, Darwin had failed to label most of his Galápagos birds by island, so he lacked the crucial evidence that would allow him to argue that different finch species had evolved separately while isolated on different islands of the Galápagos group.

Five months after his return to England, in March 1837, Darwin met with ornithologist John Gould. Five years older than Darwin, Gould was just beginning to become known for his beautifully illustrated monographs on birds, which today are highly prized collectors’ items. One of my most unexpected discoveries in the Darwin archives was the piece of paper on which Darwin recorded his crucial meeting with Gould. This manuscript clearly shows how Darwin’s thinking began to change as a result of Gould’s astute insights about the Galápagos birds. Unlike Darwin, Gould had instantly recognized the related nature of the Galápagos finches, and he also persuaded Darwin, who questioned him closely on the subject, that three of his four Galápagos mockingbirds were separate species rather than “only varieties.” Gould also informed Darwin that 25 of his 26 land birds from the Galápagos were new to science, as well as unique to those islands.

Gould’s taxonomic judgments finally caused Darwin to embrace the theory of evolution. Stunned by the realization that evolving varieties could break the supposedly fixed barrier that, according to creationism, prevents new species from forming, he quickly sought to rectify his previous collecting oversights by requesting island locality information from the carefully labeled collections of three Beagle shipmates. Two of these collections, by Captain FitzRoy and FitzRoy’s steward, Harry Fuller, contained 50 Galápagos birds, including more than 20 finches. Even Darwin’s servant, Covington, had done what Darwin had not, labeling by island his own personal collection of finches, which were later acquired by a private collector in England. The birth of the Darwinian revolution was a highly collaborative enterprise.

The case for evolution presented by this shared ornithological evidence nevertheless remained debatable for nearly a decade. Darwin was not entirely convinced Gould was right that all the finches were separate species, or even that they were all finches. Darwin also knew that, without specimens in hand, island-to-island differences among the tortoises were contestable, even though a French herpetologist told a delighted Darwin in 1838 that at least two species of tortoise existed in the islands.

In 1845 Darwin’s botanist friend Joseph Hooker gave Darwin the definitive evidence he needed to support his theory. Hooker analyzed the numerous plants that Darwin had brought back from the Galápagos. Unlike the birds, the plants all had accurate localities attached to them—not because Darwin had collected the plants with evolutionary theory in mind, but because plants have to be preserved in plant presses shortly after being collected. Hence the specimens from each island had all been pressed together, rather than being intermixed. Hooker eventually identified more than 200 species, half of which were unique to the Galápagos. Of these, three-quarters were confined to single islands—yet other islands often possessed closely related forms also found nowhere else on earth. At last, Darwin had the kind of compelling evidence that he felt he could really trust. As he wrote to Hooker: “I cannot tell you how delighted & astonished I am at the results of your examination; how wonderfully they support my assertion on the differences in the animals of the different islands, about which I have always been fearful.”

It is certainly testimony to Darwin’s intellectual boldness that he had conceived of the theory of evolution some eight years earlier, when he still harbored doubts about how to classify Galápagos tortoises, mockingbirds and finches. To bolster the unorthodox theory, he engaged in an exhaustive, 20-year program of research that ultimately became so convincing that he did not need the inspirational Galápagos evidence to make his case. As a consequence, Darwin devotes only 1 percent of the Origin of Species to the Galápagos, barely more than he allotted to the Madeiras Islands or New Zealand.

I have often wondered why Darwin, prior to the publication of Origin of Species in 1859, was the only person known to have become an evolutionist based on evidence from the Galápagos —especially after Hooker’s compelling botanical study. After all, Captain FitzRoy, John Gould, Joseph Hooker and numerous scientific specialists who helped Darwin with the analysis and publication of his voyage findings were fully aware of the unusual nature of his Galápagos collections. In the end, it is perhaps a question of courageous willingness to consider new and unconventional ways of thinking. When Darwin’s uncle, Josiah Wedgwood, was trying to convince Darwin’s father that young Charles should be allowed to sail on the Beagle, Josiah noted Charles was “a man of enlarged curiosity.”

One repeatedly sees the truth of Wedgwood’s observation. Charles Darwin’s undeniable knack for asking the right questions, bolstered by his five-week visit to an extraordinary workshop of evolution brimming with unasked and unanswered questions, ultimately precipitated the Darwinian revolution. In posing novel questions, Darwin voyaged back to the Galápagos Islands again and again in his mind, reassessing his imperfect evidence in the light of his maturing theory and benefiting from new and better evidence obtained by other researchers.

Although much of what one sees in the Galápagos today appears to be virtually identical to what Darwin described in 1835, the biology and ecology of the islands have been substantially transformed by the introduction of exotic plants, insects and animals. Completely gone from Santiago, for example, are the golden-colored land iguanas, described as so numerous by Darwin in 1835 that “we could not for some time find a spot free from their burrows, on which to pitch our tent.” The principal culprits in this extinction, besides Beagle crew members and other people who found these iguanas very good eating, were the rats, dogs, cats, goats and pigs introduced by mariners and would-be settlers who left their animals to run wild. Along with visiting whalers, early settlers also hunted the giant land tortoises to extinction on some islands, and they nearly wiped them out on other islands. Recently introduced insects and plants—including fire ants, wasps, parasitic flies and quinine trees—have also become highly invasive and threaten the Galápagos ecosystem.

When I first visited the Galápagos, 37 years ago, quinine was not yet a serious problem, and feral goats, which later invaded Isabela’s Volcán Alcedo (home to about 5,000 giant land tortoises), had yet to reach epidemic numbers. But by the 1990s, more than 100,000 goats were devastating the volcano’s vegetation. Darwin himself would doubtless have applauded the indefatigable efforts of the Charles Darwin Research Station and the National Park Service to stem the tide of destruction to the fragile ecosystem, and he would also have marveled at some of the occasional success stories, such as the recent eradication of feral pigs from Santiago.

From the many times I have followed in Darwin’s footsteps to better understand his voyage of discovery, I have come to believe that the Galápagos continue to epitomize one of the key elements of Darwin’s theories. As he argued, over long periods of time natural selection is ultimately responsible for the “endless forms most beautiful and most wonderful” around us. Empowering this evolutionary process on a day-to-day basis is what Darwin termed “the struggle for existence.” This evolutionary engine works its slow but unrelenting biological effects primarily through accidents, starvation and death. Perhaps nowhere else is this harsh biological principle more evident than in the strange islands that inspired Darwin’s scientific revolution.

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• Darwinian Essays
• Open access
• Published: 06 December 2008

Charles Darwin and Human Evolution

• Ian Tattersall 1  

Evolution: Education and Outreach volume  2 ,  pages 28–34 ( 2009 ) Cite this article

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Along with his younger colleague Alfred Russel Wallace, Charles Darwin provided the initial theoretical underpinnings of human evolutionary science as it is practiced today. Clearly, nobody seeking to understand human origins, any more than any other student of the history of life, can ignore our debt to these two men. As a result, in this bicentennial year when Darwin’s influence in every field of biology is being celebrated, it seems reasonable to look back at his relationship to paleoanthropology, a field that was beginning to take form out of a more generalized antiquarian interest just as Darwin was publishing On the Origin of Species in 1859. Yet there is a problem. Charles Darwin was curiously unforthcoming on the subject of human evolution as viewed through the fossil record, to the point of being virtually silent. He was, of course, most famously reticent on the matter in On The Origin of Species , noting himself in 1871 that his only mention of human origins had been one single throwaway comment, in his concluding section:

“light will be thrown on the origin of man and his history” (Darwin 1859 , p. 488).

This has, of course, to rank among the most epic understatements ever. And of course, it begged the question, “what light?” But in the event, Darwin proved highly resistant to following up on this question. This is true even of his 1871 book The Descent of Man, and Selection in Relation to Sex in which Darwin finally forced himself to confront the implications of his theory for the origin of humankind, and the main title of which is in many ways something of a teaser.

There were undoubtedly multiple reasons for this neglect of the issue that was naturally enough in the back of everyone’s mind when reading The Origin , let alone The Descent of Man . First, and most famously, there was the intellectual and social milieu in which Darwin lived. During the second quarter of the nineteenth century, during which Darwin’s most formative experiences all occurred, England was at one level a place of intense political and social ferment. The Reform Act of 1832 had witnessed significant changes in the way Parliament was elected; the New Poor Law of 1834 had at least recognized problems in the system of poverty relief; and the founding of London University in 1826 had provided, at last, a secular alternative to the fusty Anglican Universities of Cambridge and Oxford. But despite all this, early Victorian England remained a strait-laced Anglican society whose upper classes, well remembering events in France not so long before, had little taste for radical ideas in any field.

In such an unreceptive milieu, the retiring Darwin had little relish for stirring things up with radical ideas on human emergence. He had originally planned to include mankind in the “Big Book” he was working on when spurred by Wallace into writing and publishing its “abstract” in the form of On the Origin of Species (Moore and Desmond, 2004 ). But despite having then made the conscious decision to avoid the vexatious and contentious issue of human evolution in On the Origin of Species , he still saw his book widely condemned as intellectual heresy, even as a recipe for the ruin of established society. As a result, while contemplating the publication of The Descent of Man a decade later, Darwin was still able to write to a colleague that:

“When I publish my book, I can see that I shall meet with universal disapprobation, if not execution” (in a letter to St. George Mivart, April 23, [probably] 1869).

As the least combative of men, Darwin dreaded the response he knew that any attempt to stake out a position on human origins would receive. And to be quite frank, given all his hesitations, it is not at all clear to me exactly why Darwin felt so strongly impelled to publish The Descent of Man or at least to have given it the provocative if not quite accurately descriptive title he did.

One possibility is merely that, during the 1860s, such luminaries as Alfred Russel Wallace, Ernst Haeckel, and Thomas Henry Huxley had all publicly tackled the matter of human origins and not invariably to Darwin’s satisfaction. As a result, Darwin may simply have felt it necessary to make his own statement on the matter, come hell or high water, in a decade that was already significantly more receptive to evolutionary notions than the 1850s had been. As to why it was so important to him to see it written, the Darwin historians James Moore and Adrian Desmond have pointed to an agenda that did not translate directly from Darwin’s stated desire simply:

“to see how far the general conclusions arrived at in my former works were applicable to man… all the more desirable as I had never applied these views to a species taken singly” (Darwin 1871 , ii, p. 2).

There was clearly more to it than that, and Moore and Desmond emphasize that Darwin came from a family of free-thinkers. He was the grandson both of the libertarian poet and physician Erasmus Darwin and of the Unitarian Josiah Wedgwood who had, in 1787, produced the famous “am I not a man and a brother?” cameo that became the emblem of the movement to abolish slavery. What is more, at a very impressionable age, Charles had attended the more or less secularist Edinburgh University in Scotland. There he had studied under the anatomist Robert Grant who quoted Lamarck with approval; and there also he was taught taxidermy by John Edmondston, a freed slave from British Guiana for whom he developed very considerable respect.

From the very beginning, then, Darwin abhorred slavery; and he was already a convinced abolitionist by the time he boarded the Beagle in 1831 for his formative round-the-world voyage. His subsequent experiences in Brazil, where he witnessed hideous cruelties being inflicted on slaves, and in Argentina, where he saw the pampas Indians being slaughtered to make way for Spanish ranchers, only confirmed him in his egalitarian beliefs. This concern linked in with Darwin’s strong views on the unity of mankind. In the early and middle nineteenth century, this was a very hot topic in the English-speaking world, even “the question of the day,” as the blurb to a book by the Presbyterian abolitionist Thomas Smyth ( 1850 ) put it.

The precise question at issue was of course whether the races of mankind had been separately created (or even, after The Origin of Species was published, descended from different species of apes), as the proslavery polygenists proposed; or whether they were simply varieties of one single species, as proclaimed by the antislavery monogenists.

In this matter, there was little hope that science could ever be disentangled from politics; and it was this, above anything else, it seems, that had dissuaded Darwin from including humans in On the Origin of Species . By 1871, however, the world had changed enough to allow Darwin to contemplate entering the fray; and there is substantial reason for viewing The Descent of Man as Darwin’s contribution on the monogenist side to the monogenism versus polygenism debate—although Moore and Desmond ( 2004 ) make a strong argument that, in the end, it became at least as important to Darwin as a showcase for his notion of sexual selection.

