Scrooge
27-03-2008, 17:19
Exposing the flaws in the Theory of Evolution Monday, 24 March 2008 This article will describe and explore the Theory of Evolution. It will attempt to describe the theory, defining its main elements, and also take a brief look at the historical changes to the Theory – a kind of evolution of the Theory of Evolution! In addition, the article will seek to discuss the evidences used by the proponents of this theory and then provide a synopsis of the counter arguments.
Introduction
The Theory of Evolution has become the de facto standard used in the West, and indeed beyond, to explain the existence of creation and life. It is described as rational and scientific; many statements are made to demonstrate the strength of the Theory – such as the number of scientists who have given it their blessings and its widespread acceptance beyond the scientific community. Nonetheless, there is a strong perception existing in our day and age of the credibility of the Theory of Evolution. To some extent, it is discussed and taught in schools and educational establishments and promoted in the mainstream media. In stark contrast, other arguments that explain the existence of life are considered to be irrational, backward and steeped in ignorance borne out of belief in religion. In other words, there are essentially two clear camps: the ‘scientific’ and progressive camp which espouses the virtues of the Theory, and the apparently ‘unscientific’ contingent which clings to outmoded explanations such as the existence of a Creator. In recent times, thanks in no small part to various Christian elements in the U.S., the clashes between these two sides have become more visible and the tempo seems to have been raised. There have been calls for a restructuring to the way in which the Theory is taught to children, or at the very least provision for a balanced approach, so that the young are taught about other explanations as well. Many establishments have insisted on giving religious teaching the priority, leading to conflict with those who believe religion should have no such role in schools.
The Theory of Evolution
The theory of evolution is sometimes described using complex and convoluted language, which can be a significant source of confusion. What adds to the confusion is the fact that aspects of the theory do undergo change and revision. In this article I will try to explain the main points that constitute the theory, on which those who propose this theory are agreed, without getting bogged down in the finer details or indeed the many arguments and assumptions in relation to areas where there may be some difference of opinion and divergence of views. I have also tried to simplify the description so it can be understood without recourse to a dictionary and constant definition of scientific terminology.
To understand the thrust of the theory, it is useful to have an idea of some of the concepts that are used and an appreciation of the context.
Firstly, the definition: biological evolution is defined as descent with modification from a common ancestor. In this context, descent means going down from one generation through to the following generations. Modification alludes to alterations in genetic make-up and changes in gene frequencies. This definition encompasses what is known as small-scale evolution (changes in gene frequency in a population from one generation to the next) and large-scale evolution (the descent of different species from a common ancestor over many generations).
Of course biological evolution is not simply a matter of change over time. Lots of things change over time: trees lose their leaves, mountain ranges rise and erode, but they aren't examples of biological evolution because they don't involve descent through genetic inheritance.
Secondly, a key central idea of biological evolution is that all life on Earth shares a common ancestor, just as our cousins and we share a common grandmother. It is argued that through the process of descent with modification, the common ancestor of life on Earth gave rise to the diversity that we see documented in the fossil record and around us today. Evolution means that we are all distant cousins: humans and oak trees, hummingbirds and whales.
The process of evolution produces a pattern of relationships between species. As lineages evolve and split and modifications are inherited, their evolutionary paths diverge. This produces a branching pattern of evolutionary relationships. These relationships can be reconstructed and represented on a "family tree," called a phylogeny.
As a consequence of this ‘family tree’ understanding, it is important to remember that:
1. Humans did not evolve from chimpanzees. Humans and chimpanzees are evolutionary cousins and share a recent common ancestor that was neither chimpanzee nor human.
2. Humans are not "higher" or "more evolved" than other living lineages. Since these lineages split, humans and chimpanzees have each evolved traits unique to their own lineages.
Thirdly, another important aspect of evolution is the linking of speciation events to time i.e. trying to understand when different species evolved. Using various methods, such as radiometric dating, scientists are able to conclude that life began 3.8 billion years ago, and insects diversified 290 million years ago, but the human and chimpanzee lineages diverged only five million years ago.
To give an analogy for this, imagine squeezing the billions of years of the history of life on Earth into a single minute. Then it would take about 50 seconds for multi-cellular life to evolve, another four seconds for vertebrates to invade the land, and another four seconds for flowers to evolve — and only in the last 0.002 seconds would "modern" humans arise.
