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The origin of life on Earth, explained

The origin of life on Earth stands as one of the great mysteries of science. Various answers have been proposed, all of which remain unverified. To find out if we are alone in the galaxy, we will need to better understand what geochemical conditions nurtured the first life forms. What water, chemistry and temperature cycles fostered the chemical reactions that allowed life to emerge on our planet? Because life arose in the largely unknown surface conditions of Earth’s early history, answering these and other questions remains a challenge.

Several seminal experiments in this topic have been conducted at the University of Chicago, including the Miller-Urey experiment that suggested how the building blocks of life could form in a primordial soup.

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• When did life on Earth begin?

Where did life on Earth begin?

What are the ingredients of life on earth, what are the major scientific theories for how life emerged, what is chirality and why is it biologically important, what research are uchicago scientists currently conducting on the origins of life, when did life on earth begin .

Earth is about 4.5 billion years old. Scientists think that by 4.3 billion years ago, Earth may have developed conditions suitable to support life. The oldest known fossils, however, are only 3.7 billion years old. During that 600 million-year window, life may have emerged repeatedly, only to be snuffed out by catastrophic collisions with asteroids and comets.

The details of those early events are not well preserved in Earth’s oldest rocks. Some hints come from the oldest zircons, highly durable minerals that formed in magma. Scientists have found traces of a form of carbon—an important element in living organisms— in one such 4.1 billion-year-old zircon . However, it does not provide enough evidence to prove life’s existence at that early date.

Two possibilities are in volcanically active hydrothermal environments on land and at sea.

Some microorganisms thrive in the scalding, highly acidic hot springs environments like those found today in Iceland, Norway and Yellowstone National Park. The same goes for deep-sea hydrothermal vents. These chimney-like vents form where seawater comes into contact with magma on the ocean floor, resulting in streams of superheated plumes. The microorganisms that live near such plumes have led some scientists to suggest them as the birthplaces of Earth’s first life forms.

Organic molecules may also have formed in certain types of clay minerals that could have offered favorable conditions for protection and preservation. This could have happened on Earth during its early history, or on comets and asteroids that later brought them to Earth in collisions. This would suggest that the same process could have seeded life on planets elsewhere in the universe.

The recipe consists of a steady energy source, organic compounds and water.

Sunlight provides the energy source at the surface, which drives photosynthesis. On the ocean floor, geothermal energy supplies the chemical nutrients that organisms need to live.

Also crucial are the elements important to life . For us, these are carbon, hydrogen, oxygen, nitrogen, and phosphorus. But there are several scientific mysteries about how these elements wound up together on Earth. For example, scientists would not expect a planet that formed so close to the sun to naturally incorporate carbon and nitrogen. These elements become solid only under very cold temperatures, such as exist in the outer solar system, not nearer to the sun where Earth is. Also, carbon, like gold, is rare at the Earth’s surface. That’s because carbon chemically bonds more often with iron than rock. Gold also bonds more often with metal, so most of it ends up in the Earth’s core. So, how did the small amounts found at the surface get there? Could a similar process also have unfolded on other planets?

The last ingredient is water. Water now covers about 70% of Earth’s surface, but how much sat on the surface 4 billion years ago? Like carbon and nitrogen, water is much more likely to become a part of solid objects that formed at a greater distance from the sun. To explain its presence on Earth, one theory proposes that a class of meteorites called carbonaceous chondrites formed far enough from the sun to have served as a water-delivery system.

There are several theories for how life came to be on Earth. These include:

Life emerged from a primordial soup

As a University of Chicago graduate student in 1952, Stanley Miller performed a famous experiment with Harold Urey, a Nobel laureate in chemistry. Their results explored the idea that life formed in a primordial soup.

Miller and Urey injected ammonia, methane and water vapor into an enclosed glass container to simulate what were then believed to be the conditions of Earth’s early atmosphere. Then they passed electrical sparks through the container to simulate lightning. Amino acids, the building blocks of proteins, soon formed. Miller and Urey realized that this process could have paved the way for the molecules needed to produce life.

Scientists now believe that Earth’s early atmosphere had a different chemical makeup from Miller and Urey’s recipe. Even so, the experiment gave rise to a new scientific field called prebiotic or abiotic chemistry, the chemistry that preceded the origin of life. This is the opposite of biogenesis, the idea that only a living organism can beget another living organism.

Seeded by comets or meteors

Some scientists think that some of the molecules important to life may be produced outside the Earth. Instead, they suggest that these ingredients came from meteorites or comets.

“A colleague once told me, ‘It’s a lot easier to build a house out of Legos when they’re falling from the sky,’” said Fred Ciesla, a geophysical sciences professor at UChicago. Ciesla and that colleague, Scott Sandford of the NASA Ames Research Center, published research showing that complex organic compounds were readily produced under conditions that likely prevailed in the early solar system when many meteorites formed.

Meteorites then might have served as the cosmic Mayflowers that transported molecular seeds to Earth. In 1969, the Murchison meteorite that fell in Australia contained dozens of different amino acids—the building blocks of life.

Comets may also have offered a ride to Earth-bound hitchhiking molecules, according to experimental results published in 2001 by a team of researchers from Argonne National Laboratory, the University of California Berkeley, and Lawrence Berkeley National Laboratory. By showing that amino acids could survive a fiery comet collision with Earth, the team bolstered the idea that life’s raw materials came from space.

In 2019, a team of researchers in France and Italy reported finding extraterrestrial organic material preserved in the 3.3 billion-year-old sediments of Barberton, South Africa. The team suggested micrometeorites as the material’s likely source. Further such evidence came in 2022 from samples of asteroid Ryugu returned to Earth by Japan’s Hayabusa2 mission. The count of amino acids found in the Ryugu samples now exceeds 20 different types .

In 1953, UChicago researchers published a landmark paper in the Journal of Biological Chemistry that marked the discovery of the pro-chirality concept , which pervades modern chemistry and biology. The paper described an experiment showing that the chirality of molecules—or “handedness,” much the way the right and left hands differ from one another—drives all life processes. Without chirality, large biological molecules such as proteins would be unable to form structures that could be reproduced.

Today, research on the origin of life at UChicago is expanding. As scientists have been able to find more and more exoplanets—that is, planets around stars elsewhere in the galaxy—the question of what the essential ingredients for life are and how to look for signs of them has heated up.

Nobel laureate Jack Szostak joined the UChicago faculty as University Professor in Chemistry in 2022 and will lead the University’s new interdisciplinary Origins of Life Initiative to coordinate research efforts into the origin of life on Earth. Scientists from several departments of the Physical Sciences Division are joining the initiative, including specialists in chemistry, astronomy, geology and geophysics.

“Right now we are getting truly unprecedented amounts of data coming in: Missions like Hayabusa and OSIRIS-REx are bringing us pieces of asteroids, which helps us understand the conditions that form planets, and NASA’s new JWST telescope is taking astounding data on the solar system and the planets around us ,” said Prof. Ciesla. “I think we’re going to make huge progress on this question.”

Last updated Sept. 19, 2022.

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The history of life: looking at the patterns

The central ideas of evolution are that life has a history — it has changed over time — and that different species share common ancestors.

Here, you can explore how evolutionary change and evolutionary relationships are represented in “family trees,” how these trees are constructed, and how this knowledge affects biological classification. You will also find a timeline of evolutionary history and information on some specific events in the history of life: human evolution and the origin of life.

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1.1.3.1: Evolution of Life

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This timeline shows the history of life on Earth. In the entire span of the time, humans are a relatively new addition.

Today, the most accepted theory of life on Earth is evolution, and there is a vast amount of evidence supporting this theory. However, this wasn’t always the case.

An introduction to evolution and natural selection can be viewed at http ://www.youtube.com/watch?v=GcjgWov7mTM .

As you view Introduction to Evolution and Natural Selection, focus on these concepts: the relationship between evolution and natural selection, the relationship between natural selection and variation, the evolution of the peppered moth.

Darwin and the Theory of Evolution

The idea of evolution has been around for centuries. In fact, it goes all the way back to the ancient Greek philosopher Aristotle. However, evolution is most often associated with Charles Darwin . Darwin published a book on evolution in 1859 titled On the Origin of Species . In the book, Darwin stated the theory of evolution by natural selection. He also presented a great deal of evidence that evolution occurs.

Evolution is a change in the characteristics of living things over time. As described by Darwin, evolution occurs by a process called natural selection . In natural selection, some members of a species, being better adapted or suited to their environment, produce more offspring than others, so they pass "advantageous traits" to their offspring. Over many generations, this can lead to major changes in the characteristics of the species. Evolution explains how living things are changing today and how modern living things have descended from ancient life forms that no longer exist on Earth. As living things evolve, they generally become better suited for their environment. This is because they evolve adaptations. An adaptation is a trait that helps an organism survive and reproduce in a given environment.

Despite all the evidence Darwin presented, his theory was not well-received at first. Many people found it hard to accept the idea that humans had evolved from an ape-like ancestor, and they saw evolution as a challenge to their religious beliefs. Look at the cartoon in Figure below . Drawn in 1871, it depicts Darwin himself as an ape. The cartoon reflects how many people felt about Darwin and his theory during his own time. Darwin had actually expected this type of reaction to his theory and had waited a long time before publishing his book for this reason. It was only when another scientist, named Alfred Russel Wallace, developed essentially the same theory of evolution that Darwin put his book into print.

Charles Darwin’s name is linked with the theory of evolution. This cartoon from the 1870s makes fun of both Darwin and his theory.

Although Darwin presented a great deal of evidence for evolution in his book, he was unable to explain how evolution occurs. That’s because he knew nothing about genes. As a result, he didn’t know how characteristics are passed from parents to offspring, let alone how they could change over time.