Indeed, these two aspects could hardly be separated, since sexual selection—in other words, mate choice—was Darwin’s chosen mechanism to explain:

“the divergence of each race from the other races, and all from a common stock” (Darwin 1871 , ii, p. 371).

And most of the book is, in true Darwinian style, taken up with hugely detailed documentation of sexual selection among organisms, in support of the proposition that humankind was simply yet another product of Nature, albeit with many of its peculiar features governed by mate choice rather than by adaptiveness.

Still, Darwin had chosen to title his book The Descent of Man . And “descent” was a word that he had long used as equivalent to “ancestry.”

Given which, it seems at the least a bit odd that in the entire two volumes of the first edition of the work only passing consideration at best is given to those fossils that might have given a historical embodiment to the notion of human emergence. Even when Darwin wrote the Origin in 1858–1859, a handful of “antediluvian” human fossils was already known. The most famous of these was the skullcap and associated bones discovered in 1856 in the “Little Feldhofer Grotto,” a limestone cave in the Neander Valley, near Dusseldorf in Germany. This fossil, associated with the bones of mammal species now extinct, was destined in 1863 to become the type specimen of Homo neanderthalensis , now known to be an extinct cousin of our own species, Homo sapiens . But it was not published until 1858, barely a year before the Origin appeared; and even then, it was described in German, in a rather obscure local scientific journal, making it highly unlikely that the Neanderthal fossil came to Darwin’s attention before Hermann Schaaffhausen’s work on it was translated into English by the London anatomist George Busk in 1861. Still, this was an entire decade before The Descent of Man first appeared, which makes it a little odd that the detail-obsessed Darwin made virtually no reference to the Feldhofer fossil in a book which one might have expected to find it at front and center or at least introduced as a phenomenon to be explained. Only in passing did he mention it at all.

The neglect of the Neanderthal fossil is all the more remarkable in light of the fact that, in 1863, George Busk had already described another individual, of similarly distinctive appearance, from the British possession of Gibraltar. Taken together, these two specimens had demonstrated pretty conclusively by the mid-1860s that here was not simply a pathological form of Homo sapiens , as many influential biologists had claimed, but at the very least a highly distinctive human “variety” that needed explanation of some kind. In sharp contrast to any modern human fossils then known from anywhere in the world, the Neanderthal skull was very long and low. What’s more, it terminated in front in prominent brow ridges that arced individually above each eye and at the rear in a curious bulge that became known as a “chignon” or “bun.” On the other side of the balance, this skull had evidently contained a brain that was equal in size to the brain that resided in the heads of modern people. Either way, it was obviously an important fossil.

Yet the only reference that the astonishingly erudite Darwin made to this fossil, in almost 800 pages of dense text, was in the context of a throwaway admission that:

“some skulls of very high antiquity, such as the famous one of Neanderthal, are well developed and capacious.” (Darwin 1871 , i, p. 140).

It is hard not to conclude that, in limiting his reference to the Feldhofer in this way, Darwin was grasping at the politically congenial notion that the Neanderthaler, ancient as it was, was simply a bizarre kind of modern human. For perhaps more remarkably yet, nowhere in The Descent of Man did Darwin directly confront the idea that the human species might even in principle have possessed extinct relatives—despite the fact that the entire Origin of Species is suffused with the notion that having extinct relatives must be a general property of all living forms.

In his introduction to The Descent , Darwin partially excused himself for only passing reference to human antiquity by deferring to the work of Jacques Boucher de Perthes, Charles Lyell, his protégé Sir John Lubbock, and others. But there was very likely another key to Darwin’s reluctance to embroil himself too closely with the actual tangible evidence for human ancientness and ancestry. For the 1860s, the years leading up to the publication of the Decent of Man , were a period of rampant fraud and fakery in the antiquities business—and a business it certainly was. By the time Darwin published the Descent , it was widely accepted that, at the very least, the human past far antedated Biblical accounts. And an energetic search was on for evidence of that ancient past, with wealthy dilettantes pouring money into excavations all across Europe. Today, we honor the French antiquarian and customs-collector, Boucher de Perthes, as the first man to recognize the Ice Age stone handaxes found in the terraces of the Somme River as the products of truly ancient humans. But in the 1840s and 1850s, Boucher de Perthes was widely ridiculed as the gullible victim of hoaxers; and indeed, it is true that he was entirely undiscriminating in what he was prepared to consider ancient. Many of his prize artifacts turned out later to have been knapped by his quarrymen, who were only too happy to con their employer out of a few francs. Indeed, there is a charming story of a lady who asked a local peasant what he was doing chipping away at a piece of flint and was told: “Why, I am making Celtic handaxes for Monsieur Boucher de Perthes.” “Celtic” was then the current term for anything prehistoric.

Of course, Boucher de Perthes was not alone. For profitable deception of the gentry, by clever tricksters from the underclasses, was a rather sporting component of class warfare all across Europe in the mid—nineteenth century. But Boucher de Perthes had, in particular, been embroiled in a famous hoax involving a supposedly antediluvian human fossil (Trinkaus and Shipman 1993 ). In early 1863, he offered a reward of 200 francs to any workman who could find the remains of the maker of his ancient stone tools. And on March 28 of that year, a supposedly ancient human jawbone duly showed up, along with handaxes, at a site called Moulin-Quignon. A scandal almost immediately blew up over the authenticity of this object and the stone tools supposedly associated with it; and eventually, an international commission was convened to settle the matter. This committee of savants consisted of various French luminaries, plus several English scientists including George Busk. Eventually, the commission exonerated Boucher de Perthes himself as a fraudster, but remained deadlocked over the authenticity of the fossil and tools. The French intelligentsia mostly accepted them for political reasons, while the English remained opposed. And the whole affair added up to the sort of unseemly squabble that Darwin most detested and always did his best to avoid.

What’s more, there were similar and equally embarrassing scandals closer to home. In England, the so-called “Prince of Counterfeiters” was one Edward Simpson, alias “Flint Jack” (Milner 2008 ). During several years of assisting a local physician who dug for antiquities in his spare time, Flint Jack taught himself the art of stoneworking. Soon, this gifted flintknapper was producing supposedly Stone Age tools that would fool even the most expert eye. And he sold his forgeries to collectors and museums all over the country. Finally, he brazenly peddled them as his own work, before the sheer quantity of real Stone Age artifacts coming on to the market put him out of business. There can be little doubt that Darwin found all this fraud and scandal in the antiquarian marketplace very distasteful. And it must surely have been at least one more contributory factor in his reluctance to dabble in the human fossil record.

Still, it is nonetheless necessary to ask why Darwin gave even the idea of an actual fossil ancestry for humans such a wide berth in his great work on human descent. In this connection, it is quite possibly enough to conclude with Moore and Desmond ( 2004 ) that Darwin considered it simply too provocative, both politically and socially, to tie human ancestry in with any tangible evidence. For it is well known that even the contemplation of doing so caused this complex and delicate man extreme physical and mental distress; and it certainly seems plausible that Darwin felt that limiting himself to the comparative method, contrasting humans with apes, and merely conjecturing about possible transitional forms, was somehow the safest route to take. After all, those speculative intermediates remained hypothetical, unenshrined in any material object that his opponents might take exception to.

However, it is possible that another contributing factor may well have been Darwin’s rather suspicious attitude toward the fossil record itself—which in the nature of things is the only direct archive we have of the origins and evolution of the human family or any other. Of course, by its very nature, the fossil record is and always will be incomplete. And in Darwin’s time, 150 years ago, it was vastly more incomplete than it is now, and conspicuously lacked many of the intermediate forms predicted by Darwin’s theory. But while under such circumstances it is completely understandable that Darwin would not have wished to embrace the fossil record as a key element bolstering his notion, he seems to have deliberately shied away from it. Thus, under the rubric of “Objections to the Theory,” he devoted an entire chapter in the Origin of Species to the “Imperfection of the Geological Record,” enumerating reason after reason not only why this record was not adequate, but why it could not be adequate.

“Geology assuredly does not reveal any such finely graduated chain [as evolution requires]; and this, perhaps is the gravest objection which can be urged against my theory. The explanation lies, as I believe, in the extreme imperfection of the geological record.” (Darwin 1859 , p. 280).

Even in the remarkably brief chapter of the Origin in which he recruited the fossil record to his cause, Darwin was dubious:

“[numerous causes] must have tended to make the fossil record extremely imperfect, and will to a large extent explain why we do not find interminable varieties, connecting together all the extinct and existing forms of life by the finest graduated steps.” (Darwin 1859 , p. 342).

Darwin’s general wariness of the fossil record may seem a bit odd in a person who not only considered himself first and foremost a geologist, but whose nascent ideas about the history of life had been so clearly nourished by the fossils he had encountered during his voyage on the Beagle . For Darwin was always ready to acknowledge what a seminal event his discovery during the Beagle voyage of the amazing South American fossil glyptodonts had been for him. The glyptodonts are large extinct armored xenarthrans, relatives of today’s armadillos and sloths, which are found quite abundantly in Ice Age geological deposits of southern South America. And finding these extinct beasts in the very same place as surviving members of their family—something that implied the replacement of faunas by related ones—was a revelation to Darwin:

“[I was] deeply impressed by discovering in the Pampean formation great fossil animals covered with armour like that of the existing armadillos” (C. Darwin in F. Darwin 1950 , p. 52).

Indeed, as Eldredge ( 2005 ) points out, Darwin’s encounter with the glyptodonts constituted one of the three key observations that first led him toward the explicit realization that species were not immutable.

This realization was a truly formative one because, for Darwin, the adoption of the corollary belief in the “transmutation of species” was fundamental to everything that was to follow, and it was emotionally as well as intellectually a difficult transition for him to make. In an 1844 letter to Joseph Hooker, Darwin famously described how admitting his new belief was “like confessing a murder,” and it was as formidable a psychological hurdle as he faced in his entire career. Still, although his geological observations had made Darwin acutely aware of the transitory nature of everything he saw around him, he clearly felt very acutely the inadequacies of the fossil record for determining specific events. And although the notion that fossil “missing links” were out there to be discovered was soon to become a governing principle of the quest for human origins, Darwin himself seems to have remained rather dubious that such links would ever be found.

Of course, the whole notion of links, missing or otherwise, came from the medieval concept of the Great Chain of Being with which Darwin was philosophically in contention—indeed, in a marginal note in one of the Notebooks , he specifically warned himself against ever using the terms “higher” or “lower” in relation to living beings. But the Great Chain of Being, the idea that all living things were ranged in graded series, was nonetheless part of the ethos that suffused English society, and it was a notion from which Darwin found it difficult to disengage himself entirely. For it was not only a religious concept with a succession of forms leading from the most lowly pond scum, through mankind, the highest Earthly form, on up to the Angels and God above. It had political and social dimensions as well. On one hand, the Great Chain ranked the races of mankind from “lower” to “higher;” and on the other, within English society, it carried through the social order with peasants and servants at the bottom, then tradesmen and the gentry, then the nobility, and on up to royalty at the top who served to link earthly and heavenly existences. Correspondingly, the designations of “lower” and “higher,” stemming directly from the Great Chain notion, proved irresistible to zoologists: lemurs, for example, were and still are “lower” primates, while apes and humans are “higher primates.”

It is well-established that, long before he published On the Origin of Species , Darwin was fully aware that his theory firmly placed our species Homo sapiens as simply another product of the evolutionary process, among literally millions of others. So, while the effective absence of a hominid fossil record before he published the Origin may have meant that Darwin could not have made extensive reference to it there if he had wanted to, we still need to ask if there are reasons beyond the admittedly powerful sociopolitical ones why he more or less ignored it in the post-Neanderthal times of The Descent of Man . One reason for such neglect is, of course, the very specific monogenist agenda that Darwin was pursuing in that work. But another reason may be that his colleague Thomas Henry Huxley, who is often, if misleadingly, referred to as “Darwin’s Bulldog,” had already tackled the matter head-on in his 1863 book of essays, Evidence as to Man’s Place in Nature .