So, the claim is made that evolution is the process by which modern organisms have descended from ancient ancestors. Evolution is apparently responsible for both the remarkable similarities we see across all life and the amazing diversity of that life — but exactly how does it work?
Fundamental to the process is genetic variation upon which selective forces can act in order for evolution to occur. 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. Therefore, we need to examine the actual mechanisms of evolution.
In essence there are four basic processes, which constitute the mechanisms of evolution. These are mutation, migration, genetic drift and natural selection.
Mutation refers to the actual changes in the DNA within cells. The DNA affects how an organism looks, behaves and so on. Thus a change in the DNA can alter all aspects of its life.
When cells divide the DNA is copied exactly as it is. However, on occasion, it is possible for they’re to be a discrepancy in the copying of the DNA. This difference is considered a mutation. It must be kept in mind that mutations are random – and so do not normally depend on external factors. That said, it is possible for there to be mutation as a result of exposure to radiation or chemicals, causing the DNA to break down. In this case, when the cells repair the DNA, the result is not a perfect repair – and so the resultant DNA is a mutation.
Whether a particular mutation occurs is not related to how useful that mutation would be. The mutation in the genes can yield a beneficial, neutral or harmful change for the organism.
Although mutation can occur with any gene, it is the mutation that affects genes, which can be transmitted from one generation to the next that is of interest, since this is a form of evolution. If genes mutate and cannot be passed to future generations, then these mutations cannot be considered as having any relation to evolution. These are called Somatic Mutations and occur in non-reproductive cells. Hence the genes that are affected by mutation related to biological evolution are the reproductive cells, like eggs and sperm. Any mutations in the sex cells mean that potentially the change (the mutation) can be passed onto following generations. These mutations are labelled Germ Line Mutations.
Migration is the flow of genes from one population to another. This Gene Flow can include various different events, such as pollen being blown to a new destination or people moving to new cities or countries. In a situation where genes are carried to a population where those genes previously did not exist, gene flow becomes a very important source of genetic variation.
Thus, as well as being mechanisms of evolution, Mutation and Migration also constitute sources of genetic variation. Another source of genetic variation is sex, which can introduce new gene combinations into a population.
Genetic drift refers to the situation where, just ‘by chance’, some individuals leave behind a few more descendents and thus genes than other individuals. This happens to all populations since there can be no avoidance of chance. So for example, every time somebody steps on an insect with a certain characteristic, this reduces the number within that particular population and hence means there is one less insect remaining to pass on its genes to a new generation. Conversely, this also means that there are now more insects with different characteristics within the same population, who are able to pass on their genes. Clearly, this shows that genetic drift affects the genetic makeup of a population through entirely random means.
Natural Selection is the fourth cog in the wheel of evolution. This in itself requires three components: variation in traits, differential reproduction and heredity. To understand this, consider a population of beetles. Some beetles are brown and others are green – this is a variation in a trait or a characteristic.
The environment is not able to support unlimited growth of the population and so not all individuals are able to reproduce to their full potential. For example, we could say that green beetles are easily visible on the ground and so tend to get eaten more by birds – so less survive to reproduce compared to brown beetles. In other words, we have differential reproduction.
Finally, the brown beetles have brown baby beetles since this trait has a genetic basis i.e. they pass on a gene that determines the colour to be brown. This is what is meant by heredity. Putting these components together, evolution by natural selection is seen at work. The more advantageous trait of brown colour becomes more common in the population with time and if this process continues, then eventually all the beetles will be brown.
It is claimed that natural selection is also able to shape behaviour. The mating rituals that many birds have, the wiggle dance that bee’s do or the human capacity to learn language, have genetic components.
In some cases, natural selection can be observed directly. Data shows that the shape of finches' beaks on the Galapagos Islands is related to weather patterns: after droughts, the finch population has deeper, stronger beaks that let them eat tougher seeds.
In other cases, human activity has led to environmental changes that have caused populations to evolve through natural selection. A striking example is that of the population of dark moths in the 19th century in England, which rose and fell in parallel to industrial pollution. These changes can often be observed and documented.
‘Fitness’ is a concept used to describe how good a particular organism is at leaving its set of genes in the next generation compared with others with a different set of genes. Going back to the example of beetles, if brown beetles were to consistently leave more off spring than green beetles, then they would be considered to have a higher fitness. Fitness however does depend on the environment in which an organism lives. Also, from this perspective, the fittest individual is not necessarily the strongest, fastest or biggest. What matters is leaving it’s genes in the next generation and so survival ability, finding a mate and producing off spring is more important. This sub-category of natural selection in relation to finding a mate and reproductive behaviour is labelled sexual selection.