Evolutionary Theory After Darwin

Since Darwin’s time, scientists have gathered even more evidence to support the theory of evolution. Some of the evidence comes from fossils , and some comes from studies that show how similar living things are to one another. By the 1930s, scientists had also learned about genes. As a result, they could finally explain how characteristics of organisms could pass from one generation to the next and change over time.

Using modern technology, scientists can now directly compare the genes of living species . The more genes different species share in common, the more closely related the species are presumed to be. Consider humans and chimpanzees. They share about 98% of their genes. This means that they shared a common ancestor in the not-too-distant past. This is just one of many pieces of evidence that show we are part of the evolution of life on Earth.

Misconceptions About Evolution

Today, evolution is still questioned by some people. Often, people who disagree with the theory of evolution do not really understand it. For example, some people think that the theory of evolution explains how life on Earth first began. In fact, the theory explains only how life changed after it first appeared. Some people think the theory of evolution means that humans evolved from modern apes. In fact, the theory suggests humans and modern apes have a common ancestor that lived several million years ago. These and other misconceptions about evolution contribute to the controversy that still surrounds this fundamental principle of biology.

• Life began on Earth at least 3.5 to 4 billion years ago, and it has been evolving ever since.
• Darwin stated the theory of evolution by natural selection, presenting a great deal of evidence to support his theory.
• Evolution is a change in the characteristics of living things over time. Evolution occurs by natural selection.
• Characteristics of organisms are passed from one generation to the next through their genes.

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• What is the end result of this process?
• What three things are necessary for evolution by natural selection?
• What is evolution?
• What is natural selection?
• Briefly, explain the theory of evolution.

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• INNOVATIONS IN
• 09 May 2018

How Did Life Begin?

• Jack Szostak 0

Jack Szostak is a professor of genetics at Harvard Medical School and one of the recipients of the 2009 Nobel Prize in Physiology or Medicine.

You can also search for this author in PubMed   Google Scholar

Illustration by Chris Gash

Is the existence of life on Earth a lucky fluke or an inevitable consequence of the laws of nature? Is it simple for life to emerge on a newly formed planet, or is it the virtually impossible product of a long series of unlikely events? Advances in fields as disparate as astronomy, planetary science and chemistry now hold promise that answers to such profound questions may be around the corner. If life turns out to have emerged multiple times in our galaxy, as scientists are hoping to discover, the path to it cannot be so hard. Moreover, if the route from chemistry to biology proves simple to traverse, the universe could be teeming with life.

The discovery of thousands of exoplanets has sparked a renaissance in origin-of-life studies. In a stunning surprise, almost all the newly discovered solar systems look very different from our own. Does that mean something about our own, very odd, system favors the emergence of life? Detecting signs of life on a planet orbiting a distant star is not going to be easy, but the technology for teasing out subtle “biosignatures” is developing so rapidly that with luck we may see distant life within one or two decades.

Innovations In The Biggest Questions In Science

To understand how life might begin, we first have to figure out how—and with what ingredients—planets form. A new generation of radio telescopes, notably the Atacama Large Millimeter/submillimeter Array in Chile’s Atacama Desert, has provided beautiful images of protoplanetary disks and maps of their chemical composition. This information is inspiring better models of how planets assemble from the dust and gases of a disk. Within our own solar system, the Rosetta mission has visited a comet, and OSIRIS-REx will visit, and even try to return samples from, an asteroid, which might give us the essential inventory of the materials that came together in our planet.

Once a planet like our Earth—not too hot and not too cold, not too dry and not too wet—has formed, what chemistry must develop to yield the building blocks of life? In the 1950s the iconic Miller-Urey experiment, which zapped a mixture of water and simple chemicals with electric pulses (to simulate the impact of lightning), demonstrated that amino acids, the building blocks of proteins, are easy to make. Other molecules of life turned out to be harder to synthesize, however, and it is now apparent that we need to completely reimagine the path from chemistry to life. The central reason hinges on the versatility of RNA, a very long molecule that plays a multitude of essential roles in all existing forms of life. RNA can not only act like an enzyme, it can also store and transmit information. Remarkably, all the protein in all organisms is made by the catalytic activity of the RNA component of the ribosome, the cellular machine that reads genetic information and makes protein molecules. This observation suggests that RNA dominated an early stage in the evolution of life.

Today the question of how chemistry on the infant Earth gave rise to RNA and to RNA-based cells is the central question of origin-of-life research. Some scientists think that life originally used simpler molecules and only later evolved RNA. Other researchers, however, are tackling the origin of RNA head-on, and exciting new ideas are revolutionizing this once quiet backwater of chemical research. Favored geochemical scenarios involve volcanic regions or impact craters, with complex organic chemistry, multiple sources of energy, and dynamic light-dark, hot-cold and wet-dry cycles. Strikingly, many of the chemical intermediates on the way to RNA crystallize out of reaction mixtures, self-purifying and potentially accumulating on the early Earth as organic minerals—reservoirs of material waiting to come to life when conditions change.

Assuming that key problem is solved, we will still need to understand how RNA was replicated within the first primitive cells. Researchers are just beginning to identify the sources of chemical energy that could enable the RNA to copy itself, but much remains to be done. If these hurdles can also be overcome, we may be able to build replicating, evolving RNA-based cells in the laboratory—recapitulating a possible route to the origin of life.

What next? Chemists are already asking whether our kind of life can be generated only through a single plausible pathway or whether multiple routes might lead from simple chemistry to RNA-based life and on to modern biology. Others are exploring variations on the chemistry of life, seeking clues as to the possible diversity of life “out there” in the universe. If all goes well, we will eventually learn how robust the transition from chemistry to biology is and therefore whether the universe is full of life-forms or—but for us—sterile.

Illustration by Matthew Twombly

Nature 557 , S13-S15 (2018)

doi: https://doi.org/10.1038/d41586-018-05098-w

This article is part of Innovations In The Biggest Questions In Science , an editorially independent supplement produced with the financial support of third parties. About this content .

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• Introduction to Human Evolution

Human evolution

Human evolution is the lengthy process of change by which people originated from apelike ancestors. Scientific evidence shows that the physical and behavioral traits shared by all people originated from apelike ancestors and evolved over a period of approximately six million years.

One of the earliest defining human traits, bipedalism -- the ability to walk on two legs -- evolved over 4 million years ago. Other important human characteristics -- such as a large and complex brain, the ability to make and use tools, and the capacity for language -- developed more recently. Many advanced traits -- including complex symbolic expression, art, and elaborate cultural diversity -- emerged mainly during the past 100,000 years.

Humans are primates. Physical and genetic similarities show that the modern human species, Homo sapiens , has a very close relationship to another group of primate species, the apes. Humans and the great apes (large apes) of Africa -- chimpanzees (including bonobos, or so-called “pygmy chimpanzees”) and gorillas -- share a common ancestor that lived between 8 and 6 million years ago. Humans first evolved in Africa, and much of human evolution occurred on that continent. The fossils of early humans who lived between 6 and 2 million years ago come entirely from Africa.

Most scientists currently recognize some 15 to 20 different species of early humans. Scientists do not all agree, however, about how these species are related or which ones simply died out. Many early human species -- certainly the majority of them – left no living descendants. Scientists also debate over how to identify and classify particular species of early humans, and about what factors influenced the evolution and extinction of each species.

Early humans first migrated out of Africa into Asia probably between 2 million and 1.8 million years ago. They entered Europe somewhat later, between 1.5 million and 1 million years. Species of modern humans populated many parts of the world much later. For instance, people first came to Australia probably within the past 60,000 years and to the Americas within the past 30,000 years or so. The beginnings of agriculture and the rise of the first civilizations occurred within the past 12,000 years.

Paleoanthropology

Paleoanthropology is the scientific study of human evolution. Paleoanthropology is a subfield of anthropology, the study of human culture, society, and biology. The field involves an understanding of the similarities and differences between humans and other species in their genes, body form, physiology, and behavior. Paleoanthropologists search for the roots of human physical traits and behavior. They seek to discover how evolution has shaped the potentials, tendencies, and limitations of all people. For many people, paleoanthropology is an exciting scientific field because it investigates the origin, over millions of years, of the universal and defining traits of our species. However, some people find the concept of human evolution troubling because it can seem not to fit with religious and other traditional beliefs about how people, other living things, and the world came to be. Nevertheless, many people have come to reconcile their beliefs with the scientific evidence.

Early human fossils and archeological remains offer the most important clues about this ancient past. These remains include bones, tools and any other evidence (such as footprints, evidence of hearths, or butchery marks on animal bones) left by earlier people. Usually, the remains were buried and preserved naturally. They are then found either on the surface (exposed by rain, rivers, and wind erosion) or by digging in the ground. By studying fossilized bones, scientists learn about the physical appearance of earlier humans and how it changed. Bone size, shape, and markings left by muscles tell us how those predecessors moved around, held tools, and how the size of their brains changed over a long time. Archeological evidence refers to the things earlier people made and the places where scientists find them. By studying this type of evidence, archeologists can understand how early humans made and used tools and lived in their environments.

The process of evolution

The process of evolution involves a series of natural changes that cause species (populations of different organisms) to arise, adapt to the environment, and become extinct. All species or organisms have originated through the process of biological evolution. In animals that reproduce sexually, including humans, the term species refers to a group whose adult members regularly interbreed, resulting in fertile offspring -- that is, offspring themselves capable of reproducing. Scientists classify each species with a unique, two-part scientific name. In this system, modern humans are classified as Homo sapiens .

