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Charles Darwin's theory of evolution by natural selection made us rethink our place in the world. The idea that humans shared a common ancestor with apes was a challenge to the foundations of western civilisation.
Darwin kept silent for 20 years before going public and was only half joking when he described writing his book 'On the Origin of Species' as 'like confessing a murder'. This is the story of one man's struggle with the most radical idea of all time.

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Charles Darwin: Evolution and the story of our species

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Charles Darwin's theory of evolution by natural selection made us rethink our place in the world. The idea that humans shared a common ancestor with apes was a challenge to the foundations of western civilisation. Darwin kept silent for 20 years before going public and was only half joking when he described writing his book 'On the Origin of Species' as 'like confessing a murder'.

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Answer the quizz with the following documents

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docx

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What is evolution and how does it work? Evolution 101 provides the nuts-and-bolts on the patterns and mechanisms of evolution. You can explore the following sections: An introduction to evolution Evolution briefly defined and explained The history of life: looking at the patterns How does evolution lead to the tree of life?

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part1

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pdf

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3-work sheet on Darwin's impact on the Theory of evolution

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3-work sheet on Darwin's impact on the Theory of evolution

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Descent with modification

We've defined evolution as descent with modification from a common ancestor, but exactly what has been modified? Evolution only occurs when there is a change in gene frequency within a population over time. These genetic differences are heritable and can be passed on to the next generation — which is what really matters in evolution: long term change.

Compare these two examples of change in beetle populations. Which one is an example of evolution?

1. Beetles on a diet
Imagine a year or two of drought in which there are few plants that these beetles can eat.

All the beetles have the same chances of survival and reproduction, but because of food restrictions, the beetles in the population are a little smaller than the preceding generation of beetles.

2. Beetles of a different color
Most of the beetles in the population (say 90%) have the genes for bright green coloration and a few of them (10%) have a gene that makes them more brown.

Some number of generations later, things have changed: brown beetles are more common than they used to be and make up 70% of the population.

Which example illustrates descent with modification — a change in gene frequency over time?

The difference in weight in example 1 came about because of environmental influences — the low food supply — not because of a change in the frequency of genes. Therefore, example 1 is not evolution. Because the small body size in this population was not genetically determined, this generation of small-bodied beetles will produce beetles that will grow to normal size if they have a normal food supply.

The changing color in example 2 is definitely evolution: these two generations of the same population are genetically different. But how did it happen?

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Descent with modification We've defined evolution as descent with modification from a common ancestor, but exactly what has been modified? Evolution only occurs when there is a change in gene frequency within a population over time. These genetic differences are heritable and can be passed on to the next generation - which is what really matters in evolution: long term change.

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part 2

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Look at the 5 videos.

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Darwin part en voyage durant cinq ans où il passera la majorité de son temps à terre. Ses observations vont révolutionn...

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The acceptance of biological evolution is an essential part of the modern scientific explanation of the natural world. Most scientists and major religions in the Western World have long since incorporated it into their understanding of nature and humanity. However, some churches still maintain that there was a special and independent creation of every species and that life forms do not change through time from generation to generation. These "creationists" often share beliefs about the Judeo-Christian Bible that were widely held, even by scientists, during the early 19th century and before.

James Ussher
1581-1656

The traditional Judeo-Christian version of creationism was strongly reinforced by James Ussher , a 17th century Anglican archbishop of Armagh in Northern Ireland. By counting the generations of the Bible and adding them to modern history, he fixed the date of creation at October 23, 4004 B.C. During Ussher's lifetime, debate focused only on the details of his calculations rather than on the approach. Dr. Charles Lightfoot of Cambridge University in England had the last word. He proclaimed that the time of creation was 9:00 A.M. on October 23, 4004 B.C.

This belief that the earth and life on it are only about 6000 years old fit neatly with the then prevalent theory of the "Great Chain of Being." This held that God created an infinite and continuous series of life forms, each one grading into the next, from simplest to most complex, and that all organisms, including humans, were created in their present form relatively recently and that they have remained unchanged since then. Given these strongly held beliefs, it is not surprising that 17th and 18th century European biology consisted mainly of the description of plants and animals as they are with virtually no attempt to explain how they got to be that way.