Another category of natural selection is artificial selection. This is where, instead of nature, humans consciously select for or against particular features in organisms. For example, the human may allow only organisms with the desired feature to reproduce or may provide more resources to the organisms with the desired feature. Historically, farmers and breeders have used this idea of selection to cause major changes in the features of their plants and animals.
One key aspect of natural selection is known as adaptation. An adaptation is a feature that is common in a population because it seems to provide an improved function. Adaptations can take many forms: a behaviour that allows better evasion of predators, a protein that functions better at body temperature, or an anatomical feature that allows the organism to access a valuable new resource — all of these might be adaptations. For example, mimicry of leaves by insects is an adaptation for evading predators or the use of echolocation by bats to help them catch insects. Similarly, the creosote bush is a desert-dwelling plant that produces toxins that prevent other plants from growing nearby, thus reducing competition for nutrients and water.
To summarise, all of the mechanisms discussed above (mutation, migration, genetic drift and natural selection) can cause changes in the frequencies of genes in populations, and so all of them are mechanisms of evolutionary change. However, it is worth keeping in mind that natural selection and genetic drift cannot operate unless there is genetic variation — that is, unless some individuals are genetically different from others.
A historical perspective
Although Charles Darwin is synonymous with the Theory of Evolution, he was not the first naturalist to propose that species changed over time into new species i.e. that life evolves. In the eighteenth century, a naturalist called Buffon along with others began to introduce the idea that life might not have been fixed since creation. By the end of the 1700s, palaeontologists had swelled the fossil collections of Europe, offering a picture of the past at odds with an unchanging natural world. And in 1801, a French naturalist named Jean Baptiste Pierre Antoine de Monet; Chevalier de Lamarck took a great conceptual step and proposed a full-blown theory of evolution.
Lamarck was struck by the similarities of many of the animals he studied, and was impressed too by the burgeoning fossil record. It led him to argue that life was not fixed. When environments changed, organisms had to change their behaviour to survive. If they began to use an organ more than they had in the past, it would increase in its lifetime. If a giraffe stretched its neck for leaves, for example, a "nervous fluid" would flow into its neck and make it longer. Its offspring would inherit the longer neck, and continued stretching would make it longer still over several generations. Meanwhile organs that organisms stopped using would shrink (called vestigial structures).
Lamarck was mocked and attacked by many of his contemporary naturalists such as Cuvier. While they questioned him on scientific grounds, many of them were also disturbed by the theological implications of his work. Lamarck was proposing that life took on its current form through natural processes, not through miraculous interventions. For British naturalists in particular, steeped as they were in natural theology, this was appalling. They believed that nature was a reflection of God's benevolent design. To them, it seemed Lamarck was claiming that it was the result of blind primal forces. Shunned by the scientific community, Lamarck died in 1829 in poverty and obscurity.
In many ways, Darwin's central argument was very different from Lamarck's. He argued that complexity evolved simply as a result of life adapting to its local conditions from one generation to the next. He also argued that species could go extinct rather than change into new forms. But Darwin relied on much the same evidence for evolution that Lamarck did and Darwin wrongly accepted that changes acquired during an organism's lifetime could be passed on to its offspring.
Lamarckian inheritance remained popular throughout the 1800s, in large part because scientists did not yet understand how heredity works. With the discovery of genes, it was finally abandoned for the most part. But Lamarck, whom Darwin described as "this justly celebrated naturalist," remains a major figure in the history of biology for envisioning evolutionary change for the first time.
Throughout the nineteenth century, heredity remained a puzzle to scientists. How was it that children ended up looking similar to, but not exactly like, their parents? These questions fascinated and frustrated Charles Darwin deeply. After all, heredity lies at the heart of evolution.
Ironically, it was just as Darwin was publishing the Origin of Species in 1859 that someone got the first real glimpse of the biological machinery behind heredity. In a secluded monastery in what is now the Czech Republic, a monk named Gregor Mendel was studying heredity in a garden of peas. Through his experiments, Mendel discovered what later scientists called "dominant" and "recessive" alleles i.e. part of genetics.
Darwin and a British biologist called Alfred Russel Wallace had independently conceived of a natural, even observable, way for life to change: a process Darwin called natural selection. Within a few decades, most scientists accepted that evolution and the descent of species from common ancestors were real. But natural selection had a harder time finding acceptance.