Evolution occurs when there is change in the genetic material -- the chemical molecule, DNA -- which is inherited from the parents, and especially in the proportions of different genes in a population. Genes represent the segments of DNA that provide the chemical code for producing proteins. Information contained in the DNA can change by a process known as mutation. The way particular genes are expressed – that is, how they influence the body or behavior of an organism -- can also change. Genes affect how the body and behavior of an organism develop during its life, and this is why genetically inherited characteristics can influence the likelihood of an organism’s survival and reproduction.

Evolution does not change any single individual. Instead, it changes the inherited means of growth and development that typify a population (a group of individuals of the same species living in a particular habitat). Parents pass adaptive genetic changes to their offspring, and ultimately these changes become common throughout a population. As a result, the offspring inherit those genetic characteristics that enhance their chances of survival and ability to give birth, which may work well until the environment changes. Over time, genetic change can alter a species' overall way of life, such as what it eats, how it grows, and where it can live. Human evolution took place as new genetic variations in early ancestor populations favored new abilities to adapt to environmental change and so altered the human way of life.

Dr. Rick Potts provides a video short introduction to some of the evidence for human evolution, in the form of fossils and artifacts.

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How did life begin?

Some things are alive and some things are not. Seems like an easy and obvious concept, but drawing the line that separates “alive” from “not alive” is not quite as straightforward as you might think. What makes something alive? Well, if you Google “properties of life,” you will see that there are seven (or eight, or nine, or maybe even ten) things that everyone “agrees” are key—things like growth, the ability to reproduce, response to stimuli and the environment, maintaining homeostasis, and, often, cellular organization.

So, a quick quiz.  A rock? Not alive. An oak tree? Alive. Water? Not alive. Single-celled bacteria? Alive. An RNA virus? Well, now things get interesting.

Most viruses are simple. They are composed of an outer shell or membrane that surrounds some genetic material: sometimes DNA, sometimes RNA, sometimes both. They generally can’t, however, reproduce on their own—one of the essential properties of life. Instead, they co-opt the reproduction machinery of the cells they infect, making the cell make more viruses. So, there is some disagreement among scientists about whether viruses count as alive or not, but because they contain genetic material, they are, at least, likely to be related to other life on Earth. All life that we know of shares the use of DNA or RNA to carry genetic information, which suggests a shared origin; viruses are somehow connected to the evolutionary tree of life—which brings us to a second line between life and no life.

If we think about the history of the Earth, at some point in the past there was no life and now the place is practically bursting at the seams with it. How did that happen? That is a question that has perplexed humanity for millennia. Two Eberly College of Science researchers have brought the diverse expertise of their labs together to explore some possible answers.

Life in its simplest form could be thought of as a collection of molecules that perform chemical reactions and that are somehow compartmentalized, isolating them from their environment. Christine Keating , professor of chemistry, studies physical chemistry and the self-assembly of molecules. As an undergrad she studied chemistry and biology, so she gravitated toward studying the materials chemistry of life and how cells might have evolved. Phil Bevilacqua , head of the Department of Chemistry and Distinguished Professor of Chemistry and of Biochemistry and Molecular Biology, has been studying RNA for nearly 30 years. RNA can both carry genetic information and perform chemical reactions, making it an attractive candidate for playing a role in early life.

“There was this old Reese’s Peanut Butter Cup commercial where one person had chocolate and another had peanut butter and they bumped into each other,” said Keating. “The chocolate got into the peanut butter and they were like, ‘This is amazing.’ I think of our collaboration like one of us had the chocolate and one of us had the peanut butter. Our research really complements each other’s to be able to look at possible scenarios for the evolution of early life.”

It’s an RNA world

Or at least it was. Maybe.

“How life actually began is basically unknowable,” said Bevilacqua. “There is no fossil record of the early steps that led to life, and we can’t go back to observe what was going on. What we can do, though, is use what we know about the Earth three to four billion years ago and what we know about the simplest forms of life to build models and test hypotheses. We can begin to narrow down what might have been possible and eliminate ideas that probably aren’t.”

One of the leading hypotheses about the origin of life on Earth leans heavily on the role of RNA. RNA is DNA’s lesser known little brother; it stands for ribonucleic acid (DNA is deoxyribonucleic acid ). Both molecules are long strings composed of four basic subunits, and it’s the sequence of these units that encodes genetic information.

The four subunits of DNA are adenine, thymine, cytosine, and guanine; they are called nucleotides or bases, but we often just refer to them as A, T, C, and G. The DNA molecule is double stranded. Think of a twisted ladder: The side rails of the ladder are the two strands, and the rungs represent the bonds that hold them together. The two strands are complementary to each other: If there is an A on one side of the rung, the other side will have a T; and if there is a C on one side, the other will have a G.

RNA shares three of the four subunits with DNA but has uracil (U) instead of thymine (T) and is single stranded. Because sections of the RNA molecule can be complementary to other sections, the molecule can fold up on itself, bonding in a way similar to double-stranded DNA, with U complementing A. The resulting three-dimensional structures of RNA molecules can allow it to do more than just encode information; it can carry out functions that are nowadays mostly associated with proteins.

“RNA became implicated in early life scenarios in the late 1960s,” said Bevilacqua. “It was recognized that the complex structures that RNA forms could potentially perform catalysis—it could drive chemical reactions. So, you have a single molecule that sort of solved the ‘chicken and egg’ question of which came first in the origin of life: genetic information or catalysis? Work in the 1980s that led to a Nobel Prize demonstrated that RNA can in fact do both, so it became a prime candidate for how early life could have evolved in what is known as the RNA world hypothesis .”

The research in Bevilacqua’s lab focuses on understanding the functions of RNA at the molecular level. His group studies the mechanisms of RNA enzymes—RNA molecules that have functions similar to protein enzymes in chemical reactions—known as ribozymes . Their research helped to establish the role played by ribozymes in proton transfer and RNA cleavage, and they are currently studying the role of metal ions and other cofactors in these mechanisms. They also study the precise mechanisms of how RNA molecules fold in cells. Studying the role of RNA in early life came later.

“Because I work on RNA catalysis, I’ve always been interested in its potential role in early life, but I never took it too seriously,” said Bevilacqua. “It would come up as the last sentence of a discussion in a paper: ‘This versatility of RNA to perform reactions could relate to the RNA world hypothesis.’ But in thinking of what it would take to go from a bunch of molecules floating around with the ability to perform reactions to something that could be called early life, I started to work with Chris, putting together her expertise in protocells with my expertise in RNA.”

Compartmentalize it!

If you think about a modern cell with its hundreds of components—organelles, proteins, DNA, and RNA—working together seamlessly to perform its varied functions, it can be hard to imagine how it could have evolved. But we know that it must have. Before there were modern cells, there had to be earlier, simpler ones. And before that, there had to exist the components to form them.

We can imagine an early, prelife Earth in which chemical reactions are occurring that begin to produce molecules that resemble things like RNA. But even if these early molecules could potentially encode genetic information and perform catalysis, they would be floating around in the proverbial primordial soup, and the chance they would find each other and actually do these things seems incredibly slim. A necessary step, therefore, in the early evolution of what would become life was to increase the chances that these molecules would come together where they could begin to interact in more and more-complex ways. One way to do that was to compartmentalize them.

“We were studying the self-assembly of molecules, what molecules can do on their own, and it’s kind of amazing what you get for free,” said Keating. “An example is lipid self-assembly. Lipids are fatty compounds that are insoluble in water. If you have some lipids and you add water—boom! Vesicles form. It’s amazing to watch.”

Among other things, Keating’s group studies artificial cells. Somewhat counterintuitively, she decided to start by recreating the cell’s cytoplasm—the goo on the inside that is often ignored—rather than its membrane. Even without membranes, you could get compartments through liquid-liquid phase separation.

“We always knew that if we were going to make artificial cells, it needed to be in a way that we could learn about real cells,” said Keating. “So, starting with the cytoplasm—where everything within the cell takes place—made sense, even though people may think it’s the boring part. We were kind of amazed at how quickly things got interesting.”

Macromolecules (big molecules—like RNA, for example) would concentrate into different liquid phases within the artificial cytoplasm.

“Without really trying, we found a solution to one of the big problems in studying the origin of life, which is, ‘How do you put stuff in your compartment?’” said Keating. “You can make a membrane really easily, like with lipids, but it’s incredibly difficult to get things inside of them. With our system, you get these phase-separated droplets—called coacervates —in which macromolecules collect, and you can concentrate them from a really dilute solution. What better to study in this system than RNA, which is where Phil comes in.”

Two great tastes that taste great together

“Working with Chris, we really started to think about how it all began, how did life start, how do you compartmentalize molecules to facilitate the types of reactions we were studying,” said Bevilacqua. “We began to look at what’s possible, and not only that but what would be feasible and probable. I was coming from one angle and she was coming from another, and there was a confluence of our two approaches that really made sense.”

The collaboration is already paying dividends. Recently, the two groups published a paper demonstrating that not only could RNA be assembled from its constituent parts inside of membraneless compartments but the concentration of the RNAs in the compartments also enhanced the enzymatic activity of ribozymes.

Whether or not these particular steps actually took place during life’s evolution on Earth, the collaboration of Keating’s and Bevilacqua’s research groups is advancing our understanding of what might have happened. They go together like chocolate and peanut butter.  

“I’d like to lay claim to being the chocolate in the Reese’s cup,” said Keating.

Volume 5 Supplement 3

Origin and Early Evolution of Life

• INTRODUCTION TO THE SPECIAL ISSUE: Origin of Life
• Open access
• Published: 27 September 2012

The Origin and Early Evolution of Life: Where, When and How?