Carolus Linnaeus
1707-1778

The leading biological scientist of the mid 18th century was the Swedish botanist Karl von Linn ( Carolus Linnaeus in Latin). His 180 books are filled with precise descriptions of nature, but he did little analysis or interpretation. This is to be expected since Linnaeus apparently believed that he was just revealing the unchanging order of life created by God. The goal of documenting change in nature would not have made sense to him. Late in his life, however, he was troubled by the fact that plant hybrids could be created by cross pollination. These were varieties that had not existed before. Linnaeus stopped short of concluding that these plants had evolved.

Despite his limiting research bias, Linnaeus was a first class scientist. His most important contribution to science was his logical classification system for all living things which he proposed in his book Systema Naturae, first published in 1735. In this and subsequent works, he described plants and animals on the basis of physical appearance and method of reproduction. He classified them relative to each other according to the degree of their similarities. He used a binomial nomenclature in naming them. That is to say, organisms were given two Latin names--genus and species . Each genus could have many related species. Each genus was also part of larger categories of living things. This Linnaean system of classification is today the basis for naming and describing organisms in all fields of biology.

genus

genus

species

species

species

species

John Ray
1627-1705

The concept of genus and species was actually developed in the late 1600's by John Ray, an English naturalist and ordained minister. However, it was Linnaeus who used this system to name us Homo sapiens (literally, "wise men"). He also placed us in the order Primates (a larger, more inclusive category than our genus) along with all of the apes, monkeys, and prosimians. This was very controversial at the time since it implied that people were part of nature, along with other animals and plants. In addition, it meant that we were biologically closer to the other primates than to all other animals.

Comte de Buffon
1707-1788

Late in the 18th century, a small number of European scientists began to quietly suggest that life forms are not fixed. The wealthy French mathematician and naturalist, George Louis Leclerc, Comte de Buffon (1749-1804) , actually said that living things do change through time. He speculated that this was somehow a result of influences from the environment or even chance. He believed that the earth must be much older than 6000 years. In 1774, in fact, he speculated that the earth must be at least 75,000 years old. He also suggested that humans and apes are related. Buffon was careful to hide his radical views in a limited edition 44 volume natural history book series called Histoire Naturelle . By doing this, he avoided broad public criticism.

Buffon was an early advocate of the Linnaean classification system. He was also a quiet pioneer in asserting that species can change over generations. However, he publicly rejected the idea that species could evolve into other species. One of his most significant contributions to the biological sciences was his insistence that natural phenomena must be explained by natural laws rather than theological doctrine.

Erasmus Darwin
1731-1802

Another late 18th century closet-evolutionist was Erasmus Darwin Zoonomia; or, the Laws of Organic Life , the grandfather of the well known 19th century naturalist, Charles Darwin. Erasmus was an English country physician, poet, and amateur scientist. He believed that evolution has occurred in living things, including humans, but he only had rather fuzzy ideas about what might be responsible for this change. He wrote of his ideas about evolution in poems and a relatively obscure two volume scientific publication entitled (1794-1796). In this latter work, he also suggested that the earth and life on it must have been evolving for "millions of ages before the commencement of the history of mankind."

The first evolutionist who confidently and very publicly stated his ideas about the processes leading to biological change was a French protg of the Comte de Buffon. He was Jean-Baptiste Chevalier de Lamarck . Unfortunately, his theory about these processes was incorrect.

Lamarck believed that microscopic organisms appear spontaneously from inanimate materials and then transmute, or evolve, gradually and progressively into more complex forms through a constant striving for perfection. The ultimate product of this goal-oriented evolution was thought by Lamarck to be humans. He believed that evolution was mostly due to the inheritance of acquired characteristics as creatures adapted to their environments. That is, he believed that evolution occurs when an organism uses a body part in such a way that it is altered during its lifetime and this change is then inherited by its offspring. For example, Lamarck thought that giraffes evolved their long necks by each generation stretching further to get leaves in trees and that this change in body shape was then inherited. Likewise, he believed that wading birds, such as herons and egrets, evolved their long legs by stretching them to remain dry. Lamarck also believed that creatures could develop new organs or change the structure and function of old ones as a result of their use or disuse.

Lamarck did not invent the idea of inheritance of acquired characteristics but stated it clearly and publicly in an 1809 publication entitled It was relatively easy for the French scientist, Philosophie Zoologique. George Cuvier , and other critics of Lamarck to discredit his theory. If it was correct, the children of cowboys who have developed bowed legs as a result of a lifetime of riding horses would be born with bowed legs as well. That, of course, does not occur. Likewise, the children of professional weight lifters are not born with enlarged muscles.