The last chapter in Huxley’s book was explicitly titled On Some Fossil Remains of Man , and it dealt exclusively with the best-preserved and best-documented fossil humans known at the time: the Neanderthal skullcap already mentioned, and two partial crania from Engis, in Belgium, that had been published by Philippe-Charles Schmerling in the early 1830s. By the time Huxley wrote, the Engis fossils had been certified as contemporaneous with the extinct Ice Age wooly mammoth and wooly rhinoceros by no less an authority than Darwin’s close colleague the geologist Charles Lyell, who had also pronounced the Neanderthaler to be of “great but uncertain antiquity.” We now know that one of the Engis crania, a juvenile braincase, had belonged to a Neanderthal. However, since many of the osteological differences between Homo neanderthalensis and Homo sapiens only emerge later in development, it is fully understandable that Huxley (like everyone else at the time) did not recognize it as such. And in any event, Huxley basically ignored it. The other Engis cranium was adult, and it was on a plaster cast of this specimen that Huxley based his analysis. The Engis adult clearly is a Homo sapiens and it is now known to represent a later burial into the Neanderthal deposits at the site—which means it is younger than those deposits.

Huxley’s ignorance of this fact may not in fact have mattered much, in light of his rather perfunctory and dismissive analysis of the adult Engis specimen. He recognized this cranium as that of a fully modern person, concluding that it:

“has belonged to a person of limited intellectual faculties, and we conclude thence that it belonged to a man of a low degree of civilization” (Huxley 1863 , pp. 114–115).

He then continued to the Neanderthal skull, an altogether more interesting specimen, and to which he devoted much greater space. Initially, he quoted extensively from Schaaffhausen who had declared that the bones:

“exceed all the rest in those peculiarities of conformation which lead to the conclusion of their belonging to a barbarous and savage race.” (Schaaffhausen 1861 , translated by Busk).

Huxley finally proceeded to a detailed examination of the Neanderthal skullcap, again based on a plaster cast. He was amazed by the differences between the cranial contours of the Neanderthal and Engis crania, but he noted that:

“…the posterior cerebral lobes [of the Neanderthaler] must have projected considerably beyond the cerebellum, and… [this] constitutes one among several points of similarity between [it] and certain Australian skulls” (Huxley 1863 , p. 134).

As Schwartz ( 2006 ) has pointed out, the comparison with “certain Australian skulls” comes straight out of the Great Chain of Being. For in nineteenth-century European scientific mythology, the Australian aborigines belonged, along with the South African Bushmen, to the “lowest” of races. Having established this philosophical baseline, Huxley proceeded to a long dissertation about variation in human skulls, eventually concluding that the key to comparison among them was provided by the basicranial axis, a line between certain points on the internal base of the skull:

“I have arrived at the conviction that no comparison of crania is worth very much, that is not founded upon the establishment of a relatively fixed base line… the basicranial axis.” (Huxley 1863 , pp. 138–40).

He then showed, to his own satisfaction, that relative to this axis, the basicranium became shorter “in ascending from the lower animals up to man” and that this trend was continued up from the “lower” human races to the “higher” ones. In which case:

“Now comes the important question, can we discern, between the lowest and highest forms of the human cranium, anything answering, in however slight a degree, to this revolution of the side and roof bones of the skull upon the basicranial axis observed upon so great a scale in the mammalian series? Numerous observations lead me to believe that we must answer this question in the affirmative.” (Huxley 1863 , pp 140–142).

One might object at this point that the basicranial axis had no relevance whatever to the Feldhofer Neanderthal, a specimen that totally lacked a skull base. The important thing here, though, was that Huxley had managed to establish a graded series. And by superimposing the profile of the Neanderthaler onto an Australian skull, he contrived to convince himself that:

“A small additional amount of flattening, and lengthening, with a corresponding increase of the supraciliary ridge, would convert the Australian brain case into a form identical with the aberrant [Neanderthal] fossil.” (Huxley 1863 , p. 146).

Nonetheless, whereas:

“[The Engis skull] is… a fair average human skull, which might have belonged to a philosopher, or might have contained the thoughtless brains of a savage… The case of the Neanderthal skull is very different. Under whatever aspect… we meet with ape-like characters, stamping it as the most pithecoid of human crania yet discovered” (Huxley 1863 , p. 147).

Yet, at the same time, the Neanderthal skullcap had held a large brain—larger, indeed, than the modern average. Furthermore, although the preserved bones of the individual’s skeleton were robustly built, Huxley felt that such stoutness was to be “expected in savages” (Huxley 1863 , p. 148). As a result, he concluded that:

“In no sense… can the Neanderthal bones be regarded as the remains of a human being intermediate between men and apes. At most, they demonstrate the existence of a man… somewhat toward the pithecoid type… the Neanderthal cranium… forms… the extreme term of a series leading gradually from it to the highest and best developed of human crania” (Huxley 1863 , p. 149).

By this intellectual sleight of hand, Huxley dismissed the Neanderthal find as a mere savage Homo sapiens , essentially robbing the slender human fossil record then known of any potential human precursor. Instead, in a move that was as radical in its own way as the alternative would have been, Huxley pushed the antiquity of the species Homo sapiens back into the remotest past and was moved to ask:

“Where, then, must we look for primaeval Man? Was the oldest Homo sapiens pliocene or miocene, or yet more ancient? In still older strata do the fossilized bones of an ape more anthropoid, or a Man more pithecoid, than any yet known await the researches of some unborn palaeontologist?” (Huxley 1863 , p. 150).

Taken overall, this rather startling conclusion was not just a major shift away from the demonstrable morphology of the Neanderthal specimen—which in the same year had been branded a distinct species, Homo neanderthalensis , by the Dublin anatomist William King. It was also a considerable reversal of perspective for one who had been a convinced saltationist. After all, when reviewing On the Origin of Species , Huxley had been moved to observe that:

“Mr Darwin’s position might, we think, have been even stronger than it is if he had not embarrassed himself with the aphorism ‘ natura non facit saltum ,’ which turns up so often in his pages. We believe… that Nature does make jumps now and again, and a recognition of that fact is of no small importance in disposing of many minor objections to the doctrine of transmutation” (Huxley 1860 , p. 77).

Famously combative though Huxley was, with none of Darwin’s reluctance to hash out in public the implications of evolution for human origins, he too had thus caved when it came to the contemplation of the human fossil record.

What Huxley’s motives may have been in this, it is hard to judge. But I am pretty sure that Jeffrey Schwartz ( 2006 ) was correct to suggest that, if Huxley had been writing in Man’s Place in Nature about any other mammal than a hominid, he would have reached a very different conclusion. Almost certainly, he would have discerned one of Nature’s jumps between the Neanderthaler and the avowedly “higher” type from Engis. As it was, however, Huxley elected to reject the idea that the Feldhofer Neanderthal specimen had belonged to “a human being intermediate between men and apes” in favor of viewing it as a member of Homo sapiens , via an extension into the past of the widely assumed “racial hierarchy” that expressed itself in terms not only of morphology, but of technology, society, and presumed intelligence. In a very real sense, then, it is to Huxley that we can trace the exceptionalism that has dogged paleoanthropology ever since.

Historically, however, the significance of Huxley’s contribution goes beyond this. For by employing anti-Darwinian reasoning in support of the conclusion that the Feldhofer fossil was merely a brutish Homo sapiens , Huxley had provided Darwin with just the excuse he needed not to broach the fossil evidence seriously in The Descent of Man . Darwin could brush the crucial Neanderthal fossil off in passing because Huxley, in however non-Darwinian a spirit and however much in contradiction of his own principles, had given him license to.

There were, then, many reasons why Darwin should have been disposed in The Descent of Man to shrink from any substantive discussion of whether extinct human relatives might actually be represented in fossil form. The fossil and antiquarian records were awash with fakes; any discussion of human ancestry was rife with social and political pitfalls; and anyway, by his own close colleague’s testimony, the record contained nothing that could have any relevance to ancient and now-extinct human precursors. Add to that Darwin’s innate suspicion of the distorting effects of incompleteness in the fossil record, and he may have felt that a large degree of discretion on the matter was mandatory.

None of this means, of course, that The Descent of Man has not exerted an immense influence on the sciences of human origins over the last century and a half. Just as it is easy for English speakers to forget how much they owe to William Shakespeare for the language they use daily, we tend to lose sight of the fact that much received wisdom in paleoanthropology has come down to us direct from Darwin. Darwin it was who proposed a mechanism for the structural continuity of human beings with the rest of the living world and who gave a detailed argument for human descent from an “ape-like progenitor” (1871, i, p. 59). It was Darwin who documented beyond doubt, in The Descent of Man , that all living humans belong to a unitary species with a single origin—which we now know, on the basis of evidence of which Darwin could never have dreamed, to have been around 200,000 years ago.

He also had the inspired hunch that our species originated in the continent of Africa—and again, this guess has been amply substantiated by later science. Darwin’s perceptions on the behaviors of other primates and how they relate to the way humans behave were remarkably astute, particularly given the highly anecdotal nature of what was then known.

And, for better or for worse, a single comment in The Origin is proclaimed as founding Scripture by practitioners of today’s evolutionary psychology industry:

“In the distant future I see open fields for far more important researches. Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation. Light will be thrown on the origin of man and his history” (Darwin, 1859 , p. 488; emphasis added).

Virtually every section in the first part of the Descent of Man foreshadows an area of anthropology or biology that has independently flowered since; and in this way, Darwin wrote much of the agenda that was to be followed by paleoanthropology and primatology over the next century and a half.

I just wish I knew what he really thought about the Neanderthal fossil!

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I would like to thank Niles Eldredge for inviting me to contribute this piece and Richard Milner for the valuable discussion.

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Tattersall, I. Charles Darwin and Human Evolution. Evo Edu Outreach 2 , 28–34 (2009). https://doi.org/10.1007/s12052-008-0098-8

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Charles Darwin's theory of evolution: A review of our present understanding

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The paper characterizes Darwin's theory, providing a synthesis of recent historical investigations in this area. Darwin's reading of Malthus led him to appreciate the importance of population pressures, and subsequently of natural selection, with the help of the “wedge” metaphor. But, in itself, natural selection did not furnish an adequate account of the origin of species, for which a principle of divergence was needed. Initially, Darwin attributed this to geographical isolation, but later, following his work on barnacles which underscored the significance of variation, and arising from his work on “botanical arithmetic,” he supposed that diversity allowed more “places” to be occupied in a given region. So isolation was not regarded as essential. Large regions with intense competition, and with ample variation spread by blending, would facilitate speciation. The notion of “place” was different from “niche,” and it is questioned whether Darwin's views on ecology were as modern as is commonly supposed. Two notions of “struggle” are found in Darwin's theory; and three notions of “variation.” Criticisms of his theory led him to emphasize the importance of “variation” over a range of forms. Hence the theory was “populational” rather than “typological.” The theory required a “Lamarckian” notion of inheritable changes initiated by the environment as a source of variation. Also, Darwin deployed a “use/habit” theory; and the notion of sexual selection. Selection normally acted at the level of the individual, though “kin selection” was possible. “Group selection” was hinted at for man. Darwin's thinking (and also the exposition of his theory) was generally guided by the domestic-organism analogy, which satisfied his methodological requirement of a vera causa principle.

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Wynne-Edwards, V. C.: 1962, Animal Dispersion in Relation to Social Behaviour , Oliver & Boyd, Edinburgh and London.

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Oldroyd, D.R. Charles Darwin's theory of evolution: A review of our present understanding. Biol Philos 1 , 133–168 (1986). https://doi.org/10.1007/BF00142899

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Darwin and His Theory of Evolution

At first glance, Charles Darwin seems an unlikely revolutionary. Growing up a shy and unassuming member of a wealthy British family, he appeared, at least to his father, to be idle and directionless. But even as a child, Darwin expressed an interest in nature. Later, while studying botany at Cambridge University, he was offered a chance to work as an unpaid naturalist on the HMS Beagle , a naval vessel embarking on an exploratory voyage around the world. In the course of nearly five years at sea – during which time the Beagle surveyed the coast of South America and stopped in such places as Australia and, most famously, the Galapagos Islands – Darwin took advantage of countless opportunities to observe plant and animal life and to collect both living and fossilized specimens for later study.