• Antonio Lazcano 1  

Evolution: Education and Outreach volume  5 ,  pages 334–336 ( 2012 ) Cite this article

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Although it is frequently taught in many schools and universities all over the world that since early antiquity philosophers and naturalists alike appealed to spontaneous generation to explain the origin of life, this was not really the case. Until the development of microscopes in the seventeenth century, spontaneous generation was seen mostly as a nonsexual reproductive mechanism of insects, maggots, and what were called “lower animals.” The extraordinary descriptions of a microbial world by Anton van Leewenhoek and others opened an unsuspected dimension to the possibility of spontaneous generation, but it was not it was not until Georges Louis Leclerc de Buffon and Jean-Baptiste de Lamarck incorporated it within their transformist schemes that it was seen as the mechanism that had led to the first appearance of life on Earth.

Like his paternal grandfather and scientific predecessor Erasmus Darwin, Charles Darwin was convinced that plants and animals arose naturally from simple nonliving inorganic compounds. With very few exceptions, he carefully avoided discussing this possibility in his books. In private, however, he was much less restrained, as shown by the letter that he sent in February 1871 to Francis Hooker, in which he famously wrote, “…it is often said that all the conditions for the first production of a living organism are now present, which could ever have been present. But if (and oh what a big if) we could conceive in some warm little pond with all sorts of ammonia and phosphoric salts,–light, heat, electricity &c. present, that a protein compound was chemically formed, ready to undergo still more complex changes, at the present day such matter w d be instantly devoured, or absorbed, which would not have been the case before living creatures were formed.”

As discussed by Juli Peretó and Jesus Catalá in this issue of Evolution: Education and Outreach , Darwin’s reluctance to address in public the origin of life surprised many of his friends and followers, who argued quite emphatically that Darwin’s theory was incomplete until it could account for the origin of life. The list included Ernest Haeckel, whose widely read books popularized Darwin’s theory and advocated that the possibility that living organisms were the evolutionary outcome of the gradual transformation of lifeless gel-like matter into protoplasm, endowed with the ability to fix atmospheric CO 2 , in the early atmosphere, which was a widespread notion even during Darwin’s lifetime.

Equally significant, toward the end of the nineteenth century, the chemical gap separating nonliving from living matter had been bridged at least in part by the laboratory syntheses of organic molecules, which for a long time had been considered to be fundamentally different from inorganic compounds. This view soon merged with the emergent fields of biochemistry and cell biology, leading to proposals in which the origin of protoplasm was equated with the origin of life. Some of these hypotheses considered life as an emergent feature of nature and attempted to understand its origin by introducing principles of historical explanation, but most of these explanations went unnoticed, in part because they were incomplete, speculative schemes largely devoid of direct evidence and not subject to fruitful experimental testing.

This changed during the 1920s, when Alexander I. Oparin, a young Russian biochemist, proposed that life had been preceded by a lengthy period of abiotic syntheses and accumulation of organic compounds that had taken place soon after the Earth was formed. Trained both as a plant biochemist and as an evolutionary biologist, Oparin found it impossible to reconcile his Darwinian credence in a gradual, slow evolution from the simple to the complex, with the commonly held suggestion that life had emerged already endowed with an autotrophic metabolism that included photosynthetic pigments, enzymes, and the ability to synthesize organic compounds from CO 2 .

Based on the simplicity and ubiquity of fermentative reactions and on a detailed analysis of chemical synthesis and astronomical observations, Oparin attempted a theoretical reconstruction of the conditions of the primitive Earth and the evolution of organic molecules into pre-cellular systems, from which anaerobic cells that nourished themselves from the soup had evolved. Some time after, the English geneticist and polymath John B. S. Haldane independently proposed a somewhat similar scheme, suggesting that a CO 2 -rich atmosphere had facilitated the formation of organic compounds, assuming that viruses represented an intermediate step in the transition from the prebiotic broth to the first cells.

Oparin and Haldane sustained their proposals in part by the striking nineteenth century laboratory syntheses of biochemical compounds achieved by Wöhler, Strecker, Butlerow, and others, but the experiments of the founders of organic chemistry were not laboratory simulations of Darwins’s warm little pond. The starting point of prebiotic chemistry is the 1953 Miller–Urey experiment, and the laboratory simulations that followed it soon led to the demonstration that many other monomers of biochemical significance could be readily synthesized under putative primitive conditions. As summarized here in the contribution by H. James Cleaves, the easiness of formation under a wide variety of conditions of amino acids, purines, and pyrimidines strongly suggests that these molecules, together with urea, carboxylic acids, sugars, aliphatic and aromatic hydrocarbons, and branched and straight fatty acids, including some which are known to form bilayered membranes, were components of the prebiotic broth.

As suggested by Juan Oró in 1961, the collisions of cometary nuclei against the primitive Earth, combined with the contribution from other extraterrestrial bodies such as meteorites and interplanetary dust, may have also spiked the primitive broth with extraterrestrial organic compounds. Regardless of their ultimate origin, simple organic compounds dissolved in the primitive oceans or other bodies of water would need to be concentrated and polymerized by simple physicochemical mechanisms.

Regardless of its ultimate sources, the organic material that may have accumulated on the early Earth before life existed very likely consisted of a wide array of different types of compounds, including many of the simple compounds that play a major role in biochemistry today. However, one must be cautious, especially when teaching to students the state of the art of prebiotic chemistry. The use of terms like “primitive soup,” “primordial broth,” or “Darwin’s warm little pond” has led in some cases to major misunderstandings, including the simplistic image of a worldwide ocean, rich in self-replicating molecules and accompanied by all sorts of biochemical monomers. The phrase “Darwin’s ‘warm little pond,’” which has long been used for convenience, refers to parts of the hydrosphere where the accumulation and interaction of the products of prebiotic synthesis may have taken place. Equally important, the fact that a number of molecular components of contemporary cells can be formed nonenzymatically in the laboratory does not necessarily means that they were also essential for the origin of life or that they were available in the prebiotic environment. It is difficult to assess the complexity of the primitive soup, which very likely included organic and inorganic chemical species spiked with metallic ions, but not all the compounds or molecular structures found today in even the simplest prokaryotes. How these abiotic organic constituents were assembled into polymers and then into the first living entities is currently one the most challenging areas of research in the study of the origin of life.

As underlined by Cleaves, the remarkable coincidence between the molecular constituents of living organisms and those synthesized in prebiotic experiments is too striking to be fortuitous, and the robustness of this type of chemistry is supported by the occurrence of most of these biochemical compounds in the 4.5-billion-year-old Murchison carbonaceous chondrite and in other carbon-rich meteorites, which are indicative of the chemistry of the primitive Solar System. How life first evolved is not known, but analysis of carbonaceous chondrites and the laboratory simulations of the primitive Earth suggest that prior to the emergence of the first living systems, the prebiotic environment was endowed with: (a) a large suite of organic compounds of biochemical significance; (b) a wide array organic and inorganic catalysts, including cyanamide and other HCN derivatives, metallic ions, sulfur-rich minerals, and clays; (c) purines and pyrimidines, i.e., the potential for template-dependent polymerization reactions; and (d) membrane-forming compounds.

Indeed, catalysis, replication, and membranes are properties that we associate with living entities, as shown by discussion on metabolism, reproduction, and cell structure. The evidence summarized here suggests that the emergence of the first life forms required not the appearance of a single living molecule but the simultaneous coordination of many different components in a confluence of processes. As B. Vlaardingerbroek discusses in his paper on the sorites paradox, first stated by the post-Socratic Greek philosopher Eubulides of Miletus, this is the point of transition between the opposite ends of a continuous process. Addressing this issue in the classroom can provide a perspective for a proper recognition that life is the outcome of an evolutionary process constrained by the laws of physics and chemistry and can lead to the acceptance that many properties associated with living systems, such as replication, self-assemblage, or catalysis are also found in nonliving entities. Some systems may not be “half-alive,” but they can exhibit some of the properties we associate with living entities, like self-organization, replication, or Darwinian evolution.

As noted by Purifcación Lopez-Garcia and David Moreira in their article on viruses included in this issue, there is a venerable intellectual tradition based on the apparent simplicity and the replicative abilities of viruses that links them to the origin of life. However, there is no evidence that viruses are indeed primitive. Such hypothesis keep resurfacing from time to time, including recent proposals that the earliest cells were preceded by stages of evolution involving virus-like genetic polymers of abiotic origin synthesized within iron-sulfide mineral compartments in warm hydrothermal environments, which are assumed to be ancestral to extant RNA viruses, retroviruses, and later on DNA viruses.

It is of course possible that (some) RNA viral genomes (or parts of them) originated during the RNA/protein world that preceded the evolutionary development of DNA biosynthesis and the divergence of the three major cell lineages addressed by Arturo Becerra and Luis Delaye in this issue. However, the proposal that such stages took place within the boundaries of hydrothermal systems is not supported by current descriptions of the primitive environment and begs major chemical issues associated with the abiotic synthesis, accumulation, and stability of ribonucleotides and polyribonucleotides.

The surprising ability of RNA molecules to catalyze an increasingly large number of chemical reactions has lent strong support to the possibility of the so-called RNA world, and as discussed here with surprising clarity by Andrew Ellington, greatly simplifies the understanding of the origin of protein biosynthesis and of the genetic code. The RNA world hypothesis, however, does not imply that life should be stripped of its identity and reduced to a mere collection of autocatalytic RNA molecules. There are many definitions of the RNA world, but they do not imply that ribozymes suddenly appeared on the primitive Earth endowed with the miraculous ability to construct a fully functional living being.

The chemical instability of RNA and the problems associated with the abiotic synthesis of its monomers have led some to suggest that RNA itself may have been preceded by simpler genetic polymers, whose appearance marked the beginning of true heredity and hence of natural selection. Not all agree with this possibility, but in any case, at the time being, the hiatus between the primitive soup and the RNA world is discouragingly enormous.

