Evolutionary concepts first appeared in early Greek writings, for example, in the work of Anaximander and Empedocles. Anaximander proposed that animals could be transformed from one kind to another, and Empedocles speculated that they could be made up of various combinations of pre-existing parts.
However, evolutionary theories were subsequently prevented from developing and challenging the belief of special creation for some fifteen centuries, due to the restraining influence of the Church.
The growth of scientific observation and experimentation led to some theories of evolution beginning to emerge from the mid 16th Century. Despite the idea of human progress being central to the Enlightenment of the 18th Century, this did not lead to the theory of evolution. Pierre-Louis Moreau de Maupertuis proposed the spontaneous generation and extinction of organisms as part of his theory of origins. However, he advanced no theory of evolution.
Georges-Louis Leclerc, a prominent naturalist of the time, explicitly considered, and rejected, the possible descent of several species from a common ancestor.
The physician Erasmus Darwin, grandfather of Charles Darwin, offered some evolutionary speculations in his book Zoonomia, but they had no real influence on subsequent theories.
The Swedish Botanist, Carolus Linnaeus, who devised the hierarchical system of plant and animal classification that is still in use today in a modernised form, showed an inclination towards the ability of species to mutate, as a result of his observations of variations among species.
In the early 19th Century, the French naturalist Jean-Baptiste Lamarck presented a clearly stated evolutionary theory. This theory, later known as 'The Inheritance of Acquired Characteristics' was ridiculed at the time and thoroughly disproved in the 20th Century, although it did contribute to the gradual acceptance of biological evolution as well as stimulating later studies.
The founder of the modern theory of evolution was Charles Darwin. In 1859 the first edition of his On The Origin of The Species was published and it sold out in one day. The naturalist Alfred Wallace had also hit upon the idea of natural selection independently, however, his view differed from Darwin’s, most notably in that he did not think that natural selection was sufficient to account for the origin of man, but divine intervention had been required.
Herbert Spencer, a philosopher, was also an influence in evolutionary theory during the latter part of the 19th and early 20th Centuries. He popularised a number of slogans, including "survival of the fittest" which was taken up by Darwin in later editions of Origin of Species. Spencer’s ideas damaged proper understandings of natural selection and Darwin often attacked him for his "fundamental generalisations".
The main weakness of Darwin’s evolutionary theory lay in gaps in the explanations of the mechanism of evolution and the origin of species. The concept of natural selection is that inheritable variations among the individuals arise in nature and that some variations prove advantageous under prevailing conditions, in that they enable the organism to leave more surviving offspring. Darwin did not understand how these variations initially arise or are transmitted to offspring and subsequent generations.
The missing link in Darwin’s argument was provided by Mendelian genetics. Gregor Mendel was an Augustinian monk who carried out a long series of experiments with peas in the garden of his monastery. His paper, published in 1866, formulated the fundamental principles of the theory of heredity, and it is still current today.
Darwin did not know about these discoveries and they did not become generally known until 1900 when natural selection and Mendelian genetics were simultaneously rediscovered by scientists.
In the 1880s, German biologist August Weismann published his germ-plasm theory defending natural selection. His ideas became known as neo-Darwinism. The rediscovery of Mendel’s theory of heredity in 1900 led to an emphasis on the role of heredity on evolution. Hugo de Vries proposed a new theory of evolution known as mutationism, which discounted natural selection, and was heavily opposed by naturalists, especially biometricians. Biometricians, led by Karl Pearson, defended natural selection.
In the 1920s and 30s, theoretical geneticists including R.A. Fisher and J.B.S. Haldane in Britain and Sewall Wright in the United States, used mathematical arguments to support natural selection and contributed to the downfall of mutationism. They also provided a theoretical framework for the integration of genetics into Darwin's theory of natural selection.
In 1937 Theodosius Dobzhansky published Genetics and the Origin of Species, which combined Darwinian natural selection and Mendelian genetics. This led naturalists and experimental biologists to understand the process as one of genetic change in populations. This stimulated interest in evolutionary studies and scientists from a variety of biological fields contributed to the theories, most notably the zoologists Ernst Mayr and Sir Julian Huxley, the palaeontologist George G. Simpson and the botanist George Ledyard Stebbins.