After the Beagle returned to England in October 1836, Darwin began reflecting on his observations and experiences, and over the next two years developed the basic outline of his groundbreaking theory of evolution through natural selection. But beyond sharing his ideas with a close circle of scientist friends, Darwin told no one of his views on the origin and development of life. Indeed, he did not publish his now-famous volume, On the Origin of Species by Means of Natural Selection , until 1859, more than 20 years after he had first formulated his theory.

On the Origin of Species may never have been written, let alone published, if it had not been for Alfred Russel Wallace, another British naturalist who independently proposed a strikingly similar theory in 1858. Wallace’s announcement prompted Darwin to publicly reveal that his own research had led him to the same conclusion decades earlier. This being the age of Victorian gentlemen, it was agreed that the two scientists would jointly publish their writings on the subject. Their work – comprising a collection of Darwin’s earlier notes and an essay by Wallace – was read to the Linnean Society, an association of naturalists, in London on July 1, 1858. The following year, Darwin published On the Origin of Species , a lengthy, fleshed-out treatment of his ideas on evolutionary theory. The book was an immediate bestseller and quickly set off a firestorm of controversy.

Darwin had expected no less – fear of a backlash from Britain’s religious and even scientific establishment had been the primary reason he had delayed publicizing his ideas. Yet the concept of species adaptation was not so radical at the time. Scientists had been debating whether animals evolved decades before Darwin put forth his theory. The idea of “transmutation of species” had been rejected by many prominent naturalists, among them French scientist Georges Cuvier, who believed that species had been created much as they appeared in his day. But transmutation also had early champions, including Darwin’s grandfather, the famed Birmingham physician Erasmus Darwin.

The younger Darwin’s achievement was to offer a plausible and compelling explanation for how species evolve and to use this explanation to trace the history of life’s development. All existing creatures, he argued, descended from a small number of original or progenitor species. Darwin compared the history of life to a great tree, its trunk representing these few common ancestors and an extensive system of branches and twigs symbolizing the great variety of life that has evolved from them.

This evolution, Darwin wrote, is due to two factors. The first factor, Darwin argued, is that each individual animal is marked by subtle differences that distinguish it from its parents. Darwin, who called these differences “variations,” understood their effect but not their cause; the idea of genetic mutation, and indeed the scientific study of genetics, would not arise fully until the early 20th century. The second factor, Darwin argued, is that although variations are random, some of them convey distinct advantages – superior camouflage, a heartier constitution or greater speed, for example – that better equip a creature to survive in its environment. A greater chance of survival allows for more opportunity to breed and pass on advantageous traits to a greater number of offspring. Over time, an advantage spreads throughout a species; in turn, the species is more likely to endure and reproduce. Thus, over the course of many generations, subtle changes occur and accumulate, eventually morphing into bigger changes and, possibly, even a new species.

While Darwin’s ideas initially challenged long-held scientific and religious belief systems, opposition to much of Darwin’s thinking among the scientific communities of the English-speaking world largely collapsed in the decades following the publication of On the Origin of Species . Yet evolution continued to be vigorously rejected by British and American churches because, religious leaders argued, the theory directly contradicted many of the core teachings of the Christian faith.

Darwin’s notion that existing species, including man, had developed over time due to constant and random change seemed to be in clear opposition to the idea that all creatures had been created “according to their kind” by God, as described in the first chapter of the biblical book of Genesis. Before Darwin, the prevailing scientific theory of life’s origins and development had held that species were fixed and that they never changed. This theory, known as “special creationism,” comported well with the biblical account of God creating the fish, fowl and mammals without mention of subsequent alteration.

Darwinian thinking also appeared to contradict the notion, central to Christianity and many other faiths, that man had a special, God-given place in the natural order. Instead, proponents of evolution pointed to signs in human anatomy – remnants of a tailbone, for instance – showing common ancestry with other mammals.

Finally, the idea of a benevolent God who cared for his creation was seemingly challenged by Darwin’s depiction of the natural world as a savage and cruel place – “red in tooth and claw,” as Darwin’s contemporary, Alfred Lord Tennyson, wrote just a few years before On the Origin of Species was published. Darwin’s theory challenged the idea that the natural world existed in benevolent harmony.

Darwin fully understood, and at times agonized over, the threat that his work might pose to traditional religious belief, explaining in an 1860 letter to American botanist Asa Gray that he “had no intention to write atheistically.” But, he went on, “I cannot see as plainly as others do … evidence of design and beneficence on all sides of us. There seems to be too much misery in the world.”

Regardless of his intentions, Darwin’s ideas provoked a harsh and immediate response from religious leaders in Britain. For instance, England’s highest-ranking Catholic official, Henry Cardinal Manning, denounced Darwin’s views as “a brutal philosophy – to wit, there is no God, and the ape is our Adam.” Samuel Wilberforce, the Anglican Archbishop of Oxford and one of the most highly respected religious leaders in 19th-century England, also condemned natural selection in a now-famous speech on what he deemed the theory’s scientific deficiencies at an 1860 meeting of the British Association for the Advancement of Science. At one point during the meeting, Wilberforce reportedly asked biologist Thomas Henry Huxley whether he was related to an ape on his grandmother’s or grandfather’s side. Huxley, whose vigorous defense of evolutionary theory would earn him the nickname “Darwin’s bulldog,” allegedly replied that he would rather be the ancestor of a monkey than an advanced and intelligent human being who employed his “knowledge and eloquence in misrepresenting those who are wearing out their lives in the search for truth.”

Some scholars now contend that Huxley’s rebuke of Wilberforce never occurred. Regardless, it was around this time that the British scientific establishment gained the upper hand in the debate over evolution. And while the public disagreement between ecclesiastical and scientific authorities did not end in the 1860s, religious thinkers became more wary of directly challenging evolution on scientific grounds. In the late 19th and early 20th centuries, churches instead focused much of their energy on resisting the idea that man had evolved from lower animal orders and hence had no special place in creation or, for that matter, a soul. Indeed, while some churches, including the Catholic Church, eventually accepted evolution as a God-directed mechanism of biological development, none questioned the role of God as the sole creator of man.

By the time of his death, in 1882, Darwin was considered the greatest scientist of his age. Moreover, the very church his theory had challenged accorded him a full state funeral and burial in Westminster Abbey, near the grave of Sir Isaac Newton. Darwin’s idea was still provocative, but by the time of his death it had gained general acceptance in Britain, even among many in the Anglican clergy. Indeed, his interment in the abbey was seen by some contemporaries as symbolic of an uneasy truce between science and religion in Britain.

This report was written by David Masci, a senior researcher at the Pew Research Center’s Religion & Public Life Project.

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Cambridge Digital Library

Darwin manuscripts.

One may say there is a force like a hundred thousand wedges trying force ‹into› every kind of adapted structure into the gaps ‹of› in the œconomy of Nature, or rather forming gaps by thrusting out weaker ones Charles Darwin Notebook D 135e, 28 September 1838

The Charles Darwin Papers in the Manuscripts Department of Cambridge University Library hold nearly the entire extant collection of Darwin’s working scientific papers. Paramount among these documents are Charles Darwin’s Evolution Manuscripts , which are being published online at the Cambridge Digital Library and simultaneously at the Darwin Manuscripts Project in collaboration with the Darwin Correspondence Project . This is a conceptually coherent set of over 30,000 digitised and edited manuscript pages, spanning 1835-1882. None of these documents have hitherto been digitised to the present high standard of full-colour and high-resolution. While several documents are classics of the Darwin manuscripts corpus, many have never been transcribed and edited before and many that have been published previously are presented here in new and radically improved editions. These documents are organised into two parts, which will be released in two instalments: Creation of the Origin (November 2014) and Darwin’s Evidence (June 2015).

Part I Creation of the Origin of Species includes the first traces of Darwin’s interest during the Beagle voyage in the species question—broadly defined. It also includes, for contextual purposes, his treatment of those specimens in his own collections and those subjects, such as extinction and biogeography, which he would later revisit in the light of evolution. Beyond these scattered, early theoretical reflections, the bulk of the Creation collection comprises the complete set of theoretical notes and the multiple draft essays that Darwin wrote over a period of two decades (1837-1859). These documents truly constitute the surviving seedbed of the Origin . For in them, Darwin hammered out natural selection and the structure of concepts he used to support natural selection. It was here also that he developed his evolutionary narrative and where he experimented privately with arguments and strategies of presentation that he either rejected or that eventually saw the light of day with the Origin ’s publication in 1859.

In the collection, there are several repositories of notes namely: the Transmutation Notebooks and Metaphysical Notebooks of the 1830s. It was in Notebook B, the first Transmutation Notebook, that Darwin first attempted to formulate a full theory of evolution and it was in Notebooks D and E that natural selection began to take form in late 1838 and early 1839. The further maturation of Darwin’s theory is found in the three experiment notebooks he began in the late 1830s and mid 1850s, and above all in the Origin Portfolios. The latter are a large mass of previously unpublished loose notes, primarily from the 1830s-1850s, which Darwin organised into topics that generally parallel the chapters of the Origin . The Origin Portfolios contain several hundred letters and former enclosures in letters, which Darwin commonly annotated and which he treated as an integral part of the material he gathered for what became the Origin .

Lastly, the Creation collection holds the surviving documentary evidence for the drafting of the Origin , which was a process that scholars have long recognised began not in the 1850s, but in 1842 when Darwin wrote the first in a long chain of draft essays and draft chapters. The first of these was the 35-page document known as the 1842 Pencil Sketch or the 1842 Essay . Darwin was right to refer to the 1842 document as a ‘sketch’ for it was very rough. But this often crudely schematic document does represent a very first draft of the Origin . Darwin managed to cover much of the over-arching structure, many of the themes, and even some of the most memorable language of the book that he was to publish much expanded, many drafts and many years later. For example, it was in this sketch that Darwin for the first time coined the term Natural Selection, where it appeared as the section head for the two crucial pages of the 1842 Essay that he devoted to the explanatory essence of his theory ( Ms pp. 5 & 6 ). Darwin began page 5, but quickly crossed-through the short passage he had written. He turned over the page and replaced it with a new page 5. However, that new start occasioned a historic change and crystallisation of Darwin's scientific language. For, in the first p. 5 he used the circumlocution 'Means of selection', which he then extended to the fairly long phrase '<<Natural>> Means of selection'. But on the new page 5, he began a new section with a new heading, and as far as is known, it was at this moment that Darwin coined a new scientific term: 'Natural Selection'.

The 1844 Essay , a 189-page draft, was to follow next. Possibly before he launched into writing the 1844 Essay, and definitely during 1844 Essay’s writing, he used the backs of many pages of the 1842 Pencil Sketch to write ink chapter summaries and notes, some with page references to the draft of the 1844 Essay. Darwin also rewrote the opening dozen or so pages of the 1844 draft, but retained the rejected version—published here as 1844 Essay, Part I, Draft A . After he completed writing the 1844 Essay, he had it copied by an amanuensis to produce a 230 page fair copy , which he may well have intended to publish. If so, Darwin thought better of the idea, but he did revise and annotate the fair copy, which was also critically annotated—with significant impact—by Emma Darwin and Joseph Dalton Hooker, among others.

One set of Darwin’s annotations on the 1844 Essay, namely dark pencil notes on the verso of blank sheets interleaved among the pages of the fair copy, appear to relate to the next phase of Darwin’s writing up the species theory. That is the nine surviving chapters of the very large manuscript (comprising nine thick volumes of the Charles Darwin Papers, DAR 8-16) published posthumously by R. C. Stauffer in 1975 as Charles Darwin’s Natural Selection, Being the second part of his big species book written from 1856 to 1858 . While it is true—as we learn from Darwin’s pocket diary (DAR 158)—that he first took pen to foolscap to begin writing Natural Selection in May 1856, we also know from the diary that it was earlier, that is in September 1854, that Darwin actually reengaged with the writing project he had dropped in 1844. He did so not by embarking on a new version of the theory, rather he ‘began sorting notes for species Theory’. This correlates well with the establishment of the Origin Portfolios for his old notes and with a sudden influx of new notes, many datable to November 1854.