The stunning widening of the catalytic repertoire of RNA under in vitro conditions that allow the evolution of new chemical abilities to appear under selection pressures and to catalyze an increasingly large number of reactions has lent strong support to the possibility of the RNA world. Unfortunately, it is not possible to assign a precise chronology to its emergence or to other events that may have preceded extant DNA/RNA/proteins cells. The recognition that life is a very ancient phenomenon runs parallel to the limits imposed by a scarce Archaean geological record that becomes increasingly blurred as we go back in time, with very few rocks older than 3.5 billion years old.

As argued by Becerra and Delaye, a comparative genomics provides important clues on very early stages of biological evolution, which can be easily implemented in the classroom. It is true that the applicability of this approach cannot be extended beyond a threshold that corresponds to a period of cellular evolution in which ribosome-mediated protein synthesis was already in operation, but as argued by Renato Fani, bioinformatics tools, combined with a huge amount of information on classical microbial genetics, allow significant insights into the origin and early evolution of metabolic pathways. Unfortunately, it is neither possible to assign a precise chronology to the origin and earliest evolution of cells nor can we obtain direct evidence on older stages, which may have included ribozyme-mediated biosynthetic pathways.

It is unlikely that the paleontological record will provide direct data on how life first appeared and evolved. There is neither geological evidence of the environmental conditions on the Earth at the time of the origin of life nor any fossil register of the evolutionary processes that preceded the appearance of the first cells. Direct information is lacking not only on the composition of the terrestrial atmosphere during the period of the origin of life but also on the temperature, ocean pH values, and other general and local environmental conditions which may or may not have been important for the emergence of life. The attributes of the first living organisms are also unknown. They were not like extant microbes, but probably simpler than any cell now alive, and may have lacked not only protein-based catalysis, but also perhaps even the familiar genetic macromolecules, with their ribose-phosphate backbones.

The study of the origin of life is a legitimate scientific question and an alluring intellectual endeavor. Those studying it know they have plenty to be modest about, and they tend to be. We will never know in full detail how life first appeared. If this sounds pessimistic, it is; there are, after all, many gaps in the papers included in this issue of Evolution: Education and Outreach. However, we do not need, as argued by the highly vocal creationist movements that have reappeared in the U.S. and are expanding to other countries, to introduce supernatural explanations based on so-called intelligent design. The study of the origin of life has been transformed from a purely speculative discussion into a workable research program. It is true that it is ridden with controversies, but such disagreements are recognized by the scientific community as intellectual challenges and have in most cases led to fruitful clarifying debates. Evidence of scientific ignorance is not evidence for creation. There are manifold historical records that allow us to reconstruct, with different degrees of precision, the evolutionary processes that preceded the emergence of life, and the mere fact that we can address this problem is, in itself, a major intellectual achievement that can be conveyed to students and teacher alike.

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Teaching About Evolution and the Nature of Science (1998)

Chapter: chapter 5: frequently asked questions about evolution and the nature of science, 5 frequently asked questions about evolution and the nature of science.

Teachers often face difficult questions about evolution, many from parents and others who object to evolution being taught. Science has good answers to these questions, answers that draw on the evidence supporting evolution and on the nature of science. This chapter presents short answers to some of the most commonly asked questions.

Definitions

What is evolution?

Evolution in the broadest sense explains that what we see today is different from what existed in the past. Galaxies, stars, the solar system, and earth have changed through time, and so has life on earth.

Biological evolution concerns changes in living things during the history of life on earth. It explains that living things share common ancestors. Over time, evolutionary change gives rise to new species. Darwin called this process "descent with modification," and it remains a good definition of biological evolution today.

What is "creation science"?

The ideas of "creation science" derive from the conviction that God created the universe—including humans and other living things—all at once in the relatively recent past. However, scientists from many fields have examined these ideas and have found them to be scientifically insupportable. For example, evidence for a very young earth is incompatible with many different methods of establishing the age of rocks. Furthermore, because the basic proposals of creation science are not subject to test and verification, these ideas do not meet the criteria for science. Indeed, U.S. courts have ruled that ideas of creation science are religious views and cannot be taught when evolution is taught.

The Supporting Evidence

How can evolution be scientific when no one was there to see it happen?

This question reflects a narrow view of how science works. Things in science can be studied even if they cannot be directly observed or experimented on. Archaeologists study past cultures by examining the artifacts those cultures left behind. Geologists can describe past changes in sea level by studying the marks ocean waves left on rocks. Paleontologists study the fossilized remains of organisms that lived long ago.

Something that happened in the past is thus not "off limits" for scientific study. Hypotheses can be made about such phenomena, and these hypotheses can be tested and can lead to solid conclusions. Furthermore, many key aspects of evolution occur in relatively short periods that can be observed directly—such as the evolution in bacteria of resistance to antibiotics.

Isn't evolution just an inference?

No one saw the evolution of one-toed horses from three-toed horses, but that does not mean that we cannot be confident that horses evolved. Science is practiced in many ways besides direct observation and experimentation. Much scientific discovery is done through indirect experimentation

and observation in which inferences are made, and hypotheses generated from those inferences are tested.

For instance, particle physicists cannot directly observe subatomic particles because the particles are too small. They must make inferences about the weight, speed, and other properties of the particles based on other observations. A logical hypothesis might be something like this: If the weight of this particle is Y , when I bombard it, X will happen. If X does not happen, then the hypothesis is disproved. Thus, we can learn about the natural world even if we cannot directly observe a phenomenon—and that is true about the past, too.

In historical sciences like astronomy, geology, evolutionary biology, and archaeology, logical inferences are made and then tested against data. Sometimes the test cannot be made until new data are available, but a great deal has been done to help us understand the past. For example, scorpionflies ( Mecoptera ) and true flies ( Diptera ) have enough similarities that entomologists consider them to be closely related. Scorpionflies have four wings of about the same size, and true flies have a large front pair of wings but the back pair is replaced by small club-shaped structures. If Diptera evolved from Mecoptera , as comparative anatomy suggests, scientists predicted that a fossil fly with four wings might be found—and in 1976 this is exactly what was discovered. Furthermore, geneticists have found that the number of wings in flies can be changed through mutations in a single gene.

Evolution is a well-supported theory drawn from a variety of sources of data, including observations about the fossil record, genetic information, the distribution of plants and animals, and the similarities across species of anatomy and development. Scientists have inferred that descent with modification offers the best scientific explanation for these observations.

Is evolution a fact or a theory?

The theory of evolution explains how life on earth has changed. In scientific terms, "theory" does not mean "guess" or "hunch'' as it does in everyday usage. Scientific theories are explanations of natural phenomena built up logically from testable observations and hypotheses. Biological evolution is the best scientific explanation we have for the enormous range of observations about the living world.

Scientists most often use the word "fact" to describe an observation. But scientists can also use fact to mean something that has been tested or observed so many times that there is no longer a compelling reason to keep testing or looking for examples. The occurrence of evolution in this sense is a fact. Scientists no longer question whether descent with modification occurred because the evidence supporting the idea is so strong.

Why isn't evolution called a law?

Laws are generalizations that describe phenomena, whereas theories explain phenomena. For example, the laws of thermodynamics describe what will happen under certain circumstances; thermodynamics theories explain why these events occur.

Laws, like facts and theories, can change with better data. But theories do not develop into laws with the accumulation of evidence. Rather, theories are the goal of science.

Don't many famous scientists reject evolution?

No. The scientific consensus around evolution is overwhelming. Those opposed to the teaching of evolution sometimes use quotations from prominent scientists out of context to claim that scientists do not support evolution. However, examination of the quotations reveals that the scientists are actually disputing some aspect of how evolution occurs, not whether evolution occurred. For example, the biologist Stephen Jay Gould once wrote that "the extreme rarity of transitional forms in the fossil record persists as the trade secret of paleontology." But Gould, an accomplished paleontologist and eloquent educator about evolution, was arguing about how evolution takes place. He was discussing whether the rate of change of species is constant and gradual or whether it takes place in bursts after long periods when little change occurs—an idea known as punctuated equilibrium. As Gould writes in response, "This quotation, although accurate as a partial citation, is dishonest in leaving out the following explanatory material showing my true purpose—to discuss rates of evolutionary change, not to deny the fact of evolution itself."

Gould defines punctuated equilibrium as follows:

Punctuated equilibrium is neither a creationist idea nor even a non-Darwinian evolutionary theory about sudden change that produces a new species all at once in a single generation. Punctuated equilibrium accepts the conventional idea that new species form over hundreds or thousands of generations and through an extensive series of intermediate stages. But geological time is so long that even a few thousand years may appear as a mere "moment" relative to the several million years of existence for most species. Thus, rates of evolution vary enormously and new species may appear to arise "suddenly" in geological time, even though the time involved would seem long, and the change very slow, when compared to a human lifetime.

Isn't the fossil record full of gaps?

Though significant gaps existed in the fossil record in the 19th century, many have been filled in. In addition, the consistent pattern of ancient to modern species found in the fossil record is strong evidence for evolution. The plants and animals living today are not like the plants and animals of the remote past. For example, dinosaurs were extinct long before humans walked the earth. We know this because no human remains have ever been found in rocks dated to the dinosaur era.

Some changes in populations might occur too rapidly to leave many transitional fossils. Also, many organisms were very unlikely to leave fossils, either because of their habitats or because they had no body parts that could easily be fossilized. However, in many cases, such as between primitive fish and amphibians, amphibians and reptiles, reptiles and mammals, and reptiles and birds, there are excellent transitional fossils.

Can evolution account for new species?