George Cuvier
1769-1832

While Lamarck's explanation of evolution was incorrect, it is unfair to label him a bad scientist. In fact, he was at the cutting edge of biological research for his time. He and George Cuvier were largely responsible for making biology a distinct branch of science.

Despite his criticism of Lamarck, Cuvier did not reject the idea that there had been earlier life forms. In fact, he was the first scientist to document extinctions of ancient animals and was an internationally respected expert on dinosaurs. However, he rejected the idea that their existence implied that evolution had occurred--he dogmatically maintained the "fixity" of species.

Cuvier advocated the theory of catastrophism , as did most other leading scientists of his day. This held that there have been violent and sudden natural catastrophes such as great floods and the rapid formation of major mountain chains. Plants and animals living in those parts of the world where such events occurred were often killed off according to Cuvier. Then new life forms moved in from other areas. As a result, the fossil record for a region shows abrupt changes in species. Cuvier's explanation relied solely on scientific evidence rather than biblical interpretation.

Charles Lyell
1797-1875

A careful examination of European geological deposits in the early 19th century led the English lawyer and geologist, Charles Lyell , to conclude that Cuvier's catastrophism theory was wrong. He believed that there primarily have been slower, progressive changes. In his three volume Principles of Geology (1830-1833), Lyell documented the fact that the earth must be very old and that it has been subject to the same sort of natural processes in the past that operate today in shaping the land. These forces include erosion, earthquakes, glacial movements, volcanoes, and even the decomposition of plants and animals.

James Hutton
1726-1797

Lyell provided conclusive evidence for the theory of uniformitarianism , which had been developed originally by the late 18th century Scottish geologist, James Hutton. This held that the natural forces now changing the shape of the earth's surface have been operating in the past much the same way. In other words, the present is the key to understanding the past.

This revolutionary idea was instrumental in leading Charles Darwin to his understanding of biological evolution in the 1830's. However, it was not until the late 19th century that most educated people in the Western world finally rejected the theory of catastrophism in favor of uniformitarianism.

Today, we know that our planet has been shaped by occasional catastrophic events, such as bombardment of large meteors, in addition to the comparatively slower natural processes suggested by uniformitarianism. All of these events have potentially affected the rate and direction of biological evolution.
NOTE : While George Cuvier and Charles Lyell strongly disagreed about how the earth got to be the way it is today, they both rejected the idea of biological evolution. However, neither man accepted a traditional Biblical account of creation and a young earth. Cuvier did not live long enough to learn about Charles Darwin's proof of evolution, but Lyell did. He came to accept this proof in the early 1860's along with most leading scientists of that time. Lyell also became a friend of Charles Darwin.

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Early Theories of Evolution: Pre-Darwinian Theories

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The acceptance of biological evolution is an essential part of the modern scientific explanation of the natural world. Most scientists and major religions in the Western World have long since incorporated it into their understanding of nature and humanity.

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Mechanisms of change

Each of these four processes is a basic mechanism of evolutionary change.

Mutation
A mutation could cause parents with genes for bright green coloration to have offspring with a gene for brown coloration. That would make genes for brown coloration more frequent in the population than they were before the mutation.

Migration
Some individuals from a population of brown beetles might have joined a population of green beetles. That would make genes for brown coloration more frequent in the green beetle population than they were before the brown beetles migrated into it.

Genetic drift
Imagine that in one generation, two brown beetles happened to have four offspring survive to reproduce. Several green beetles were killed when someone stepped on them and had no offspring. The next generation would have a few more brown beetles than the previous generation — but just by chance. These chance changes from generation to generation are known as genetic drift.

Natural selection
Imagine that green beetles are easier for birds to spot (and hence, eat). Brown beetles are a little more likely to survive to produce offspring. They pass their genes for brown coloration on to their offspring. So in the next generation, brown beetles are more common than in the previous generation.

All of these mechanisms can cause changes in the frequencies of genes in populations, and so all of them are mechanisms of evolutionary change. However, natural selection and genetic drift cannot operate unless there is genetic variation — that is, unless some individuals are genetically different from others. If the population of beetles were 100% green, selection and drift would not have any effect because their genetic make-up could not change.

So, what are the sources of genetic variation?

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Mechanisms of change Each of these four processes is a basic mechanism of evolutionary change. Mutation A mutation could cause parents with genes for bright green coloration to have offspring with a gene for brown coloration. That would make genes for brown coloration more frequent in the population than they were before the mutation.