The Natural Selection manuscript is the immediate, yet partial, precursor of the Origin . Stauffer refers to it as the ‘second part of his big species book’. The first part, dealing with variation and selection under domestication, was apparently cannibalised either when Darwin wrote Chapters 1 and 2 of the Origin and/or when he wrote Variation under domestication (1868). We know from the Diary that there were two lost, presumably reused, Chapters I and II. So the Natural Selection manuscript begins with Chapter III and is complete through Chapter X, while Chapter XI is incomplete. The eight surviving full chapters comprising Natural Selection clearly show that the big book was conceived on a larger scale than the Origin . It is characterized by its richness of detail and the fact that it has footnotes and a presumptive bibliography. Darwin hoped that it would be published in 1860. In fact, when he stopped writing in June 1858, he had not that much further to do to complete the book to the draft stage. Judging by the Origin , he had but four topics left to cover. He had to complete geographic distribution, write de novo chapters on palaeontology and on the related topics he grouped together under classification, morphology, embryology, and rudimentary organs, and he had to write the concluding chapter. In other words, 70% of the topics were already done, and while distribution and palaeontology could well have become double chapters, as they are in the Origin , the remaining topics contained no conceptual difficulties to compare with those, such as divergence and instinct that he had already resolved, at least to his own satisfaction. Given the rate that Darwin was working, publication sometime in 1859-1861 was definitely in sight.

But in June 1858, as he noted in his diary, his writing was ‘interrupted’, as is well known, by the arrival of Alfred Russel Wallace’s paper espousing not only evolution, but evolution by an agency that Darwin in his shock saw—accurately or not—as closely akin to natural selection. By July Darwin had regrouped and began writing what he called an abstract of the big book. This new version of the species book would have no footnotes or bibliography, have far less detail, and would be far more readable than Natural Selection . Some nine months later, in March 1859, the abstract was completed and was published on 24 November 1859 as On the Origin of Species, or the preservation of favoured races in the struggle for life . While Darwin carefully preserved many thousands of manuscript pages leading up to the draft of the Origin , and continued to add notes to the Origin portfolios into the 1870s, he seems to have placed little value on preserving the draft itself, and all that survive seem to be mainly those few sheets whose blank sides were used by his children, particularly his son Francis, for drawing paper and those retrieved from the trash basket by others of Darwin’s children, particularly his daughter Henrietta. In total, 45 manuscript pages of the draft, 7 slips with lettered inserts to various pages and 1 fair copy page have been found. Of the 45 full sheets, 26 sheets are part of the Charles Darwin Papers in Cambridge. Most of the latter were distributed as souvenirs by Leonard Darwin acting in consort with his sister Henrietta either to other members of the family or to various scientists and scientific institutions. Leonard in particular gave sheets to fellow supporters of the eugenics movement in Britain and the United States. Ultimately many of the distributed sheets were sold on the open market to collectors and major libraries. Thus the small surviving trove of Origin sheets is the one and only element of the Creation of the Origin collection that isn’t wholly held by Cambridge University Library and Down House.

Part II Darwin’s Evidence — the second half and final instalment of Charles Darwin’s Evolution Manuscripts, will be released in June 2015 and constitutes the full, extant documentary record of notes and drafts for the extensive empirical research programme that Darwin undertook in preparing his eight post- Origin books on plants and humans. Darwin used the many experiments and observations he conducted, and the mass of information he compiled from his reading, to establish a well-worked evidentiary framework to support the central theoretical claim of the Origin , namely: that selection has worked in nature to produce evolutionary adaptations. For humans his most focussed empirical study led to Expression of Emotions , which appeared in 1872 and was a compliment to the Descent of Man (1871), which is based on a large compilation of information extracted from the scientific literature. For plants Darwin observed, dissected, and experimented on a wide variety of adaptive phenomena, namely: orchid fertilisation strategies ( Orchids 1862, 1877), complex outbreeding mechanisms such as heterostyly and dichogamy ( Cross and Self Fertilisation , 1876 and Forms of Flowers 1877), and a series of physiological books ( Insectivorous Plants , 1875) and various forms of movement, such as climbing and phototropism ( Climbing Plants , 1865, 1875 and Power of Movement 1880).

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Darwinian natural selection: its enduring explanatory power

Evolutionary theory has never had a stronger scientific foundation than it does today. In a short review I hope to portray the deep commitment of today's biologists to Darwinian natural selection and to discoveries made since Darwin's time. In spite of the scientific advances in the century and a half since the publication of On the Origin of Species , Darwin still remains the principal author of modern evolutionary theory. He is one of the greatest contributors of all time to our understanding of nature.

An awesome gulf divides the pre-Darwinian world from ours. Awesome is not too strong a word…. The theory of natural selection revolutionised our understanding of living things, furnishing us with a comprehension of our existence where previously science had stood silent. –Helena Cronin ( 1 )

The deluge continued day after day on the tiny island of Daphne Major in the Galápagos Islands, 600 miles off the coast of Ecuador. Dusty soil from years of drought washed in torrents down the steep volcanic slopes into the surrounding sea. Plants began to sprout that had lain dormant for years, and vines grew up the tent poles of the researchers on the only flat ground high up near the extinct volcano's rim. Some plants producing large seeds were smothered by the prolific vines, and others flourished. The finches on the island celebrated by “going crazy,” in the words of one researcher—the males sang, established territory, and mated. The young grew fast on the insects that appeared all over the island, and they began mating at an unusually young age. The findings from this unusual year provided stunning evidence that natural selection was working on every generation of ground finches, changing the calculus of reproductive success and the composition of alleles in the gene pool of the species.

The biologists Peter and Rosemary Grant began studying Darwin's finches in 1973, and their research has continued full-time ever since ( 2 , 3 ). It is the longest field study in biology other than that of Jane Goodall, who has studied chimpanzees in Tanzania since 1962. Younger biologists have assisted the Grants in their study, so that the ground finches of Daphne Major have been studied in great detail every year since 1973.

Daphne Major is a volcanic cone with a central crater; the island is only one half mile long (Figure ​ (Figure1 1 ) . No tourists visit the island because there is no place to land. Steep cliffs encircle almost the entire perimeter, some with reverse slopes and all with waves battering their sides. Embarkation onto the slopes involves maneuvering a small boat next to an area of relatively flat volcanic surface and jumping onto the surface as the wave hovers briefly at the right level. For researchers, this means negotiating the hair-raising landing while carrying tents, food, and research equipment.

An extinct volcanic cone forms the tiny island of Daphne Major in the Galápagos, home of one of the longest studies of natural selection acting on single generations in the wild. Reprinted with permission from Grant PR, Grant BR. How and Why Species Multiply: The Radiation of Darwin's Finches . Princeton, NJ: Princeton University Press, 2008.

This inaccessibility has made the island an ideal place for the isolated study of animals that have arrived by water or by air and have established a foothold and reproduced. Island species are free from the competition of innumerable mainland species, but are faced with the challenge of how to exploit the sparse resources of their small world.

Ground finches on the island are tame, letting researchers walk up to them at times and even landing on their arms as they are measuring the beak size of one bird with calipers. Because they don't migrate, they are available for study year round. There is no obstructing vegetation to hamper observations with binoculars. There are no tourists to disturb the fiches or the researchers. For these reasons and more, the island has been described as a natural laboratory.

In 2008 the Grants, who teach biology at Princeton, published a scientific volume about their study. Their findings would have been stunning to Charles Darwin, who believed that evolutionary changes brought about by natural selection would become evident only after long periods of time. Instead, every generation of ground finches has produced evidence of changes in morphology and allele frequencies in the population of one ground finch, Geospiza fortis . The birds and their genes were changed by the severe selection pressures of the years of harsh drought; small seeds were scarce, and those individuals with smaller beak depth and smaller body size died. Evolution placed a meaning on death . Through the death of individuals less fit in the prevailing environment, alleles coding for less useful variations became less common in the gene pool. This is nothing less than evolution occurring in real time, measurable in only months, and brought about only by natural selection—the differential survival of alleles that code for more useful traits.

The beak of finches is their secret for manipulating seeds. In his superb book about the Grants’ research, The Beak of the Finch , Jonathan Weiner reminded us ( 4 ): “Beaks are to birds what hands are to us. They are the birds’ chief tools for handling, managing, and manipulating the things of this world…. Each beak is a hand with a single permanent gesture.” Beaks are continually reshaped to maximize their efficiency in crushing seeds of specific sizes and shapes and can be compared to pliers and wrenches (Figure ​ (Figure2 2 ) .

Bird beaks are like pliers and wrenches, each adapted to its own narrow task, and are constrained in their size and shape by the demands of the ongoing environment in which the bird lives and reproduces. Reprinted with permission from Grant PR, Grant BR. How and Why Species Multiply: The Radiation of Darwin's Finches . Princeton, NJ: Princeton University Press, 2008.

Torrential rains came to the Galápagos in 1983 during the most severe El Niño event in 400 years, as documented in the coral reef fossil record. Research data from this 1 year on Daphne Major required still another year for entering it all into a computer. The final analysis was stunning: birds with large bodies and deeper beaks were dying; small birds with less deep beaks were thriving. Natural selection had reversed its direction . Now on the island small seeds were abundant, and trees producing large seeds were choked by vines. Death of the less fit became an evolutionary “force,” and the gene pool of G. fortis changed again. So did the morphology of the birds, which were now smaller in average body size, with a more pointed beak than in the 1970s. Generation by generation, natural selection could be monitored as it occurred.

These findings are robustly documented by elaborate analyses involving 1) beak and body measurements of thousands of birds on the island, 2) observations of behavior, 3) studies of embryonic development, and 4) genetic sequencing of both nuclear and mitochondrial DNA. The issue of fundamental complexity is thus addressed: morphology, behavior, and the genetic code itself changed pari passu with selection pressures. One may argue that this is only correlation, but it is such consistent and remarkable correlation that causation is the only reasonable conclusion. There is no contender for causation other than natural selection. Over the years since these early studies, findings have enabled testing through predictions, in which the correlation has remained true.

Natural selection is no more, no less, than the changing representation of alleles that code for traits selected for by the environment. It is not a “force,” although “evolutionary force” is an expression that is often used to describe it. It is just the differential survival of alleles in succeeding populations. The environment may be natural or artificial; we know that our artificial environment of antibiotics provides a selective force for alleles in microorganisms that contribute to antimicrobial resistance. There is no fundamental difference in the dynamics of natural and artificial selection. Darwin knew this and began his major opus with a long discussion of the domestication of animals and plants as an excellent analogy to natural selection in the wild.

The term “islands” refers not only to oceanic islands, but also to freshwater lakes separated from each other (in which innumerable fish species have evolved, for example, the African cichlids), and even to human bodies, in each of which HIV-1 evolves into a smorgasbord of “quasispecies” variants over the course of infection. The field of biological science that addresses geographic diversity is called biogeography . Geographic isolation enables a population to evolve without the intermixing of genes from other populations. Sometimes that proceeds to speciation, or the creation of a new species—reproductively isolated from other species. At other times it may go part of the way, with the creation of variants or subspecies.

When I recently visited the White Sands National Monument in Arizona, I learned of a striking example of natural selection on the “islands” of extremely white sand dunes, which are made of gypsum (hydrated calcium sulfate) sand crystals. The dunes are so white that they resemble a snowscape. Three small diurnal (day-active) lizards live in the dunes, having recently evolved from closely related species that live in the brown soils of the surrounding Chihuahuan Desert. The White Sands species are no longer brown but almost white, perfectly mimicking the color of the sands (Figure ​ (Figure3 3 ) . When mating, they demonstrate a preference for white color morphs if given a choice in laboratory tests. Researcher Erica B. Rosenblum of the University of California at Berkeley has found a genetic basis for this color change, stemming from mutations in the melanocortin-1 receptor gene, which has a key role in producing melanin in vertebrates ( 5 ). She explained to me that the change is caused by allelic variants conferring adaptive coloration, not by epigenetic gene silencing or by phenotypic plasticity (variable phenotypic expression without genetic change). It thus represents true genetic differentiation brought about by natural selection operating in a relatively new environment. The fast-track evolution reminded me of the Galápagos finch study; in fact, the White Sands newspaper sported the headline, “The Galápagos Islands of North America!”