One argument sometimes made by supporters of "creation science" is that natural selection can produce minor changes within species, such as changes in color or beak size, but cannot generate new species from pre-existing species. However, evolutionary biologists have documented many cases in which new species have appeared in recent years (some of these cases are discussed in Chapter 2 ). Among most plants and animals, speciation is an extended process, and a single human observer can witness only a part of this process. Yet these observations of evolution at work provide powerful confirmation that evolution forms new species.

If humans evolved from apes, why are there still apes?

Humans did not evolve from modern apes, but humans and modern apes shared a common ancestor, a species that no longer exists. Because we shared a recent common ancestor with chimpanzees and gorillas, we have many anatomical, genetic, biochemical, and even behavioral similarities with the African great apes. We are less similar to the Asian apes—orangutans and gibbons—and even less similar to monkeys, because we shared common ancestors with these groups in the more distant past.

Evolution is a branching or splitting process in which populations split off from one another and gradually become different. As the two groups become isolated from each other, they stop sharing genes, and eventually genetic differences increase until members of the groups can no longer interbreed. At this point, they have become separate species. Through time, these two species might give rise to new species, and so on through millennia.

Doesn't the sudden appearance of all the "modern groups" of animals during the Cambrian explosion prove creationism?

During the Cambrian explosion, primitive representatives of the major phyla of invertebrate animals appeared—hard-shelled organisms like mollusks and arthropods. More modern representatives of these invertebrates appeared gradually through the Cambrian and the Ordovician periods. "Modern groups" like terrestrial vertebrates and flowering plants were not present. It is not true that "all the modern groups of animals" appeared during this period.

Also, Cambrian fossils did not appear spontaneously. They had ancestors in the Precambrian period, but because these Precambrian forms were soft-bodied, they left fewer fossils. A characteristic of the Cambrian fossils is the evolution of hard

body parts, which greatly improved the chance of fossilization. And even without fossils, we can infer relationships among organisms from biochemical information.

Religious Issues

Can a person believe in God and still accept evolution?

Many do. Most religions of the world do not have any direct conflict with the idea of evolution. Within the Judeo-Christian religions, many people believe that God works through the process of evolution. That is, God has created both a world that is ever-changing and a mechanism through which creatures can adapt to environmental change over time.

At the root of the apparent conflict between some religions and evolution is a misunderstanding of the critical difference between religious and scientific ways of knowing. Religions and science answer different questions about the world. Whether there is a purpose to the universe or a purpose for human existence are not questions for science. Religious and scientific ways of knowing have played, and will continue to play, significant roles in human history.

No one way of knowing can provide all of the answers to the questions that humans ask. Consequently, many people, including many scientists, hold strong religious beliefs and simultaneously accept the occurrence of evolution.

Aren't scientific beliefs based on faith as well?

Usually "faith" refers to beliefs that are accepted without empirical evidence. Most religions have tenets of faith. Science differs from religion because it is the nature of science to test and retest explanations against the natural world. Thus, scientific explanations are likely to be built on and modified with new information and new ways of looking at old information. This is quite different from most religious beliefs.

Therefore, "belief" is not really an appropriate term to use in science, because testing is such an important part of this way of knowing. If there is a component of faith to science, it is the assumption that the universe operates according to regularities—for example, that the speed of light will not change tomorrow. Even the assumption of that regularity is often tested—and thus far has held up well. This "faith" is very different from religious faith.

Science is a way of knowing about the natural world. It is limited to explaining the natural world through natural causes. Science can say nothing about the supernatural. Whether God exists or not is a question about which science is neutral.

Legal Issues

Why can't we teach creation science in my school?

The courts have ruled that "creation science" is actually a religious view. Because public schools must be religiously neutral under the U.S. Constitution, the courts have held that it is unconstitutional to present creation science as legitimate scholarship.

In particular, in a trial in which supporters of creation science testified in support of their view, a district court declared that creation science does not meet the tenets of science as scientists use the term ( McLean v. Arkansas Board of Education ). The Supreme Court has held that it is illegal to require that creation science be taught when evolution is taught ( Edwards v. Aguillard ). In addition, district courts have decided that individual teachers cannot advocate creation science on their own ( Peloza v. San Juan Capistrano School District and Webster v. New Lennox School District ).

Teachers' organizations such as the National Science Teachers Association, the National Association of Biology Teachers, the National Science Education Leadership Association, and many others also have rejected the science and pedagogy of creation science and have strongly discouraged its presentation in the public schools. (Statements from some of these organizations appear in Appendix C .) In addition, a coalition of religious and other organizations has noted in "A Joint Statement of Current Law" (see Appendix B ) that "in science class, [schools] may present only genuinely scientific critiques of, or evidence for, any explanation of life on earth, but not religious

critiques (beliefs unverifiable by scientific methodology)."

Some argue that "fairness" demands the teaching of creationism along with evolution. But a science curriculum should cover science, not the religious views of particular groups or individuals.

Educational Issues

If evolution is taught in schools, shouldn't creationism be given equal time?

Some religious groups deny that microorganisms cause disease, but the science curriculum should not therefore be altered to reflect this belief. Most people agree that students should be exposed to the best possible scholarship in each field. That scholarship is evaluated by professionals and educators in those fields. In science, scientists as well as educators have concluded that evolution—and only evolution—should be taught in science classes because it is the only scientific explanation for why the universe is the way it is today.

Many people say that they want their children to be exposed to creationism in school, but there are thousands of different ideas about creation among the world's people. Comparative religions might comprise a worthwhile field of study but not one appropriate for a science class. Furthermore, the U.S. Constitution states that schools must be religiously neutral, so legally a teacher could not present any particular creationist view as being more "true" than others.

Why should teachers teach evolution when they already have so many things to teach and can cover biology without mentioning evolution?

Teachers face difficult choices in deciding what to teach in their limited time, but some ideas are of central importance in each discipline. In biology, evolution is such an idea. Biology is sometimes taught as a list of facts, but if evolution is introduced early in a class and in an uncomplicated manner, it can tie many disparate facts together. Most important, it offers a way to understand the astonishing complexity, diversity, and activity of the modern world. Why are there so many different types of organisms? What is the response of a species or community to a changing environment? Why is it so difficult to develop antibiotics and insecticides that are useful for more than a decade or two? All of these questions are easily discussed in terms of evolution but are difficult to answer otherwise.

A lack of instruction about evolution also can hamper students when they need that information to take other classes, apply for college or medical school, or make decisions that require a knowledge of evolution.

Should students be given lower grades for not believing in evolution?

No. Children's personal views should have no effect on their grades. Students are not under a compulsion to accept evolution. A grade reflects a teacher's assessment of a student's understanding. If a child does not understand the basic ideas of evolution, a grade could and should reflect that lack of understanding, because it is quite possible to comprehend things that are not believed.

Can evolution be taught in an inquiry-based fashion?

Any science topic can be taught in an inquiry-oriented manner, and evolution is particularly amenable to this approach. At the core of inquiry-oriented instruction is the provision for students to collect data (or be given data when collection is not possible) and to analyze the data to derive patterns, conclusions, and hypotheses, rather than just learning facts. Students can use many data sets from evolution (such as diagrams of anatomical differences in organisms) to derive patterns or draw connections between morphological forms and environmental conditions. They then can use their data sets to test their hypotheses.

Students also can collect data in real time. For example, they can complete extended projects involving crossbreeding of fruit flies or plants to illustrate the genetic patterns of inheritance and the influence of the environment on survival. In this way, students can develop an understanding of evolution, scientific inquiry, and the nature of science.

Today many school students are shielded from one of the most important concepts in modern science: evolution. In engaging and conversational style, Teaching About Evolution and the Nature of Science provides a well-structured framework for understanding and teaching evolution.

Written for teachers, parents, and community officials as well as scientists and educators, this book describes how evolution reveals both the great diversity and similarity among the Earth's organisms; it explores how scientists approach the question of evolution; and it illustrates the nature of science as a way of knowing about the natural world. In addition, the book provides answers to frequently asked questions to help readers understand many of the issues and misconceptions about evolution.

The book includes sample activities for teaching about evolution and the nature of science. For example, the book includes activities that investigate fossil footprints and population growth that teachers of science can use to introduce principles of evolution. Background information, materials, and step-by-step presentations are provided for each activity. In addition, this volume:

• Presents the evidence for evolution, including how evolution can be observed today.
• Explains the nature of science through a variety of examples.
• Describes how science differs from other human endeavors and why evolution is one of the best avenues for helping students understand this distinction.
• Answers frequently asked questions about evolution.

Teaching About Evolution and the Nature of Science builds on the 1996 National Science Education Standards released by the National Research Council—and offers detailed guidance on how to evaluate and choose instructional materials that support the standards.

Comprehensive and practical, this book brings one of today's educational challenges into focus in a balanced and reasoned discussion. It will be of special interest to teachers of science, school administrators, and interested members of the community.

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Defining life and evolution: Essay on the origin, expansion, and evolution of living matter

Affiliation.

• 1 Institute of Molecular Biology and Genetics of the National Academy of Sciences of Ukraine, Kyiv, 03143, Ukraine. Electronic address: [email protected].
• PMID: 34352326
• DOI: 10.1016/j.biosystems.2021.104500

This essay aims to define the origin, expansion, and evolution of living matter. The first formations, identified as remains, fossils, traces etc. of life are almost as old as the Earth itself. During four billion years, life on the Earth has continuously existed and been implemented in the range of conditions, ensuring the liquid state of water. During the entire period of life existence, its evolution was proceeding with the tendency of multidirectionality, after each catastrophe tending to the diversity and vastness of distribution, and all the currently living species, regardless of their complexity, have the same evolutionary age. The property of reproductive surplus (multiplication) is inherent in all the living matter. The reproduction of all the living matter is implemented via the "development" - a process of continuous occurrence of something new that did not exist in the previous moment in the reproduced individual at each specific moment of time with the tendency towards the reproduction of a "copy". In its fundamental basis, Life is based on a programme, its material support is implemented and exists not in the field of causative-consecutive events, but in the field of programmed-causative-consecutive events. This predetermines the "biology laws", the behaviour of the material constituent of Life at each time period, and the future of the material constituent of life.