By 1950 acceptance of Darwin's theory of evolution by natural selection was universal among biologists and it is now widely accepted in society and taught within schools. Some creationists still oppose it.
What is evolution?
Biological evolution is the theory that groups of organisms change with the passage of time, causing their descendants to differ morphologically and physiologically from their ancestors. This process is dependent on the need of organisms to compete for the things which are essential to them individually to survive and reproduce. It is a continuing process that has been going on for millions of years, rather than a finished event, although there is some debate over the degree to which human beings are evolving now.
What is natural selection?
Natural selection is the mechanism that drives evolutionary change. Put simply, it is a process whereby organisms best suited to their environment become the ones most likely to survive and leave descendants. It is also often referred to as "survival of the fittest", which conjures up images of the biggest, strongest individuals being the most successful, but in a biological sense, evolutionary fitness refers to the ability to reproduce in a particular environment as well as survive. Therefore organisms may be the "fittest" because they co-operate with other organisms, rather than competing with them. Charles Darwin, often known as the father of evolution, was the first person to document the operation of natural selection.
Darwin formulated the central argument of this theory from his observations, the existence of variations among animals. He reasoned that variations must occur in nature that are favourable or useful in some way to the organism in its struggle for existence. Favourable variations are ones that increase chances for survival and procreation. Those advantageous variations are preserved and multiplied from generation to generation at the expense of less advantageous ones. The outcome of the process is an organism that is well adapted to its environment.
How does natural selection occur?
The variations that occur are as a result of changes that are produced at the genetic level. They occur as an organism's genes mutate and/or recombine in different ways during reproduction and are passed on to future generations. Genes are the portions of an organism's DNA that carry the code responsible for building that organism in a very specific way. From generation to generation, molecular mechanisms reshuffle, duplicate, and alter genes in a way that produces genetic variation. This variation is the raw material for evolution. Mutations are 'mistakes' introduced into the genetic material used for reproduction, which can occur naturally, or as a result of something like exposure to radiation.
Positive mutations that give some benefit to the organism provide the new material for natural selection to operate on. This could lead to individuals inheriting new characteristics that give them a survival and reproductive advantage in their local environments; these characteristics tend to increase in frequency in the population, while those that are disadvantageous decrease in frequency. Any non-genetic changes that occur during an organism's life span, for example an increase in muscle mass, cannot be passed on to the next generation and are not examples of evolution.
Role of sexual reproduction in natural selection
Sexual reproduction allows an organism to combine half of its genes with half of another individual's genes, which means new combinations of genes are produced every generation. When eggs and sperm are produced, genetic material is shuffled and recombined in ways that produce new combinations of genes. Sexual reproduction therefore increases genetic variation, which increases the raw material on which natural selection operates. Genetic variation within a species, also known as genetic diversity, increases a species' opportunity for change over successive generations.
Evolution and religion
Like in the early days when evolutionary concepts were first developed, some creationists still strongly disagree with evolutionary theory, believing that it denies the presence of God. However, these days many people from evolutionary biologists to religious leaders, including Pope John Paul II, believe that evolutionary theory does not refute the presence of God.
They argue that evolution is the description of a process that governs the development of life on Earth, dealing only with objects, events and processes in the material world. Therefore, it does not say anything one way or another about the creation of the world.
The Arguments: Dr Anne Campbell
Dr Anne Campbell is a Reader in the Psychology Department, University of Durham. Dr Campbell is an evolutionary psychologist who thinks that you can't have a full understanding of the human mind without looking at how the process of evolution has shaped it.
On her area of interest:
The brain is as much an organ of the human body as any other, and I think it's important that we should look at the kind of natural and sexual pressures that lead to the kind of brains we have now. On the other hand, if it's the case that perhaps evolution is reaching its end, this may turn out to be a largely historical enterprise but may not guide us very far in making predictions about the future.