The bleached earless lizard, which lives only in White Sands National Monument, New Mexico, has evolved in only 2000 to 6000 years from a darker form living in the surrounding sands of the Chihuahuan Desert. The color change, along with changes in several other traits, has been mapped to gene mutations favored by natural selection. Photograph by Greg and Mary Beth Dimijian.

Natural selection is one of the pillars of contemporary evolutionary theory. Nevertheless, there are other causes of biotic evolution, some of which were unknown to Darwin. These are addressed after a further elaboration on natural selection.

MORE ABOUT NATURAL SELECTION

Bricolage is a wonderful French word, the best English translation being “tinkering.” It was first used by François Jacob in 1977 to describe how evolution uses “whatever he [a tinkerer] finds around him whether it be pieces of string, fragments of wood, or old cardboards” to fashion new structures or behavior coded for by genes. Jacob explained: “Evolution does not produce novelties from scratch. It works on what already exists…. The appearance of new molecular structures during much of biological evolution must, therefore, have rested on alteration of preexisting ones” ( 6 ).

Biological structures are thus palimpsests , with layers upon layers of history, like an old scroll erased and written over many times. One example is the vertebral column, which has been tinkered with and modified many times in vertebrate history. In the evolutionary history of whales, there is a stunning discovery: the pelvis becomes detached from the spine, as it is no longer needed to support hind limbs. The whale's range of spinal motion is thus increased, and tiny hind limbs appear in the soft-tissue areas of fossils as relics of ancestors, destined to disappear completely in modern whales.

Other structures in animals are rendered obsolete, such as eyes in some cave-dwelling fishes. The term vestigial has been used to describe these structures; they are remnants of organs once useful to an evolutionary ancestor. Genes are no exception; innumerable examples of vestigial genes, some “rusting away” like submarines on the ocean floor, have been uncovered in animal genomes.

For bird lovers, a striking example of bricolage and co-opting of earlier structures is the avian feather. In the past decade paleontologists have found hundreds of fossils of feathered dinosaurs, some with fluffy down, some with simple barbs, still others with hollow filaments. The transition from scales to feathers may have hinged on a relatively simple genetic switch. What adaptive benefits might feathers have conferred on dinosaurs? The same that they confer on birds today: warmth, cryptic coloration, showy patterns used in courtship, and possibly gliding to the ground from low platforms. One chicken-sized dinosaur had feathers on arms, legs, and toes. Even though these feathered dinosaurs were not capable of flight, protofeathers and true feathers may have paved the way for true flight millions of years later. It's an example of “exaptation,” the assignment of a new adaptive function to a structure that evolved under different selective pressures in an earlier environment.

The evolution of vertebrate limbs from the fins of fish is yet another example of a new assignment (by natural selection) to an earlier structure. Fossil finds have recently come one after the other. Tiktaalik , a 375-million-year-old fossil found in 2004, is the colorful name given to a fish skeleton with gills, the first neck, and the first front limbs; the limbs consisted of a functional wrist, elbow, and shoulder—the owner could “do push-ups.” More recently, in 2011, came the discovery of pelvic-fin muscles in the first fishes to emerge on land ( 7 ). Here was evidence of a weight-bearing pelvis, hindlimbs, and their associated musculature—and the “rear-wheel drive” strategy that characterizes terrestrial locomotion in most vertebrates. Play the fossil frames in a movie sequence and you see the emergence of fishes onto land.

Even the abrupt Cambrian “explosion” of life 541 million years ago is yielding up its secrets. There is growing evidence from molecular sequences, molecular clocks, and developmental histories that most of the Cambrian fauna originated tens to hundreds of millions of years before the onset of the Cambrian, leaving a clear fossil signature only in the Cambrian ( 8 ). Darwin has been vindicated in his prediction that this apparent anomaly would some day be resolved with evidence of ancestral lineages leading up to the explosive appearance of fossils in the Cambrian.

Paleontologists stress that it is time to move past the simplistic question, “Where are the missing links in the fossil record of life?” Instead, it is time to accept that 1) the fossil record is now extraordinarily rich, and 2) a seamless record is an impossible goal. Any transition between fossils will always be a “missing link.”

If you think the above examples of bricolage are amazing, get ready for this one. The stapes (or stirrup, the innermost of the three middle-ear bones) originated as the hyomandibular bone in fishes, supporting the gills. It later migrated to the hard palate, which it braced against the cranium in jawed fishes and the earliest tetrapods. It made a third change to become the columella in the middle ear of birds and the stapes of the middle-ear bones in mammals. Now a hearing aid, it was once a feeding aid and even earlier a breathing aid . And there is this: When an immature opossum is born, it climbs into its mother's pouch with its future ear bones still articulating its jaws. The stapes will migrate to the middle ear as the embryo develops. There is hard anatomical evidence supporting these anatomical transitions ( 9 ). What better example is there of a “fossil record” in development?

Remember that for natural selection to act, there must be 1) genetic variation in a population, 2) occasional mutations, and 3) mixing of genetic entities, either during reproduction (as in eukaryotic sexual reproduction) or in horizontal gene flow (as in bacteria and viruses).

Crypsis (hiddenness) is a relatively simple case of natural selection. It refers to camouflaged body color or shape, and to behavior that enhances concealment. We have discussed crypsis in lizards in the White Sands National Monument. Behavioral crypsis is obvious in the immobility and squinted eyes of the Scops Owl on the bare tree branch in the Okavango Delta of Botswana (Figure ​ (Figure4 4 ) . It is useful for hiding from predators (if you are potential prey) or for remaining unseen by potential prey (if you are a predator). The role of natural selection is inferential, but no other explanation comes close. Alleles arising by chance mutations, which cause crypsis, render an animal less visible to predators or prey. Such alleles are more successful than competitor alleles in getting into the next generation, by virtue of the benefits they confer. The mutations may be random, but natural selection is anything but random.

Only 8 inches tall, the Scops Owl is almost invisible on the bare branch that is its home, in the Okavango Delta of Botswana. Its extraordinary camouflage includes anatomy and behavior: its breast feathers resemble tree bark, and it remains immobile during the day, keeping its eyes closed so that it is less likely to be spotted by Africa's diurnal birds of prey. Photograph by Greg and Mary Beth Dimijian.

Mimicry is another relatively simple example of natural selection. If one animal is toxic to predators, and predators learn to avoid it, another animal will benefit from mimicking the same disguise. A hawkmoth caterpillar in a Costa Rican cloud forest displays conspicuous eyespots (its real eyes are tiny) and a soft, fake stinger (Figure ​ (Figure5 5 ) .

Munching on a plant stem in Costa Rica's Monteverde Cloud Forest Reserve, this Xylophanes caterpillar exhibits fake eyes and stinger. Its real eyes are so tiny that you would need a hand lens to see them. Photograph by Greg and Mary Beth Dimijian.

Do plants ever “lie”? Consider the passionfruit vine, often parasitized by butterfly eggs that hatch into caterpillars. The caterpillars feed on the leaves. If mutations occur in the plant that produce light-colored spots on the leaves (Figure ​ (Figure6 6 ) , they might just resemble eggs laid by Heliconius butterflies. Experiments have shown that these butterflies are less likely to lay eggs on host plants that have eggs or egglike plant structures ( 10 ). Again, natural selection is the only candidate explanation.

Do plants tell lies? Passionflower vine leaves in Costa Rica do, preserving mutations that produce spots closely mimicking eggs of Heliconius butterflies. Plants with the spots are protected from caterpillar predation because butterflies choose to lay their eggs on other plants. Photograph by Greg and Mary Beth Dimijian.

What about bacteria and viruses? Even though they don't reproduce sexually, they both enjoy high levels of horizontal gene transfer (“parasexual reproduction”) and maintain populations with high genetic diversity. There is thus ample variation for selection to act on. Under an antibiotic regime, selection occurs exactly as in Darwin's finches on the Galápagos. Differential death is the great reaper, eliminating the less fit.

Antibiotic resistance occurs not only in modern medicine but also in nature, where microbes, plants, fungi, and insects make their own antimicrobials. It is no surprise to find that these natural antimicrobials must keep evolving in the universal host-pathogen arms race. A study in 2011 demonstrated antibiotic resistance genes comprising part of fossil bacterial DNA 30,000 years old. Those same genes are found today in modern bacteria, where they encode resistance to beta-lactam, tetracycline, and glycopeptide antibiotics ( 11 ).

Just think: before Darwin, essentialism was the prevalent view of nature. Each species had an “essence” that was as unchanging as chemical elements in the periodic table. Each plant and animal species was believed to have originated in the same form as we see it today.

DOMESTICATION OF ANIMALS

Domestication is not just an excellent analogy of natural selection. It's also a good experiment. –Richard Dawkins ( 12 )

The best experiment ever made in animal domestication ( 13 , 14 ) is the ongoing study of silver foxes, initiated in the 1950s by the Russian geneticist Dmitry K. Belyaev (Figure ​ (Figure7 7 ) . On a Siberian fur farm, Belyaev raised silver foxes, Vulpes vulpes , and observed the young of each litter. Without prompting, he and his coworkers noted which juveniles were friendly and which avoided human contact. The friendly “tame” ones were later mated with tame members of other litters, and this mating selection was performed generation after generation. Only tameness was selected for. Now, over 50 years later, the result is a breed of foxes never imagined before: friendly from birth, begging for attention, and with striking anatomical changes: a piebald coat color (with a white patch on the top of the head, seen in border collies, pigs, horses, and cows), short legs, a curled-up tail, and floppy ears. Charles Darwin, who loved dogs and spent much of his life studying domestication, would have been stunned. These changes, which occurred over only 40 generations, reflect changed timing of developmental processes . Childlike traits prolonged into adulthood are an example of neoteny —neo-, “new,” and -teny, “holding onto.” Belyaev's unique experiment compressed into decades an ancient process that unfolded over centuries. Instead of foxes, wolves are believed to be the ancestral canids that were domesticated into the hundreds of dog breeds that have become our “best friends” (Figure ​ (Figure8 8 ) .

A silver fox pup shows tame and affectionate behavior, which results from selective breeding in the longest scientific study of domestication ever made, conceived by the Russian geneticist Dmitry K. Belyaev in the 1950s. Reprinted with permission from Trut LN. Early canid domestication: the farm-fox experiment. American Scientist 1999;87( 2 ):160–169.

Over the past 10,000 to 15,000 years, humans have domesticated the Eurasian wolf and used its natural genetic variation to create hundreds of breeds of domestic dogs. Reprinted with permission from Ellegren H. Genomics: the dog has its day. Nature 2005;438(7069):745–746.

Dog fossils have been found at archeological sites dating from 11,500 to 15,500 years ago ( 15 ). It is not surprising that dogs were domesticated long ago. They have served humans as close companions, guard dogs, police dogs, herding dogs, hunting dogs, sled dogs, military dogs, seeing dogs for the blind, and olfactory search dogs. Have dogs domesticated us as well? They may have secured equally important services from us, from feeding to family membership. There is, however, at least one example of a serious disservice we are guilty of: the bulldog's craniofacial malformation, in which facial shortening has created severe medical problems (Figure ​ (Figure9 9 ) . In the bulldog's unfortunate outcome, domestication differs from natural selection. Such a defective phenotype would quickly be eliminated from the reproductive pool by natural selection.

The bulldog skull before 1890 (top) and its unfortunate fate through selective breeding in 1935 (bottom). Craniofacial malformation has created serious medical problems, which we would attempt to correct if they occurred in humans. Reprinted with permission from Thomson KS. The fall and rise of the English Bulldog. Amer Scientist 1996;84:220–223.