Even in 1900, whilst many scientists were rediscovering Mendel's insights, they continued to remain opposed to natural selection. After all, Darwin had talked of natural selection gradually altering a species by working on tiny variations. But the Mendelist’s found major differences between traits encoded by alleles. In order to jump from one allele to another, evolution must make giant jumps—an idea that seemed to clash with Darwin.
But in the 1920s geneticists began to recognize that natural selection could indeed act on genes. For one thing, it became clear that any given trait was usually the product of many genes rather than a single one. A mutation to any one of the genes involved could create small changes to the trait rather than some drastic transformation. Just as importantly, several scientists — foremost among them Ronald Fisher, JBS Haldane and Sewall Wright — showed how natural selection could operate in a Mendelian world. They carried out breeding experiments like previous geneticists, but they also did something new: they built sophisticated mathematical models of evolution.
Known as "population genetics," their approach revealed how mutations arise and, if they are favoured by natural selection, can spread through a population. Even a slight advantage can let genes spread rapidly through a group of animals or plants and drive other forms extinct. Evolution, these population geneticists argued, is carried out mainly by small mutations, since drastic mutations would almost always be harmful rather than helpful.
Thus, population genetics became one of the key elements of what would be called the Modern Synthesis.
In 1937, a Soviet-born geneticist named Theodosius Dobzhansky wrote a landmark book called Genetics and the Origin of Species. Dobzhansky's ability to combine genetics and natural history attracted many other biologists to join him in the effort to find a unified explanation of how evolution happens. Their combined work known as "The Modern Synthesis" brought together genetics, palaeontology and many other sciences into one powerful explanation of evolution, showing how mutations and natural selection could produce large-scale evolutionary change.
While evolutionary biologists were fashioning the Modern Synthesis, geneticists around the world searched furiously for the molecules that carried genetic information. They knew that cells contained several different types of molecules, such as proteins and nucleic acids. But which had the capacity to bear information and be copied into new cells?
The answer came through the discovery of DNA by Francis Crick and James Watson, which revolutionized evolutionary biology. Mutations, researchers realized, change the structure of the DNA. A single base pair may change, or a set of genes may be duplicated. Hence, those mutations that confer a selective advantage to an individual become more common over time, and ultimately these mutant genes could drive the older versions out of existence.
Introduction
The Theory of Evolution has become the de facto standard used in the West, and indeed beyond, to explain the existence of creation and life. It is described as rational and scientific; many statements are made to demonstrate the strength of the Theory – such as the number of scientists who have given it their blessings and its widespread acceptance beyond the scientific community. Nonetheless, there is a strong perception existing in our day and age of the credibility of the Theory of Evolution. To some extent, it is discussed and taught in schools and educational establishments and promoted in the mainstream media. In stark contrast, other arguments that explain the existence of life are considered to be irrational, backward and steeped in ignorance borne out of belief in religion. In other words, there are essentially two clear camps: the ‘scientific’ and progressive camp which espouses the virtues of the Theory, and the apparently ‘unscientific’ contingent which clings to outmoded explanations such as the existence of a Creator. In recent times, thanks in no small part to various Christian elements in the U.S., the clashes between these two sides have become more visible and the tempo seems to have been raised. There have been calls for a restructuring to the way in which the Theory is taught to children, or at the very least provision for a balanced approach, so that the young are taught about other explanations as well. Many establishments have insisted on giving religious teaching the priority, leading to conflict with those who believe religion should have no such role in schools.
The Theory of Evolution
The theory of evolution is sometimes described using complex and convoluted language, which can be a significant source of confusion. What adds to the confusion is the fact that aspects of the theory do undergo change and revision. In this article I will try to explain the main points that constitute the theory, on which those who propose this theory are agreed, without getting bogged down in the finer details or indeed the many arguments and assumptions in relation to areas where there may be some difference of opinion and divergence of views. I have also tried to simplify the description so it can be understood without recourse to a dictionary and constant definition of scientific terminology.
To understand the thrust of the theory, it is useful to have an idea of some of the concepts that are used and an appreciation of the context.
Firstly, the definition: biological evolution is defined as descent with modification from a common ancestor. In this context, descent means going down from one generation through to the following generations. Modification alludes to alterations in genetic make-up and changes in gene frequencies. This definition encompasses what is known as small-scale evolution (changes in gene frequency in a population from one generation to the next) and large-scale evolution (the descent of different species from a common ancestor over many generations).