On giving entirely Darwinian explanations of the human mind:
I was just reminded that of course evolution is a process, a process of change over time, and it doesn't have to apply only to genes, there's no reason why it couldn't apply to a large number of other things. And of course, one thing could be human ideas. In fact, culture itself is usually defined as the social transmission of ideas from one generation to the next. We can see those ideas to some extent, as kind of particular forms that are subject to variation and to subject to selective retention and transmission. So in that sense you can apply the idea of evolution beyond merely genetics and into the kind of ideas that we take around with us all the time. The kind of inventions that we have are all subject to evolution.
On the idea that human evolution has stopped:
I think, in terms of genetic evolution, you can make a very strong case for that in the West. The major differences in fecundity and mortality between individuals have been minimised a very great deal. But that doesn't mean that evolution in terms of ideas has not accelerated, and, in fact, it accelerated massively, even in the last fifty years or so. As we all know, our sons and daughters understand more about the workings of PCs than I do. So you have actually a rather odd situation where transmission is almost going in the reverse direction, generally where in which we're sort of hastening to keep up with children who have acquired massive amounts of cultural information that wasn't available to us when we were their age.
On the missing link between genes and cultural information:
We know obviously that genes build bodies, and we know that they build brains and the kind of brains we have are very, very interesting and unusual for a primate. And one of the main things that we're able to do that we suspect others aren't is to engage in representational thought. In other words, we can use symbols. We can use written symbols, we can use language - spoken language itself is a symbol - we can use mathematics which is a particular symbolic form. Because we're able to do that, it absolutely explodes massively, the kinds of ideas, the kinds of inventions we can have, and of course the rate at which they can be spread around a society from one mind to another, and I think that's what makes humans very unique, and which makes this rapid period of evolution quite frightening in how these ideas are proliferated.
The Arguments: Dr Steve Jones
Professor Steve Jones is a geneticist at University College, London. He is the author of The Language of the Genes and other popular science publications. Professor Jones thinks that the relaxing of natural selection in the developed world and the fact that families these days have more or less the same number of offspring means that human evolution has effectively stopped.
On the idea that human evolution might have stopped:
"I really just know about snails, and the beauty of evolution is that it gives biology a structure, so the rules that apply to snails or to fruit flies to some extent apply to ourselves. Obviously there's much more that applies to us. But if you ask the simple Darwinian question about natural selection, inherited differences in the ability to pass on genes (which is only part of the evolutionary argument) it's pretty clear to me that at least for the time being and at least in the developed world, natural selection has stopped or at least slowed down."
On the essential features of an evolutionary system:
"Darwin phrased it very neatly with three words, 'descent with modification', and we can rephrase that even more neatly today with three other words shorter ones, 'genetics plus time', and it's got a couple of components very straight forward. Evolution isn't really biology, it's almost physics. If you've got a system which is based on information, and it copies that information from one generation to the next, and if that process of copying isn't perfect, which certainly DNA copying is not perfect, then you will certainly have evolution, that's inevitable. As Steven Rose says, really you can't disbelieve in it. Darwin's great contribution was to realise that what's actually changing is itself a copying machine, so that some of the new versions are better at copying themselves, and those new versions are spread, and that's natural selection, and that really is all that evolution is in its basics."
On the creationist argument:
"Well if we were talking about astronomy, we wouldn't be sitting learnedly asking whether the earth was flat or not, because we know the earth isn't flat. There are a few cranks who might believe that it is, but it's a waste of your time, my time and the audience's time to discuss it, and I feel exactly the same about the creationist argument."
On the idea that there is a mechanism for transmitting cultural ideas from one individual across generations:
"As an experimental scientist, I do experiments of things which I can manipulate which are experiments for snails, experiments with fruit flies, DNA and so on, and I can map out genes, I can work out the history of population movements and that kind of stuff, exactly the kind of things that Darwin was doing. He didn't have a DNA machine, but he was a very good comparative anatomist, which is basically doing the same kind of thing. And really both Darwin and his very minor disciples like myself, manage to do all that without using universe. Evolution is often used as a kind of universal metaphor, and that's a real danger. I'm often reminded of the fact, not many people know this, that the United States' Constitution with the President and House of Representatives and the Senate and the like, was actually designed as a model of the universe, of the solar system. There should be a sun in the centre, and a certain distance away there should be planets, and around each planet there should be a few moons. Now that was a scientific decision as how to design your constitution. As it happened it worked pretty well, reasonably well. But the idea that we should design our way of life because of the way the universe is, everybody would laugh at. I rather think the same about us saying that we should understand our way of thought, our language, our culture, because of Darwinian natural selection, is really just a shallow."