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part 3

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Understanding Evolution - Your one-stop source for information on evolution

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Without genetic variation, some key mechanisms of evolutionary change like natural selection and genetic drift cannot operate.

There are three primary sources of new genetic variation:

1. Mutations are changes in the information contained in genetic material. (For most of life, this means a change in the sequence of DNA.) A single mutation can have a large effect, but in many cases, evolutionary change is based on the accumulation of many mutations with small effects.

2. Gene flow is any movement of genetic material from one population to another (e.g., through migration) and is an important source of genetic variation.

3. Sex can introduce new gene combinations into a population. This genetic shuffling is another important source of genetic variation.

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Genetic variation - Understanding Evolution

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Without genetic variation, some key mechanisms of evolutionary change like natural selection and genetic drift cannot operate. There are three primary sources of new genetic variation: Mutations are changes in the information contained in genetic material. (For most of life, this means a change in the sequence of DNA.)

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Mutations

Mutation is a change in DNA, the hereditary material of life. An organism's DNA affects how it looks, how it behaves, and its physiology — all aspects of its life. So a change in an organism's DNA can cause changes in all aspects of its life.

Mutations are random
Mutations can be beneficial, neutral, or harmful for the organism, but mutations do not "try" to supply what the organism "needs." In this respect, mutations are random — whether a particular mutation happens or not is unrelated to how useful that mutation would be.

Not all mutations matter to evolution
Since all cells in our body contain DNA, there are lots of places for mutations to occur; however, not all mutations matter for evolution. Somatic mutations occur in non-reproductive cells and won't be passed onto offspring.

For example, the golden color on half of this Red Delicious apple was caused by a somatic mutation. The seeds of this apple do not carry the mutation.

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Mutations Mutation is a change in DNA, the hereditary material of life. An organism's DNA affects how it looks, how it behaves, and its physiology - all aspects of its life. So a change in an organism's DNA can cause changes in all aspects of its life.

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The causes of mutations

Mutations happen for several reasons.

1. DNA fails to copy accurately
Most of the mutations that we think matter to evolution are "naturally-occurring." For example, when a cell divides, it makes a copy of its DNA — and sometimes the copy is not quite perfect. That small difference from the original DNA sequence is a mutation.

2. External influences can create mutations
Mutations can also be caused by exposure to specific chemicals or radiation. These agents cause the DNA to break down. This is not necessarily unnatural — even in the most isolated and pristine environments, DNA breaks down. Nevertheless, when the cell repairs the DNA, it might not do a perfect job of the repair. So the cell would end up with DNA slightly different than the original DNA and hence, a mutation.

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The causes of mutations Mutations happen for several reasons. DNA fails to copy accurately Most of the mutations that we think matter to evolution are "naturally-occurring." For example, when a cell divides, it makes a copy of its DNA - and sometimes the copy is not quite perfect.

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Gene flow

Gene flow — also called migration — is any movement of individuals, and/or the genetic material they carry, from one population to another. Gene flow includes lots of different kinds of events, such as pollen being blown to a new destination or people moving to new cities or countries. If gene versions are carried to a population where those gene versions previously did not exist, gene flow can be a very important source of genetic variation. In the graphic below, the gene version for brown coloration moves from one population to another.

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Gene flow Gene flow - also called migration - is any movement of individuals, and/or the genetic material they carry, from one population to another. Gene flow includes lots of different kinds of events, such as pollen being blown to a new destination or people moving to new cities or countries.

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Sex and genetic shuffling

Sex can introduce new gene combinations into a population and is an important source of genetic variation.
You probably know from experience that siblings are not genetically identical to their parents or to each other (except, of course, for identical twins). That's because when organisms reproduce sexually, some genetic "shuffling" occurs, bringing together new combinations of genes. For example, you might have bushy eyebrows and a big nose since your mom had genes associated with bushy eyebrows and your dad had genes associated with a big nose. These combinations can be good, bad, or neutral. If your spouse is wild about the bushy eyebrows/big nose combination, you were lucky and hit on a winning combination!

This shuffling is important for evolution because it can introduce new combinations of genes every generation. However, it can also break up "good" combinations of genes.

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Sex and genetic shuffling Sex can introduce new gene combinations into a population and is an important source of genetic variation. You probably know from experience that siblings are not genetically identical to their parents or to each other (except, of course, for identical twins).

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Development

Development is the process through which an embryo becomes an adult organism and eventually dies. Through development, an organism's genotype is expressed as a phenotype, exposing genes to the action of natural selection.