Of course biological evolution is not simply a matter of change over time. Lots of things change over time: trees lose their leaves, mountain ranges rise and erode, but they aren't examples of biological evolution because they don't involve descent through genetic inheritance.
Secondly, a key central idea of biological evolution is that all life on Earth shares a common ancestor, just as our cousins and we share a common grandmother. It is argued that through the process of descent with modification, the common ancestor of life on Earth gave rise to the diversity that we see documented in the fossil record and around us today. Evolution means that we are all distant cousins: humans and oak trees, hummingbirds and whales.
The process of evolution produces a pattern of relationships between species. As lineages evolve and split and modifications are inherited, their evolutionary paths diverge. This produces a branching pattern of evolutionary relationships. These relationships can be reconstructed and represented on a "family tree," called a phylogeny.
As a consequence of this ‘family tree’ understanding, it is important to remember that:
1. Humans did not evolve from chimpanzees. Humans and chimpanzees are evolutionary cousins and share a recent common ancestor that was neither chimpanzee nor human.
2. Humans are not "higher" or "more evolved" than other living lineages. Since these lineages split, humans and chimpanzees have each evolved traits unique to their own lineages.
Thirdly, another important aspect of evolution is the linking of speciation events to time i.e. trying to understand when different species evolved. Using various methods, such as radiometric dating, scientists are able to conclude that life began 3.8 billion years ago, and insects diversified 290 million years ago, but the human and chimpanzee lineages diverged only five million years ago.
To give an analogy for this, imagine squeezing the billions of years of the history of life on Earth into a single minute. Then it would take about 50 seconds for multi-cellular life to evolve, another four seconds for vertebrates to invade the land, and another four seconds for flowers to evolve — and only in the last 0.002 seconds would "modern" humans arise.
So, the claim is made that evolution is the process by which modern organisms have descended from ancient ancestors. Evolution is apparently responsible for both the remarkable similarities we see across all life and the amazing diversity of that life — but exactly how does it work?
Fundamental to the process is genetic variation upon which selective forces can act in order for evolution to occur. 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. Therefore, we need to examine the actual mechanisms of evolution.
In essence there are four basic processes, which constitute the mechanisms of evolution. These are mutation, migration, genetic drift and natural selection.
Mutation refers to the actual changes in the DNA within cells. The DNA affects how an organism looks, behaves and so on. Thus a change in the DNA can alter all aspects of its life.
When cells divide the DNA is copied exactly as it is. However, on occasion, it is possible for they’re to be a discrepancy in the copying of the DNA. This difference is considered a mutation. It must be kept in mind that mutations are random – and so do not normally depend on external factors. That said, it is possible for there to be mutation as a result of exposure to radiation or chemicals, causing the DNA to break down. In this case, when the cells repair the DNA, the result is not a perfect repair – and so the resultant DNA is a mutation.
Whether a particular mutation occurs is not related to how useful that mutation would be. The mutation in the genes can yield a beneficial, neutral or harmful change for the organism.
Although mutation can occur with any gene, it is the mutation that affects genes, which can be transmitted from one generation to the next that is of interest, since this is a form of evolution. If genes mutate and cannot be passed to future generations, then these mutations cannot be considered as having any relation to evolution. These are called Somatic Mutations and occur in non-reproductive cells. Hence the genes that are affected by mutation related to biological evolution are the reproductive cells, like eggs and sperm. Any mutations in the sex cells mean that potentially the change (the mutation) can be passed onto following generations. These mutations are labelled Germ Line Mutations.
Migration is the flow of genes from one population to another. This Gene Flow can include various different events, such as pollen being blown to a new destination or people moving to new cities or countries. In a situation where genes are carried to a population where those genes previously did not exist, gene flow becomes a very important source of genetic variation.
Thus, as well as being mechanisms of evolution, Mutation and Migration also constitute sources of genetic variation. Another source of genetic variation is sex, which can introduce new gene combinations into a population.
Genetic drift refers to the situation where, just ‘by chance’, some individuals leave behind a few more descendents and thus genes than other individuals. This happens to all populations since there can be no avoidance of chance. So for example, every time somebody steps on an insect with a certain characteristic, this reduces the number within that particular population and hence means there is one less insect remaining to pass on its genes to a new generation. Conversely, this also means that there are now more insects with different characteristics within the same population, who are able to pass on their genes. Clearly, this shows that genetic drift affects the genetic makeup of a population through entirely random means.