The Arguments: Professor Steven Rose
Professor Steven Rose is Professor of Biology and Director of the Brain and Behaviour Research Group at the Open University, Joint Professor of Physics at Gresham College in London and visiting Professor, Department of Anatomy and Developmental Biology at University College London
On his area of interest:
"Well I'm a neuroscientist and interested therefore in behaviour, but as a biologist I'm interested in evolution. Evolution simply means change over time, changing species, changing populations, change in the characteristics of individuals in a species. In that sense it actually can't stop, and in that sense it's not a theory, it's a fact. The theoretical issues are the motors of evolution, if you like."
On the questions about evolution that divide biologists:
"I think we can remove the creationist argument from this discussion, and then we can get to the interesting questions, which do divide biologists. The debates within biology I think focus on a number of features. One is whether evolution is only to be understood as a genetic mechanism in that sense. I mean there's a formal definition which some evolutionary biologists use as the rate of change of genetic frequency in a population, which says that what happens to organisms - you and I and the others of us in the audience - doesn't matter, it's only our genes that matter. Others would argue as I would, and Stephen Jay Gould would, that you have to see evolution acting at various levels on the gene, on the genome, on the organism, on the population, and on the species as a whole, and also, whether natural selection is the only motor of evolutionary change, or there are others as well. Anne talked about sexual selection, but there are other reasons and constraints on evolutionary change, which I think become very exciting for biologists to try to uncover."
On whether genes should be referred to as building bodies:
"I think one's just got to see that genes are strands of DNA. In order to build a body, you need the cell in which the gene is located, you need the genome in which the gene is there, and to give the genes this sort of master molecule metaphor, I think is to give them too much power, almost magical power, and as someone who started as a biochemist and cares about cells and metabolism, I feel uneasy when we rather glibly use that metaphor. I'm saying that genes are absolutely essential for the construction of brains but what the missing link was, was not just social and cultural history but also the developmental history of the organism which we construct ourselves, if you like, out of the raw material given by our genes and our environment - and if we miss development out, we're in deep trouble."
Steven Rose (Penguin Books 1998), ISBN: 0140237003
Alas Poor Darwin
Hilary Rose and Steven Rose (Vintage 2001), ISBN: 0099283190
Almost Like A Whale: The Origin of Species Updated
Steve Jones - hardback: Doubleday 1999, ISBN: 0385409850; paperback: Black Swan 2001, ISBN: 055299958X
The Language of the Genes
Steve Jones (Flamingo 2000), ISBN: 0006552439
The Theory of Evolution
John Maynard Smith (Editor), Richard Dawkins (Cambridge University Press 1993), ISBN: 0521451280
Climbing Mount Improbable
Richard Dawkins, Lalla Ward (Illustrator) (Penguin Books 1997), ISBN: 0140179186
The Cambridge Encyclopedia of Human Evolution
Steve Jones, Robert Martin, David Pilbeam, Sarah Bunney (Editor) and Richard Dawkins (Cambridge University Press 1994), ISBN: 0521467861
The Origin of Species
Charles Darwin (Prometheus Books UK 1994), ISBN: 0879756756
The Structure of Evolutionary Theory
Stephen Jay Gould (Belknap Press 2002), ISBN: 0674006135
- Someone who researches and studies natural history, botany and zoology
- An organised being; a living body, either vegetable or animal, composed of different organs or parts with functions which are separate, but mutually dependent, and essential to the life of the individual.
- The science which studies of the phenomena of living organisms; the study of the processes incidental to, and characteristic of, life. It is divided into animal and vegetable physiology, dealing with animal and vegetable life respectively. When applied especially to a study of the organs and tissues in man, it is called human physiology.
- The total number of people or organisms in a specific area.
- Spontaneous generation
- Or abiogenesis, is the idea that life, rather than evolving over many millions of years from the primordial soup, was started by an outside factor - some theories suggest it was seeded by extraterrestrial impact from an asteroid impact.