Are we domesticating ourselves ? Consider the following features of modern life:

• Sanitary sewerage disposal
• Clean water
• Refrigeration
• Climate control
• Modern medical care
• “Assisted reproduction”—in vitro fertilization, preimplantation genetic diagnosis, intracytoplasmic sperm injection

A more troubling question is: Are we eliminating alleles for “robust” traits from the human gene pool?

ENDOGENOUS VIRAL ELEMENTS

Viruses, especially bacteriophages (“phages,” viruses that infect bacteria), may be the most numerous and ubiquitous genetic entities on the planet. Genetic sampling techniques show that seawater is a soup of viruses. Bacterial turnover on Earth occurs daily through the most common predator-prey relation known, that of phages and bacteria. Whether or not you choose to consider viruses as living entities, they are visible to natural selection, just as cellular genetic entities are.

There is an “archeological record” of past infections by viruses that inserted their genes seamlessly into our DNA ( 16 ). These genes are recognized by their sequence similarity to present-day viruses. Many have been found to be degraded, some more than others. Endogenous viral elements (EVEs) constitute a significant portion of our genome—as much as 8%. That's over 6 times more DNA than is found in all of our 20,000 protein-coding genes. They are replicated in Mendelian fashion every time a cell divides.

Most EVEs are retroviruses (which, like HIV-1, convert their RNA to DNA and insert it directly into our genome), but some are nonretroviral, such as Ebola-like and herpesvirus-like sequences. Retroviral EVEs are called ERVs (endogenous retroviruses) and HERVs (human endogenous retroviruses). The age of endogenous viruses can be estimated by molecular clock techniques, because they are confined to a host genome and therefore “frozen” in a slower mutational state than freely existing viruses.

EVEs constitute direct evidence that modern viral lineages have very ancient roots. Lentiviruses are 2 to 4 million years old; filoviruses, 12 to 30 million years. The science writer Matt Ridley has said: “If you think being descended from apes is bad for your self-esteem, then get used to the idea that you are also descended from viruses” ( 17 ).

PALEOANTHROPOLOGY

During only the past decade, fossil discoveries in Africa, Asia, and the Near East have provided an extraordinary sequence of the transition from arboreal to terrestrial locomotion in early hominins. One of the defining characteristics of hominins is bipedalism, and we are fast approaching an almost seamless fossil record of skeletal adaptations progressing through intermediate stages to fully bipedal, with the requisite changes in foot, ankle, knee, pelvis, vertebral column, upper extremities, and forward placement of the foramen magnum. These changes occurred as forests in East Africa were changing into a more open habitat, typical of the “wooded grasslands” of the East African savannah today. Bipedal locomotion enabled a huge increase in efficiency for traveling long distances in search of food and a new habitat, especially when carrying children.

The most stunning finding of paleoanthropology, however, has been this: in only 3 million years the hominin body size doubled and the brain tripled in volume to its present size, violating the usual “rules” of allometry. Typically in mammals, if body weight doubles (× 2 1 ), brain weight increases not by 2 1 but by about 2 3/4 or about 1.7 times. Instead, our intracranial volume increased 3 times, with the neocortex expanding the most. More sophisticated tools, long-distance trade, language, and the earliest art accompanied the encephalization. There can be no better evidence of natural and sexual selection, even though the evidence is “only” inferential and cannot be verified experimentally. Once the stage was set—with hands free to manipulate objects, brain structures capable of complex language, and an omnivore's gastrointestinal tract providing more efficient energy extraction from a diet of plants and animals—brain expansion progressed steadily and inexorably. Cooperation among kin and tribal members may have contributed significantly to survival of children, who—with their early birth and large brain—required a long period of upbringing.

PROCESSES OTHER THAN NATURAL SELECTION THAT CONTRIBUTE TO EVOLUTION, SOME UNKNOWN TO DARWIN

Natural selection is not the only process by which life evolves. I have listed other processes and mechanisms below in a short outline.

• Sexual selection . Proposed by Darwin and rejected by Alfred Russel Wallace, sexual selection is distinct from natural selection and involves mate choice (intersexual selection) and competition between members of the same sex (intrasexual selection). Even though sexual selection is “natural,” it is not the same as natural selection and may even oppose natural selection, as in the case of male ornaments and bright colors that make the male more vulnerable to predation.
• Endosymbiosis . “Endo,” or inside , and “symbiosis,” or living together , refer to the incorporation of a microscopic organism such as a bacterium into a larger cell, such as the protoeukaryotic cell. Mitochondria and chloroplasts have all the identifying traits of bacteria, and they perform crucial functions today (ATP synthesis and photosynthesis, respectively). Most of their genes have migrated to the host cell nucleus and are integrated into the nuclear genome, seamlessly joined in a now obligate partnership—one of the most critical events in the history of the eukaryotic cell. Endosymbiosis is an example of inheritance of acquired characteristics , i.e., Lamarckism. Surprisingly, it is entirely compatible with Darwinian natural selection acting on each partner independently; as with other mutualisms, it confers benefits upon both partners.
• Major extinctions . Both fit and unfit have perished together in Earth's great mass extinctions, the latest of which—the “Anthropocene” (also dubbed the “Homogenocene”)—has been proposed as being underway. (Who would doubt this?)
• Genetic drift in small populations . Without the buffering effect of large population size, accidents eliminate fit and unfit alike, and gene frequencies would thus change in the population, some at random.
• “Accelerated evolution.” An increased mutation rate appears to have occurred in some gene regions of humans—one in neurons playing a key role in the developing cerebral cortex, and another in the FOXP2 gene, involved in human speech. This accelerated mutation rate seems also to occur in some bacterial populations subjected to stress. Something is “tampering” with mutations, providing a surplus when they are needed for a diversity of lottery tickets. The mechanism of this acceleration is unknown, but it sounds as if it may be adaptive—and thus visible to natural selection.
• Neutral protein polymorphisms . Different structural forms of a protein that have little or no effect on the phenotype are invisible to natural selection in some environments.
• Epigenetics and gene regulation . See discussion immediately below.

EPIGENETICS

At the interface of gene and environment, epigenetics (epigenomics) addresses heritable changes in gene expression that cannot be explained by changes in DNA sequence. In eukaryotes and prokaryotes, epigenetic changes can activate, reduce, or completely disable a gene's activity. Epigenetic “marks” control access to DNA by different mechanisms, one of which is methylation of cytosine. Small noncoding RNAs (“noncoding” meaning not coding for proteins) are believed to be another agent of epigenetic change. The terms “epigenetic” and “epigenome” are still somewhat fluid and subject to change.

Early in the embryonic development of multicellular organisms, undifferentiated stem cells develop into the many different cells of the developing organism, through the silencing of genes. These changes, also called “epigenetic,” usually last for a lifetime, so that a liver remains a liver. A cancer cell, however, may undergo epigenetic reprogramming, and “epimutations” may contribute to aging.

Some epigenetic marks change as the organism responds to environmental change, such as starvation, stress, or disease, and some of these marks may persist for several generations (and are thus called “transgenerational epigenetic inheritance”). Mapping the epigenome has become increasingly important as we realize that the genome holds only a fraction of the information needed to understand development and disease.

Genome-wide association studies are uncovering evidence of polygenic (many-genes) predisposition to specific diseases ( 20 ). Many of these genetic predispositions involve noncoding DNA that regulates gene expression. Many so-called “genetic” diseases may have their origin in such epigenetic changes.

Does epigenetics change our understanding of evolution? Two studies in 2011, one in the plant Arabidopsis thaliana ( 18 ) and the other in the nematode Caenorhabditis elegans ( 19 ), showed epimutations that changed the phenotype for only a few generations. The changes, though inherited, were unstable over short time periods. Such cycling is not characteristic of genomic DNA, which remains relatively stable over time.

Epigenetically silenced alleles seem to be taken out of the selection pool for short periods of time. This could affect evolution by natural selection on short time scales, but seems unlikely to be the basis of adaptations that are stable over long time periods.

Epigenetic silencing of genes appears to be a key defense against transposons, the “jumping genes” discovered by Barbara McClintock. Transposons may be the ultimate “selfish” elements in our genome. A stunning 50% or more of the human genome is derived from retrotransposons , a category of transposons that copy and amplify themselves through RNA intermediates. Retrotransposons pepper our genome, moving to future generations in egg and sperm. Many originate from viruses, and most are strongly mutagenic , inserting themselves inside genes or adjacent to genes. Some 70 human genetic diseases are strongly correlated with mutations caused by the “gymnastics” of these mobile genetic elements. The relevance of epigenetics became apparent when it was found that retrotransposons are heavily methylated and silenced epigenetically, possibly as a defense against their continuous onslaught ( 21 ).

In summary, epigenetics is of paramount importance in cellular differentiation, disease, and our defenses against endogenous and freely circulating viruses. But our understanding of its full importance in evolution is in its infancy.

EARLY LIFE EVOLUTION

The ponderous gap between amino acids on the one hand, and cellular organelles, cell membranes, and self-replicating macromolecules on the other, is too great for our current theories. We are very much in the dark about the origin of life.

Stanley Miller's famous experiments in the 1950s with electrical discharges, ammonia, methane, hydrogen, water vapor, and hydrogen sulfide were discounted in the 1990s, but came into favor again in 2008 when heat from hydrothermal vent ecosystems was considered. One current hypothesis states that RNA served as a hereditary template and catalyst, and that the ribosome evolved as a “machine” for building proteins, as it does today. Research suggests that a mineral in common clay may have played a role in the synthesis of RNA. Nevertheless, early life researchers are engaged in formalized guesswork.

Darwin thought that the “tree of life” had a last universal common ancestor , now known by the acronym LUCA . Today we believe that the trunk of the tree was a heterogeneous mix of genetic entities that traded genes wantonly by horizontal gene transfer. Vertical inheritance would evolve later. Curiouser and curiouser .

INFORMATION

When DNA was found to carry the genetic code, it was realized that the information it bears is its only function . This was hard for some biologists to swallow, as it didn't sound like biochemistry. No one had ever suspected that one organic molecule could code for others, eschewing a chemical function.

A digital code was clearly at the root of life. Whereas the English alphabet has 26 letters and the Greek 24, the DNA alphabet has 4 letters. Those letters spell out 3-letter words (codons) which tell the ribosome which amino acids to assemble into proteins. Was it significant—or a stunning historical accident—that binary computer science developed at the same time that we discovered the digital code of life?

Here is the heart, the pulsing core of complexity: the informational code that runs the engine of life, the complex calculus that changes under the steady beat of natural selection. The complexity of life is hardly irreducible—we hold it in our hands, and we are learning to manipulate it at the molecular level.

With selective death as a portal, evolution changes the information in the gene pool of a species, setting the stage for reproductive isolation and the origin of new species.

CONCLUSIONS

Across biological disciplines, natural selection has become accepted as a powerful and peerless explanatory principle. It is constantly scrutinizing the smallest differences among competing alleles and their phenotypic expression and has had ample time over Earth's history to shape the life forms we see around us and in the deep fossil record. The death of the individual has been its portal for changing the gene pool of a species. Through bricolage, or tinkering, it uses old parts and constructs new machines on the palimpsest of its canvas. Biology's informational code underlies the complex dynamics of life and has only recently yielded secrets that were undreamed of by Charles Darwin. Utterly without the knowledge we have gained since he published On the Origin of Species in 1859 , Darwin gave us one of the most profound explanatory principles in the history of science.

Acknowledgments

The author is grateful to George M. Diggs, Jr., PhD, Professor of Biology, Austin College, and to Kyle E. Harms, PhD, Associate Professor of Biological Sciences, Louisiana State University, for their helpful comments and recommendations.

ENCYCLOPEDIC ENTRY

Charles darwin.

Charles Darwin and his observations while aboard the HMS Beagle , changed the understanding of evolution on Earth.

Biology, Earth Science, Geography, Physical Geography

Historic photograph of Charles Darwin in profile.