Natural Selection is the fourth cog in the wheel of evolution. This in itself requires three components: variation in traits, differential reproduction and heredity. To understand this, consider a population of beetles. Some beetles are brown and others are green – this is a variation in a trait or a characteristic.
The environment is not able to support unlimited growth of the population and so not all individuals are able to reproduce to their full potential. For example, we could say that green beetles are easily visible on the ground and so tend to get eaten more by birds – so less survive to reproduce compared to brown beetles. In other words, we have differential reproduction.
Finally, the brown beetles have brown baby beetles since this trait has a genetic basis i.e. they pass on a gene that determines the colour to be brown. This is what is meant by heredity. Putting these components together, evolution by natural selection is seen at work. The more advantageous trait of brown colour becomes more common in the population with time and if this process continues, then eventually all the beetles will be brown.
It is claimed that natural selection is also able to shape behaviour. The mating rituals that many birds have, the wiggle dance that bee’s do or the human capacity to learn language, have genetic components.
In some cases, natural selection can be observed directly. Data shows that the shape of finches' beaks on the Galapagos Islands is related to weather patterns: after droughts, the finch population has deeper, stronger beaks that let them eat tougher seeds.
In other cases, human activity has led to environmental changes that have caused populations to evolve through natural selection. A striking example is that of the population of dark moths in the 19th century in England, which rose and fell in parallel to industrial pollution. These changes can often be observed and documented.
‘Fitness’ is a concept used to describe how good a particular organism is at leaving its set of genes in the next generation compared with others with a different set of genes. Going back to the example of beetles, if brown beetles were to consistently leave more off spring than green beetles, then they would be considered to have a higher fitness. Fitness however does depend on the environment in which an organism lives. Also, from this perspective, the fittest individual is not necessarily the strongest, fastest or biggest. What matters is leaving it’s genes in the next generation and so survival ability, finding a mate and producing off spring is more important. This sub-category of natural selection in relation to finding a mate and reproductive behaviour is labelled sexual selection.
Another category of natural selection is artificial selection. This is where, instead of nature, humans consciously select for or against particular features in organisms. For example, the human may allow only organisms with the desired feature to reproduce or may provide more resources to the organisms with the desired feature. Historically, farmers and breeders have used this idea of selection to cause major changes in the features of their plants and animals.
One key aspect of natural selection is known as adaptation. An adaptation is a feature that is common in a population because it seems to provide an improved function. Adaptations can take many forms: a behaviour that allows better evasion of predators, a protein that functions better at body temperature, or an anatomical feature that allows the organism to access a valuable new resource — all of these might be adaptations. For example, mimicry of leaves by insects is an adaptation for evading predators or the use of echolocation by bats to help them catch insects. Similarly, the creosote bush is a desert-dwelling plant that produces toxins that prevent other plants from growing nearby, thus reducing competition for nutrients and water.
To summarise, all of the mechanisms discussed above (mutation, migration, genetic drift and natural selection) can cause changes in the frequencies of genes in populations, and so all of them are mechanisms of evolutionary change. However, it is worth keeping in mind that natural selection and genetic drift cannot operate unless there is genetic variation — that is, unless some individuals are genetically different from others.
A historical perspective
Although Charles Darwin is synonymous with the Theory of Evolution, he was not the first naturalist to propose that species changed over time into new species i.e. that life evolves. In the eighteenth century, a naturalist called Buffon along with others began to introduce the idea that life might not have been fixed since creation. By the end of the 1700s, palaeontologists had swelled the fossil collections of Europe, offering a picture of the past at odds with an unchanging natural world. And in 1801, a French naturalist named Jean Baptiste Pierre Antoine de Monet; Chevalier de Lamarck took a great conceptual step and proposed a full-blown theory of evolution.
Lamarck was struck by the similarities of many of the animals he studied, and was impressed too by the burgeoning fossil record. It led him to argue that life was not fixed. When environments changed, organisms had to change their behaviour to survive. If they began to use an organ more than they had in the past, it would increase in its lifetime. If a giraffe stretched its neck for leaves, for example, a "nervous fluid" would flow into its neck and make it longer. Its offspring would inherit the longer neck, and continued stretching would make it longer still over several generations. Meanwhile organs that organisms stopped using would shrink (called vestigial structures).