Studies of development are important to evolutionary biology for several reasons:

Explaining major evolutionary change
Changes in the genes controlling development can have major effects on the morphology of the adult organism. Because these effects are so significant, scientists suspect that changes in developmental genes have helped bring about large-scale evolutionary transformations. Developmental changes may help explain, for example, how some hoofed mammals evolved into ocean-dwellers, how water plants invaded the land, and how small, armored invertebrates evolved wings.

Learning about evolutionary history
An organism's development may contain clues about its history that biologists can use to build evolutionary trees.

Limiting evolutionary change
Developmental processes may constrain evolution, preventing certain characters from evolving in certain lineages. For example, development may help explain why there are no truly six-fingered tetrapods.

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Development Development is the process through which an embryo becomes an adult organism and eventually dies. Through development, an organism's genotype is expressed as a phenotype, exposing genes to the action of natural selection. Studies of development are important to evolutionary biology for several reasons: Explaining major evolutionary change Changes in the genes controlling development can have major effects on the morphology of the adult organism.

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Understanding Evolution - Your one-stop source for information on evolution

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Genetic drift is one of the basic mechanisms of evolution.

In each generation, some individuals may, just by chance, leave behind a few more descendants (and genes, of course!) than other individuals. The genes and other genetic elements of the next generation will be those of the "lucky" individuals, not necessarily the healthier or "better" individuals. That, in a nutshell, is genetic drift. It happens to ALL populations - there's no avoiding the vagaries of chance.

Earlier we used this hypothetical cartoon. Genetic drift affects the genetic makeup of the population, but unlike natural selection, through an entirely random process. So although genetic drift is a mechanism of evolution, it doesn't work to produce adaptations.

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Genetic drift is one of the basic mechanisms of evolution. In each generation, some individuals may, just by chance, leave behind a few more descendants (and genes, of course!) than other individuals.

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Understanding Evolution - Your one-stop source for information on evolution

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Evolutionary biologists use the word fitness to describe how good a particular genotype is at leaving offspring in the next generation relative to other genotypes. So if brown beetles consistently leave more offspring than green beetles because of their color, you'd say that the brown beetles had a higher fitness. In evolution, fitness is about success at surviving and reproducing, not about exercise and strength.

Of course, fitness is a relative thing. A genotype's fitness depends on the environment in which the organism lives. The fittest genotype during an ice age, for example, is probably not the fittest genotype once the ice age is over.

Fitness is a handy concept because it lumps everything that matters to natural selection (survival, mate-finding, reproduction) into one idea. The fittest individual is not necessarily the strongest, fastest, or biggest. A genotype's fitness includes its ability to survive, find a mate, produce offspring - and ultimately leave its genes in the next generation.

Caring for your offspring (above left), producing thousands of young - many of whom won't survive (above right) - and sporting fancy feathers that attract females (left) are a burden to the health and survival of the parent. These strategies do, however, increase fitness because they help the parents get more of their offspring into the next generation.

We tend to think of natural selection acting on survival ability - but, as the concept of fitness shows, that's only half the story. When natural selection acts on mate-finding and reproductive behavior, biologists call it sexual selection.

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Evolutionary fitness - Understanding Evolution

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Evolutionary biologists use the word fitness to describe how good a particular genotype is at leaving offspring in the next generation relative to other genotypes. So if brown beetles consistently leave more offspring than green beetles because of their color, you'd say that the brown beetles had a higher fitness.

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When an animal or plant arrives at an island for the first time, the new environment will usually be different from the one it's used to. As a result, a species will gradually adapt to survive or die out.
Over time, its appearance, behaviour and the way its body works might change - to become more successful at evading a predator, or more efficient at exploiting a new food source. For example, it might develop longer limbs, or lose those it no longer needs. Eventually, it may alter so much that it can no longer breed with its original species: it's evolved into an entirely new species.

An island, especially a remote one, may be colonised by relatively few species. This allows the members of one species to exploit numerous different lifestyles, or 'niches' - a phenomenon called adaptive radiation. As the individual groups adapt to their different niches, they may evolve into distinct species. This is how one ancestor can eventually lead to the evolution of many new species - often looking and behaving quite different from each other.

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Why do islands give rise to such unusual creatures?

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When an animal or plant arrives at an island for the first time, the new environment will usually be different from the one it's used to. As a result, a species will gradually adapt to survive or die out.