Photograph by Chronical/Alamy Stock Photo

Charles Darwin was born in 1809 in Shrewsbury, England. His father, a doctor, had high hopes that his son would earn a medical degree at Edinburgh University in Scotland, where he enrolled at the age of sixteen. It turned out that Darwin was more interested in natural history than medicine—it was said that the sight of blood made him sick to his stomach. While he continued his studies in theology at Cambridge, it was his focus on natural history that became his passion.

In 1831, Darwin embarked on a voyage aboard a ship of the British Royal Navy, the HMS Beagle, employed as a naturalist . The main purpose of the trip was to survey the coastline of South America and chart its harbors to make better maps of the region. The work that Darwin did was just an added bonus.

Darwin spent much of the trip on land collecting samples of plants, animals, rocks, and fossils . He explored regions in Brazil, Argentina, Chile, and remote islands such as the Galápagos. He packed all of his specimens into crates and sent them back to England aboard other vessels.

Upon his return to England in 1836, Darwin’s work continued. Studies of his samples and notes from the trip led to groundbreaking scientific discoveries. Fossils he collected were shared with paleontologists and geologists, leading to advances in the understanding of the processes that shape the Earth’s surface. Darwin’s analysis of the plants and animals he gathered led him to question how species form and change over time. This work convinced him of the insight that he is most famous for— natural selection . The theory of natural selection says that individuals of a species are more likely to survive in their environment and pass on their genes to the next generation when they inherit traits from their parents that are best suited for that specific environment. In this way, such traits become more widespread in the species and can lead eventually to the development of a new species .

In 1859, Darwin published his thoughts about evolution and natural selection in On the Origin of Species . It was as popular as it was controversial. The book convinced many people that species change over time—a lot of time—suggesting that the planet was much older than what was commonly believed at the time: six thousand years.

Charles Darwin died in 1882 at the age of seventy-three. He is buried in Westminster Abbey in London, England.

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Related Resources

Charles Darwin's Papers Online

For decades available only to scholars at Cambridge University Library, the private papers of Charles Darwin, one of the most influential scientists in history, can now be seen by anyone online and free of charge. This is the largest ever publication of Darwin papers and manuscripts, totalling about 20,000 items in over 100,000 electronic images.

This vast and varied collection of papers includes the first draft of his theory of evolution, notes from the voyage of the Beagle and Emma Darwin's recipe book .

We are extremely grateful for the kind permission of Cambridge University Library to reproduce these online. (See the Cambridge University Library Order Form for Digital Images .) They are presented in the same sequence as the original catalogue, which was divided mostly into bound volumes, each with a library classmark.

History of the material: The Darwin family and the Pilgrim Trust presented a magnificent collection of Darwin's papers to Cambridge University Library in 1942; they were delivered after the war. As the 1960 Handlist describes:

They were in parcels each containing small packets of manuscript wrapped in tissue paper on which the subjects had been noted in Darwin's hand. They were presumably just as Darwin left them, and accordingly this arrangement was preserved when they were bound, the volumes now representing as closely as possible Charles Darwin's papers in the order in which he left them. Beside the original papers there were copies of a large number of letters to Darwin, collections of press-cuttings, etc.

The immense value of this vast collection of material far exceeds the disadvantages of the occasional unreadable image and the lack of full colour. Several million pounds and years of production would be needed to produce colour digital images of the Darwin Archive. Hopefully this will eventually be achieved. In the meantime, most of the world's finest collection of Darwin's original manuscripts is now available for all to read, study and explore online and free of charge.

For an overview of Darwin's papers click here .

Darwin Online cannot give permission to reproduce Darwin manuscripts; enquiries about this should be addressed to Adam Perkins, Curator of Scientific Manuscripts in the University Library ( [email protected] or [email protected] )

Many individuals and institutions have helped to make Darwin Online possible, for a complete list see Acknowledgements .

The papers can be found in two ways:

1. Browse through whole volumes of Darwin's papers . Click here . 2. Search the catalogue for specific items, people, dates etc . Click here .

Darwin's first recorded doubt in 'the stability of species', from his Galapagos bird notes from the voyage of the Beagle , 1836 First sketch of the theory of evolution, 1842     Theoretical notebooks.     Drafts of Descent of Man Review of Origin of Species , 1859 Emma Darwin's recipe book. Darwin family photos

Selections from the Darwin papers

•  The first drafts of Darwin's theory of evolution: the 1842 sketch and 1844 essay. •   Darwin's papers from the Beagle voyage. Click here . •   Darwin's religious views: Emma Darwin's 1839 memo , and an entire volume on the subject. Click here . •   Drafts of Darwin's unpublished 'big book', Natural selection. Click here . •   Notes & drafts for his book Descent of Man . Click here . •   Unpublished photos collected for Expression of the Emotions . Click here . •   Reviews of Darwin's works. Click here . •   Darwin and experimentation on animals. Click here . •   Caricatures, cartoons & sketches of Darwin. Click here and here . •   Darwin's accounts with his publisher John Murray for 1881. Click here . •   Obituaries of Charles Darwin, Click here , here and here . •   Items in French , German , Spanish or Italian .

See a list of all available online images of Darwin's papers. Click here .

See Darwin's handwriting beside a typed version:

[ Beagle animal notes (1832-33)]. Text & images 'Chiloe Jan r . 1835' [ Beagle notes]. Text & images 'The position of the bones of Mastodon (?) at Port St Julian is of interest'. Text & images [Darwin's personal 'Journal' (1809-1881)]. Text & images [An autobiographical fragment] (08.1838). Text & images 'Our poor child, Annie' [Darwin's reminiscence of Anne Elizabeth Darwin] (30.04.1851). Text & images Part of Darwin's 'autobiography', 1876

The collection is organized into categories:

•   Abstract — Darwin's reading notes. •   Draft — Darwin's rough drafts of his many publications. •   Figure — Drawings, diagrams and tables. •   Note — Includes most of Darwin's notes, usually organized into subject portfolios. •   Photo — Photographs. •   Printed — Published items such as reviews of Darwin's works or clippings he collected for his researches. •   Miscellaneous  

Read about the reception of the launch of Darwin's papers here .

John van Wyhe

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1859: Darwin Published On the Origin of Species, Proposing Continual Evolution of Species

1859: darwin published on the origin of species , proposing continual evolution of species.

Darwin's exploratory survey on the H.M.S. Beagle had brought him into contact with a wide variety of living organisms and fossils. The adaptations he saw in the finches and tortoises on the Galapagos Islands struck him particularly acutely. Darwin concluded that species change through natural selection, or - to use Wallace's phrase - through "the survival of the fittest" in a given environment.

Darwin's book immediately attracted attention and controversy, not only from the scientific community, but also from the general public, who were ignited by the social and religious implications of the theory. Darwin eventually produced six editions of this book.

In time, a growing understanding of genetics and of the fact that genes inherited from both parents remain distinct entities - even if the characteristics of parents appear to blend in their children - explained how natural selection could work and helped vindicate Darwin's proposal.

Charles Darwin's On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life remains in print, in many languages.

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Darwin Archive

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Charles Darwin (1809-1882) graduated from the University of Cambridge in 1831 and was recommended by the Professor of Botany John Stevens Henslow to Robert Fitzroy, commander of HM Sloop Beagle , as a naturalist to sail on a hydrographical voyage Fitzroy was to make in South American waters.  Returning from the Beagle circumnavigation in 1836, Darwin published  Journal of Researches... during the Voyage of HMS Beagle , soon married his cousin Emma Wedgwood and in 1842 moved to the Kent village of Down, where he spent the rest of his life.  Darwin was living at Down House when he published On the Origin of Species by means of Natural Selection... , 1859, as well as a series of monographs in botany, entomology and anthropology.

The collection of Charles Darwin's papers at the University Library originates in the work of his son Francis who collected as many of Charles's letters and papers as possible, which remained in the family after Francis died.  In 1942 the Pilgrim Trust and the Darwin family gave most of these papers to the University Library, which were actually transferred in 1948. (Another portion were given to the museum recently established at Down House.) In 1975 the Library acquired an important supplementary collection of Darwin papers hitherto retained by Sir Robin Darwin and in 1991 George Pember Darwin made a gift of considerably more material.  Over the years, further papers have been acquired by gift from the Darwin family, by other deposits, and by purchase; the collection is accruing continually. 

Catalogues of the Darwin papers and libary and some related family collections are available in the Manuscripts Reading Room and online on the ArchiveSearch database, along with digital versions and transcriptions of selected manuscripts and annotated publications from Charles Darwin's library collection, also held by the Department of Manuscripts. Darwin's letters to 1876 including those held at Cambridge University Library and elsewhere have been published as the  Correspondence of Charles Darwin  volumes 1 to 24 (1985-2017) by the Darwin Correspondence Project at Cambridge University Library.  A fully searchable calendar of the 15,000 known letters is available via the Darwin Correspondence Project website, along with transcriptions of complete texts of the letters to 1872. Both projects are ongoing and continue to publish new digital material online with the Darwin Correspondence Project scheduled to publish all of the known letters by 2022. 

Readers interested in the letters sent and received by Darwin and his key manuscripts but unfamiliar with the Darwin collections are advised to consult this work before applying to the Library for permission to see the original papers. 

In broad terms, classmarks MSS.DAR.1-DAR.28 are assigned to papers relating to his publications, MSS.DAR.29-DAR.42 to papers concerned with the zoology and geology of the Beagle voyage.  Letters and notes are in MSS.DAR.43-DAR.52.  MSS.DAR.53-DAR.90 include further manuscripts concerning publications, together with much associated correspondence.  MSS.DAR.91-DAR.118 contain correspondence, MSS.DAR.119-DAR.130 represent various notebooks, while MSS.DAR.131-DAR.141 have records relating to Darwin’s published papers and his work.  MS.DAR.142 is a collection of specimen seeds.  MSS.DAR.143-DAR.156 has further letters and MS.DAR.157 a few folios of the On the Origin of Species manuscript, this completing the collection as listed in 1960.  Of the supplementary papers, MS.DAR.158 is Darwin's Journal , MSS.DAR.159-DAR.184 contain further correspondence, MS.DAR.185 and MS.DAR.186 miscellaneous accessions, MSS.DAR.187-DAR.197 notes and papers relating to publications, MSS.DAR.198-DAR.205 further letters, MSS.DAR.206-DAR.209 experiments and notes, MS.DAR.210 and MS.DAR.211 more letters, while MS.DAR.212 and MS.DAR.213 have manuscripts and proofs of publications.  The remaining classes, MSS.DAR.214-DAR.272, are assigned to the papers of family members and other miscellaneous deposits, including photographs; MS.DAR.251 has a large collection of the correspondence of George Howard Darwin, it should be noted.

There are collections of important associated manuscripts in the University Library, notably, at MS Add. 7983-7984 , the sketch books of Conrad Martens, who sailed with Darwin during part of the Beagle voyage, and, at MS Add.8853 , the papers of Robert Fitzroy.  Prospective readers may wish to be aware that there are Darwin family and scientific papers for Francis Darwin MS Add. 8187-8188 , George Howard Darwin  MS Add. 5749-5750 , 8166 , 7909 ,  Emma Nora Barlow (née Emma Nora Darwin)  MS.Add.8904 , Gwen and Jacques Raverat (Gwen, née Gwendoline Mary Darwin), MS Add. 9209 , 9268 and Ida and Horace Darwin (Ida, née Emma Cecilia Farrer), MS Add. 9368 as well as the papers of the Cambridge Scientific Instrument Company  founded by Horace Darwin. There are also papers of founding editor of the Darwin Correspondence Project, Sydney Smith  MS Add. 8895  and papers relating to psychologist John Bowlby's biography of Darwin  MS Add. 8884 .

Additional references 

Handlist of Darwin Papers at the University Library, Cambridge (1960), lists the papers in the 1942 gift.

Supplementary Handlist of the Papers of Charles Darwin  lists acquisitions since 1960

Frederick Burkhardt and Sydney Smith (editors),  A calendar of the correspondence of Charles Darwin, 1821-1882, with supplement , Cambridge, 1994. 

Contact: Liz Smith , Digital Curator for Nineteenth Century Science Collections (01223 747403; [email protected] ).

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