Keywords: Development; Evolution; Genetic program; Origin of life; biological Complexity.

Copyright © 2021 Elsevier B.V. All rights reserved.

• Biological Evolution*
• Biology / methods
• Earth, Planet
• Evolution, Chemical*
• Extraterrestrial Environment
• Models, Biological
• Origin of Life*
• Reproduction / physiology
• Time Factors

• Theories of Origin and Evolution of Life

There are many views on how life originated on earth . The earth is said to have come into existence 5 billion years ago and life on earth came into existence only a billion years after that. There were many scientists who studied the fossils and performed experiments to postulate their versions of the theory of evolution .

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Theories of origin of life.

In olden days, people believed that the universe and life on it was an act and result of God’s creation. There was, however, no evidence to support these claims.The early scientists and Greeks believed that life on earth never began on earth itself. They believed that it came from somewhere else in outer space and they named this phenomenon ‘panspermia’.

Then came the theory of spontaneous generation of life during the times of Aristotle who believed that life was born from decaying and rotting inorganic matter such as hay, straw, and other non- living material . This theory was rubbished by Louis Pasteur.

Next came the ‘chemical evolution of life’ theory by two scientists- Oparin from Russia and Haldane from England. They believed that the generation of life on earth was a slow chemical process which occurred from pre-existing non-living materials such as amino acids , proteins and nuclear material such as RNA. They postulated that these organic materials came together under conditions of high temperature , reducing atmosphere(without oxygen) and gases released from volcanos all of which were favourable to produce simple living forms. So they called this mixture of organic materials as ‘organic soup’.

Browse more Topics under Evolution

• Stages of Evolution
• Evidences of Evolution

Miller Urey Experiment

Miller and Urey were two scientists who believed Oparin and Haldane and wanted to prove their theory. So, they performed the famous ‘Miller- Urey experiment’ in the lab.

(Source: bbc.co.uk)

• They replicated the environmental and atmospheric conditions that may have existed in the primitive earth in their lab by taking gases like methane, ammonia, hydrogen and water vapour in a closed vessel.
• When they came back to check the results of their experiment after a week, they detected the presence of amino acids, nitrogen bases, fats, and sugar.
• With these results, the theory of gradual chemical evolution was accepted.
• This experiment gave the other scientists to piece the remaining pieces together.

It was believed that monomeric units that formed due to chemical evolution polymerized to form polymeric units and that gave rise to the unicellular microorganisms and eventually gave rise to multicellular more complex species. This is called biogenesis.

Similar to the above-discussed theories of the origin of life, there were many theories of the evolution of life.

Theory of Evolution

There were many theories of evolution that were postulated based on the evidence but the most accepted important ones are as follows:

Lamarck’s Theory of inheritance of Acquired Characters

This theory of evolution was published in the book ‘Philosphic Zoologique’ by French scientist Jean Lamarck. His theory was based on the study of fossils of the organisms of the past with their present relatives including the homologous, analogous and vestigial organs. He believed that an organ or structure got modified in the current animal from its ancestor due to the change in the environment and the utility of that particular organ. His theory also said that the organs or structures modified themselves to suit the new needs of the organism. His theory contained three postulates:

• Acquisition of new characters, organs or structures
• Inheritance of acquired characters

Example: The giraffe originally did not have its long neck. But, the trees were very tall and it could not feed on the minimal number of short trees. So, as an adaptive measure to be able to eat leaves on the tall trees, the giraffe’s neck started growing longer. This was a way of adaptive mechanism due to new needs.

(Source: haikudeck.com)

Lamarck’s theory of evolution was disproved by scientists like Weismann and Mendel by carrying out their own experiments which were not consistent with Lamarck’s postulates.

Darwin’s Theory of Natural Selection

Charles Darwin along with Wallace postulated this theory of evolution. Darwin believed that life thrives and multiplies by the principle of natural selection. The theory of natural selection had the following postulates:

• Increased reproduction- He said that each and every organism or species tend to reproduce to the maximum to let its species live and multiply. He said that populations of all organisms multiply geometrically.
• The arithmetic growth of food and availability of space- Darwin says that though the organism and their species multiply geometrically, food multiplies only arithmetically and the space available remains a constant. With both these restrictions to the growing population of different species puts a tab on the population growth.
• Struggle- with a rapidly multiplying population, there is an increased demand for both space and food. But, due to the restricted space and slowly growing food, there arises a competition between the members of a species and between species for the food and space. The organism or species that is able to fight its own species or the other species or the environment itself lives.
• Variations- Due to this struggle for food and space, each organism or species tend to get an advantage over the other. In order to do so, they tend to develop certain features or structures that give them that added advantage to succeed in the struggle of life. So, this struggle brings about variations.
• Survival of the fittest- Darwin’s theory of natural selection thus believes that those who can survive till the end are the ones that nature selects.

Solved Example for You

Q: Who postulated the theory of chemical evolution?

• Miller and Urey
• Oparin and Haldane 
• Darwin and Wallace

Sol: The correct answer is (c) Oparin and Haldane

Oparin and Haldane believed that the life on earth came into existence from a pre-existing inorganic material such as mud, clay, hay etc. They believed a gradual conversion of these materials in the primitive environment of earth gave rise to small molecules which later on polymerized to give rise to complex molecules and organisms.

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Reason and Meaning

Philosophical reflections on life, death, and the meaning of life, evolution and the meaning of life.

IS THERE A CONNECTION BETWEEN EVOLUTION AND MEANING ?

In previous blog posts (“Death Is Bad,” and “Can Science Give Us Immortality”) we have given two reasons to believe that life is meaningful: 1)it is beneficial to be optimistic about the question; and 2) there is a possibility of technological immortality.

We now ask if the idea of evolution supports the claim that life is meaningful, or is becoming meaningful, or is becoming increasingly meaningful. Does evolution add to the case for meaning? Is there anything about evolution in general—as opposed to technological evolution specifically—which sheds light on meaning? Is there anything about evolution as a whole—cosmic, biological, and cultural—which implies that life is meaningful, or that meaning emerges, or that, given enough time, complete meaning will be attained, actualized, or approached as a limit? Does an a posteriori analysis of past evolution allow us to draw positive conclusions about the meaning of life? Perhaps there is a progressive directionality to evolution, perhaps the meaningful eschatology of the universe will gradually unfold as we evolve, and perhaps we can articulate a cosmic vision to describe this unfolding—or perhaps not.

SUMMARY OF SOME THINKERS ON THE SUBJECT

Cosmic evolution evokes the idea of evolutionary progress , as we saw earlier in thinkers like Ray Kurzweil and Hans Moravec, while progressivism imbues the work of most biologists, a trend the philosopher and historian of biology Michael Ruse thinks will continue. 1  When we turn to culture, a compelling argument can be made for the reality of progressive evolution. (A case bolstered by the theory of memetics.) Will Durant argued for cultural progress, a conclusion that follows straightforwardly from elements of human history, while Jean Piaget made the case for cognitive progress, based on his studies of cognitive development in children and his analysis of the history of science. 2 3 Robert Wright believes in a generally progressive evolution based on the structure of non-zero sum interactions, whereas Steven Pinker counters that complexity and cooperation are sub-goals of evolution, not its natural destiny. 4 5  While the overall strength of the arguments for evolutionary progress is unclear, we cannot gainsay that such arguments have philosophical merit. Clearly there have been some progressive trends in evolution, which intimates that life as a whole may become increasingly meaningful.

A number of thinkers argue for the relevance of evolution to meaning . Daniel Dennett extends the heuristic reach of evolution, showing how it acts as a universal solvent that eats through philosophical problems, while Michael Shermer says that we create provisional meanings in our lives, even though our existence depends on a billion evolutionary happenstances. 6 7  Steve Stewart-Williams argues that the universe does have purposes, since we have purposes and we are part of the universe, while John Stewart claims that the universe will be increasingly meaningful if we direct the process. 8 9  Still, other philosophers have argued that evolution is irrelevant to meaning; for example, Wittgenstein notoriously maintained that “Darwin’s theory has no more to do with philosophy than any other hypothesis in natural science.” 10  Yet this claim was made in a philosophical milieu where the scope of philosophical inquiry was narrow, whereas today the impact of scientific theories on philosophy is enormous. Today most thinkers would say that the emergence of conscious purposes and meanings in cosmic evolution is relevant to concerns about meaning.

GRAND EVOLUTIONARY VISIONS

Turning to grand cosmic visions , the French paleontologist and Jesuit Pierre Teilhard de Chardin articulated a universal vision of the evolutionary process, with the universe moving toward a fully meaningful end point. 11  The biologist Jacques Monod notably questioned Teilhard’s optimism, noting that biology reveals no meaning. 12  Biologist Julian Huxley conveyed a vision—similar to Teilhard’s but without the religious connotations—in which we are encouraged to play the leading role in the cosmic drama by guiding evolution to realize its possibilities, thereby finding meaning for ourselves in the process. 13 14 15  E. O. Wilson follows this line of thinking—the evolutionary epic is mythic and sweeping—and exhorts us to create a better future. 16  Thus many thinkers believe that evolution is both progressive and relevant to meaning; in fact it is a key that unlocks the secret of meaning. For Teilhard, Huxley, and Wilson, life is meaningful because it evolves, and we live meaningful lives precisely because we play a central role in this evolving meaning .

We will explore each of these thinkers in greater detail in our forthcoming posts.