Lamarck was mocked and attacked by many of his contemporary naturalists such as Cuvier. While they questioned him on scientific grounds, many of them were also disturbed by the theological implications of his work. Lamarck was proposing that life took on its current form through natural processes, not through miraculous interventions. For British naturalists in particular, steeped as they were in natural theology, this was appalling. They believed that nature was a reflection of God's benevolent design. To them, it seemed Lamarck was claiming that it was the result of blind primal forces. Shunned by the scientific community, Lamarck died in 1829 in poverty and obscurity.
In many ways, Darwin's central argument was very different from Lamarck's. He argued that complexity evolved simply as a result of life adapting to its local conditions from one generation to the next. He also argued that species could go extinct rather than change into new forms. But Darwin relied on much the same evidence for evolution that Lamarck did and Darwin wrongly accepted that changes acquired during an organism's lifetime could be passed on to its offspring.
Lamarckian inheritance remained popular throughout the 1800s, in large part because scientists did not yet understand how heredity works. With the discovery of genes, it was finally abandoned for the most part. But Lamarck, whom Darwin described as "this justly celebrated naturalist," remains a major figure in the history of biology for envisioning evolutionary change for the first time.
Throughout the nineteenth century, heredity remained a puzzle to scientists. How was it that children ended up looking similar to, but not exactly like, their parents? These questions fascinated and frustrated Charles Darwin deeply. After all, heredity lies at the heart of evolution.
Ironically, it was just as Darwin was publishing the Origin of Species in 1859 that someone got the first real glimpse of the biological machinery behind heredity. In a secluded monastery in what is now the Czech Republic, a monk named Gregor Mendel was studying heredity in a garden of peas. Through his experiments, Mendel discovered what later scientists called "dominant" and "recessive" alleles i.e. part of genetics.
Darwin and a British biologist called Alfred Russel Wallace had independently conceived of a natural, even observable, way for life to change: a process Darwin called natural selection. Within a few decades, most scientists accepted that evolution and the descent of species from common ancestors were real. But natural selection had a harder time finding acceptance.
Even in 1900, whilst many scientists were rediscovering Mendel's insights, they continued to remain opposed to natural selection. After all, Darwin had talked of natural selection gradually altering a species by working on tiny variations. But the Mendelist’s found major differences between traits encoded by alleles. In order to jump from one allele to another, evolution must make giant jumps—an idea that seemed to clash with Darwin.
But in the 1920s geneticists began to recognize that natural selection could indeed act on genes. For one thing, it became clear that any given trait was usually the product of many genes rather than a single one. A mutation to any one of the genes involved could create small changes to the trait rather than some drastic transformation. Just as importantly, several scientists — foremost among them Ronald Fisher, JBS Haldane and Sewall Wright — showed how natural selection could operate in a Mendelian world. They carried out breeding experiments like previous geneticists, but they also did something new: they built sophisticated mathematical models of evolution.
Known as "population genetics," their approach revealed how mutations arise and, if they are favoured by natural selection, can spread through a population. Even a slight advantage can let genes spread rapidly through a group of animals or plants and drive other forms extinct. Evolution, these population geneticists argued, is carried out mainly by small mutations, since drastic mutations would almost always be harmful rather than helpful.
Thus, population genetics became one of the key elements of what would be called the Modern Synthesis.
In 1937, a Soviet-born geneticist named Theodosius Dobzhansky wrote a landmark book called Genetics and the Origin of Species. Dobzhansky's ability to combine genetics and natural history attracted many other biologists to join him in the effort to find a unified explanation of how evolution happens. Their combined work known as "The Modern Synthesis" brought together genetics, palaeontology and many other sciences into one powerful explanation of evolution, showing how mutations and natural selection could produce large-scale evolutionary change.
While evolutionary biologists were fashioning the Modern Synthesis, geneticists around the world searched furiously for the molecules that carried genetic information. They knew that cells contained several different types of molecules, such as proteins and nucleic acids. But which had the capacity to bear information and be copied into new cells?
The answer came through the discovery of DNA by Francis Crick and James Watson, which revolutionized evolutionary biology. Mutations, researchers realized, change the structure of the DNA. A single base pair may change, or a set of genes may be duplicated. Hence, those mutations that confer a selective advantage to an individual become more common over time, and ultimately these mutant genes could drive the older versions out of existence.