The late German-American biologist Ernst Mayr (1904-2005) was a leading light in the field of evolutionary biology, gaining a PhD at the age of 21. He was also a tropical explorer and ornithologist who undertook an expedition to New Guinea and collected several thousand bird skins. In 1931 he accepted a curatorial position at the American Museum of Natural History. During his time at the museum, aged 37, he published his seminal work 'Systematics and Origin of the Species' which integrated the theories of Darwin and Mendel and is considered one of his greatest works.
Darwin was always accused of having introduced evolution by chance, and it was… he was accused with the words, ‘How can you explain the evolution of such a perfect organ as the eye by chance?’ These people – and this included even many geneticists – did not realize that natural selection is a two-step process. The first step consists of the production of variation, an immense amount of variation, and also as I showed in my 1963 book, there are all sorts of mechanisms to preserve this variation as much as possible. And this variation, whether it is new mutations or recombinations, the breaking up of chromosomes during meiosis, any of the processes that lead to the meeting of different mates with different genotypes, all this is a matter of chance, there's no question about it. At the first step of natural selection chance reigns supreme. However, the next step, the survival of certain individuals while the majority are being eliminated by natural selection, this survival is not a matter of pure chance. This is a matter of certain individuals being actually fitter at that particular moment than others and therefore having a greater chance to survive than the ones that are less fit. And so, the second step of natural selection, which also includes a great deal of chance because a very favorable individual, for instance, might suddenly die in an accident… the philosophers always talk about the two identical twins in which one of them is killed by lightning, and the question is: is the one that was killed by lightning less fit than the other or not? And philosophers having a wonderful time arguing this point. But the point that I'm making is that even at the second step where the fitter individuals, the better adapted individuals, have a greater chance to survive, even there chance plays a considerable role. So you have two things: chance and selection, which you might call ‘necessity’, or you might call ‘design’ if you're a natural theologian, and it's the two work together. Now the old Greeks already… the Greek philosophers argued, what is it that makes the world change: is it chance or is it necessity, or is it accident or is it design? Well, the Darwinian solution is they both contribute to the changes in the world. The chance factor produces the variation that is needed by natural selection, and natural selection is the necessity factor which favors certain individual… or individuals over others. So if we look at natural selection in this new way, it is perfectly clear that all the criticisms of Darwin were quite… they were failures because they didn't take into consideration that natural selection is a two-step process with a very different load of chance in both parts of this process.
Walter J. Bock is Professor of Evolutionary Biology at Columbia University. He received his B.Sc. from Cornell and his M.A. and Ph.D. from Harvard. His research lies in the areas of organismal and evolutionary biology, with a special emphasis on functional and evolutionary morphology of the skeleto-muscular system, specifically the feeding apparatus of birds.