______________________________________________________________________

 1. Michael Ruse,  Monad to Man: The Concept of Progress in Evolutionary Biology,  (Cambridge: Harvard University Press, 2009). 2. Will Durant, “Ten Steps Up From the Jungle,” The Rotarian, January 1941, 10. 3.  For more see John G. Messerly, Piaget’s Conception of Evolution (Lanham Md.: Rowman & Littlefield, 1996). 4. Robert Wright, Non-Zero: The Logic of Human Destiny (New York: Vintage, 2001), 331 5. http://www.slate.com/articles/arts/the_book_club/features/2000/nonzero/_2.html 6. Daniel Dennett, Darwin’s Dangerous Idea (New York: Simon & Schuster, 1996). 7. http://www.godlikeproductions.com/forum1/message563977/pg1 8. Steve Stewart-Williams, Darwin, God and the Meaning of Life: How Evolutionary Theory Undermines Everything You Thought You Knew (Cambridge: Cambridge University Press, 2010), 194. 9. John Stewart, “The Meaning of Life In A Developing Universe,” http://www.evolutionarymanifesto.com/meaning.pdf., 14. 10. Ludwig Wittgenstein,  Tractatus Logico-Philosophicus , trans. D.F. Pears and B.F. McGuiness (London: Routledge & Paul Kegan, 1961), 25. 11. Teilhard de Chardin, Pierre,  The Phenomenon of Man (New York: Harper Collins, 1975), 219. 12. Jacques Monod, Chance and Necessity: An Essay on the Natural Philosophy of Modern Biology (New York: Vintage, 1972), 112. 13. Julian Huxley, “The Creed of a Scientific Humanist” in The Meaning of Life , ed. E.D. Klemke (Oxford: Oxford University Press 2000, 81. 14. Julian Huxley, Religion without Revelation , (London: Max Parrish, 1959), 236. 15. Julian Huxley, New Bottles for New Wine (New York: Harper & Brothers, 1957), 13-16.  Edward O. Wilson, On Human Nature (Cambridge: Harvard University Press, 1979) 169.

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Everyday life and its variability influenced human evolution at least as much as rare activities like big-game  hunting

Professor and Chair of Biology at Seattle Pacific University and Affiliate Assistant Professor of Anthropology, University of Washington

Disclosure statement

Cara Wall-Scheffler does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

University of Washington provides funding as a member of The Conversation US.

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Think about taking a walk: where you need to go, how fast you need to move to get there, and whether you need to bring something along to carry the results of your errand.

Are you going on this walk with someone else? Does walking with a friend change your preparation? If you’re walking with a child, do you remember to bring an extra sweater or a snack? You probably did – because people intuitively vary their plan depending on their current needs and situations.

In my research as an anthropologist , I’ve focused on the evolution of human walking and running because I love the flexibility people bring to these behaviors. Humans in all kinds of environments across space and time vary how far they go, when they go and what they go for – whether food, water or friends – based on a multitude of factors, including season, daylight, rituals and family.

Anthropologists split their studies of human activity into two broad categories: what people need to do – including eat, keep their kids alive and so on – and what solutions they come up with to accomplish these needs.

How people keep their children alive is a key issue in my research because it has a direct impact on whether a population survives. It turns out that kids stay alive if they’re with adults. To this end, it is a human universal that women carry heavy loads every day , including kids and their food. This needs-based behavior seems to have been an important part of our evolutionary history and explains quite a few aspects of human physiology and female morphology , such as women’s lower center of mass .

The solutions to other key problems, like specifically which food women will be carrying, vary across time and space. I suggest that these variations are as integral to explaining human biology and culture as the needs themselves.

Impacts of uncommon activities

Evolutionary scientists often focus on how beneficial heritable traits get passed on to offspring when they provide a survival advantage. Eventually a trait can become more common in a population when it provides a useful solution.

For example, researchers have made big claims about how influential persistence hunting via endurance running has been on the way the human body evolved. This theory suggests that taking down prey by running them to exhaustion has led to humans’ own abilities to run long distances – by increasing humans’ ability to sweat, strengthening our head support and making sure our lower limbs are light and elastic.

But persistence hunting occurs in fewer than 2% of the recorded instances of hunting in one major ethnographic database , making it an extremely rare solution to the need to find food. Could such a rare and unusual form of locomotion have had a strong enough impact to select for the suite of adaptive traits that make humans such excellent endurance athletes today?

Maybe persistence hunting is actually a fallback strategy, providing a solution only at key moments when survivorship is on the edge. Or maybe these capabilities are just side effects of the loaded walking done every day . I think a better argument is that the ability to predict how to move between common and uncommon strategies has been the driver of human endurance capacity.

Everyday life’s influence on evolution

Hunting itself, especially of large mammals, is hardly ubiquitous , despite how frequently it is discussed. For example, anthropologists tend to generalize that people who lived in the Arctic even up to a hundred years ago consumed only animal meat hunted by men. But actually, the original ethnographic work reveals a far more nuanced picture .

Women and children were actively involved in hunting, and it was a strongly seasonal activity. Coastal fishing, berry picking and the use of plant materials were all vital to Arctic people’s day-to-day sustenance. Small family groups used canoes for coastal foraging for part of the year.

During other seasons, the whole community participated in hunting large mammals by herding them into dangerous situations where they were more easily killed. Sometimes family groups were together, and sometimes large communities were together. Sometimes women hunted with rifles, and sometimes children ran after caribou.

The dynamic nature of daily life means that the relatively uncommon activity of hunting large terrestrial vertebrates is unlikely to be the main behavior that helps humans solve the key problems of food, water and keeping children alive.

Anthropologist Rebecca Bliege Bird has investigated how predictable food is throughout the day and the year . She’s noted that for most communities, big game is rarely caught, especially when a person is hunting alone. Even among the Hadza in Tanzania, generally considered a big-game hunting community, a hunter acquires 0.03 prey per day on average – essentially 11 animals a year for that person.

Bird and others clearly argue that the planning and flexible coordination done by females is the crucial aspect of how humans survive on a daily basis. It’s the daily efforts of females that allow people to be spontaneous a few times a year to accomplish high-risk activities such as hunting – persistence or otherwise. Therefore it is female flexibility that allows communities to survive between the rare big-game opportunities.

Changing roles and contributions

Some anthropologists argue that in some parts of the world, behavior varies more for cultural reasons , like what tools you make, than for environmental ones, such as how much daylight there is during winter. The importance of culture means that the solutions vary more than the needs.

One of the aspects of culture that varies is the role assigned to specific genders. Varying gender roles are related to the distribution of labor and when people take on certain solution-based tasks . In most cultures, these roles change across a female’s life span. In American culture, this would be like a grandparent going back to college to hone a childhood passion in order to take on a new job to send their grandchildren to college.

In many places, females go from youth when they might carry their siblings and firewood, to early parenthood where they might go hunting with a baby on their back , to older parenthood where they might carry water on their head, a baby on their back and tools in their hands, to postmenopausal periods when they might carry giant loads of mangoes and firewood to and from camp.

Even though always load carrying , our capacity to plan and change our behavior for diverse environments is part of what drives Homo sapiens ’ success, which means that the behavior of females across their different life stages has been a major driver of this capability.

• Anthropology
• Human evolution
• Ethnography
• Women's bodies

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Human evolution: short essay on human evolution.

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Man is a product of evolution. Therefore human evolution is intimately related to the origin of life and its development on the face of earth. It is customary to speak of evolution ‘from amoeba to Man’, as if the amoeba is the simplest form of life. But in reality, there are several organisms more primitives than amoeba, say for example viruses. The evolution from a self-replicating organic molecule to a protozoan, like amoeba, is the most complex step in evolution, which might have consumed the same extent of time from protozoan to man.

The term evolution was first applied by the English philosopher Herbert Spencer to mean the historical development of life. Since then evolution denotes a change, although the term may be defined in several ways. In the context of man, the biological evolution started with the ‘Origin of life’. In the beginning, there was nothing. The first successful formation of protoplasm initiated the life and its continuous development proceeded towards complexity to give rise different life forms of evolved type.

About 10 billion years after the formation of Universe, the earth was formed. Life on earth appeared far late, nearly three billion years ago. Of the several evolutionary problems, perhaps the origin of life is the most critical, since there is no record concerning it. Life has been characterized by the capacity of performing certain vital functional activities like metabolism, growth and reproduction. There is no ambiguity regarding this point. But how the first life came on earth is a matter of conjecture.

Ancient thinkers speculated that life originated spontaneously from inorganic components of the environment, just after the formation of earth. A series of physio-chemical processes were perhaps responsible behind this creation. Aristotle (384 BC to 322 BC) was the pioneer in this line of thought and nobody raised any voice against his speculation till seventeenth Century. But in seventeenth Century, an Italian scientist, Francesco Redi (1627 -1697) made an experiment with two pieces of meat.

One of the pieces was kept fully covered and the other piece was kept in an open place. After some days he examined both of the pieces very carefully. He noticed that, flies laid eggs on the uncovered piece of meat and so many new flies had born. But the covered piece of meat had not produced any new fly, as there was absolutely no access of flies.

Redi tried to establish the fact, that living organisms cannot be originated spontaneously from inorganic components. More or less at the same time, Leuwenhock (1632 – 1723) by studying several microorganisms like protozoa, sperm, bacteria etc. under microscope declared that the spontaneous generation was possible for the microorganisms. Later, Louis Pasteur (1822 -1895) also studied much to furnish evidences in support of spontaneous creation.

In fact, scientists of this period were perplexed in finding out how life began spontaneously as a matter of chance. Philosophers, Thinkers and Scientists all had submitted their varied thought and propositions regarding the nature and mechanism of origin of life on earth. Different religions had also put forth different concepts in this connection.

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