Darwin’s theory of evolution has become the bedrock of modern biology. But for most of the theory’s existence since 1859, even biologists have ignored or vigorously opposed it, in whole or in part.
It is a testament to Darwin’s extraordinary insight that it took almost a century for biologists to understand the essential correctness of his views.
Biologists quickly accepted the idea of evolution, but for decades they rejected natural selection, the mechanism Darwin proposed for the evolutionary process. Until the mid-20th century they largely ignored sexual selection, a special aspect of natural selection that Darwin proposed to account for male ornaments like the peacock’s tail.
And biologists are still arguing about group-level selection, the idea that natural selection can operate at the level of groups as well as on individuals. Darwin proposed group selection — or something like it; scholars differ as to what he meant — to account for castes in ant societies and morality in people.
How did Darwin come to be so in advance of his time? Why were biologists so slow to understand that Darwin had provided the correct answer on so many central issues? Historians of science have noted several distinctive features of Darwin’s approach to science that, besides genius, help account for his insights. They also point to several nonscientific criteria that stood as mental blocks in the way of biologists’ accepting Darwin’s ideas.
One of Darwin’s advantages was that he did not have to write grant proposals or publish 15 articles a year. He thought deeply about every detail of his theory for more than 20 years before publishing “On the Origin of Species” in 1859, and for 12 years more before its sequel, “The Descent of Man,” which explored how his theory applied to people.
He brought several intellectual virtues to the task at hand. Instead of brushing off objections to his theory, he thought about them obsessively until he had found a solution. Showy male ornaments, like the peacock’s tail, appeared hard to explain by natural selection because they seemed more of a handicap than an aid to survival. “The sight of a feather in a peacock’s tail, whenever I gaze at it, makes me sick,” Darwin wrote. But from worrying about this problem, he developed the idea of sexual selection, that females chose males with the best ornaments, and hence elegant peacocks have the most offspring.
Darwin also had the intellectual toughness to stick with the deeply discomfiting consequences of his theory, that natural selection has no goal or purpose. Alfred Wallace, who independently thought of natural selection, later lost faith in the power of the idea and turned to spiritualism to explain the human mind. “Darwin had the courage to face the implications of what he had done, but poor Wallace couldn’t bear it,” says William Provine, a historian at Cornell University. (Read commentary by Dr. Provine on passages from "On the Origin of Species." )
Darwin’s thinking about evolution was not only deep, but also very broad. He was interested in fossils, animal breeding, geographical distribution, anatomy and plants. “That very comprehensive view allowed him to see things that others perhaps didn’t,” says Robert J. Richards, a historian at the University of Chicago. “He was so sure of his central ideas — the transmutation of species and natural selection — that he had to find a way to make it all work together.” (Dr. Richards comments on "On the Origin of Species.")
From the perspective of 2009, Darwin’s principal ideas are substantially correct. He did not get everything right. Because he didn’t know about plate tectonics, Darwin’s comments on the distribution of species are not very useful. His theory of inheritance, since he had no knowledge of genes or DNA, is beside the point. But his central concepts of natural selection and sexual selection were correct. He also presented a form of group-level selection that was long dismissed but now has leading advocates like the biologists E. O. Wilson and David Sloan Wilson.
Not only was Darwin correct on the central premises of his theory, but in several other still open issues his views also seem quite likely to prevail. His idea of how new species form was long eclipsed by Ernst Mayr’s view that a reproductive barrier like a mountain forces a species to split. But a number of biologists are now returning to Darwin’s idea that speciation occurs most often through competition in open spaces, Dr. Richards says.
Darwin believed there was a continuity between humans and other species, which led him to think of human morality as related to the sympathy seen among social animals. This long-disdained idea was resurrected only recently by researchers like the primatologist Frans de Waal. Darwin “never felt that morality was our own invention, but was a product of evolution, a position we are now seeing grow in popularity under the influence of what we know about animal behavior,” Dr. de Waal says. “In fact, we’ve now returned to the original Darwinian position.”
It is somewhat remarkable that a man who died in 1882 should still be influencing discussion among biologists. It is perhaps equally strange that so many biologists failed for so many decades to accept ideas that Darwin expressed in clear and beautiful English
The rejection was in part because a substantial amount of science, including the two new fields of Mendelian genetics and population genetics, needed to be developed before other, more enticing mechanisms of selection could be excluded. But there were also a series of nonscientific considerations that affected biologists’ judgment.
In the 19th century, biologists accepted evolution, in part because it implied progress.
“The general idea of evolution, particularly if you took it to be progressive and purposeful, fitted the ideology of the age,” says Peter J. Bowler, a historian of science at Queen’s University, Belfast. But that made it all the harder to accept that something as purposeless as natural selection could be the shaping force of evolution. “On the Origin of Species” and its central idea were largely ignored and did not come back into vogue until the 1930s. By that time the population geneticist R. A. Fisher and others had shown that Mendelian genetics was compatible with the idea of natural selection working on small variations.
“If you think of the 150 years since the publication of ‘Origin of Species,’ it had half that time in the wilderness and half at the center, and even at the center it’s often been not more than marginal,” says Helena Cronin, a philosopher of science at the London School of Economics. “That’s a pretty comprehensive rejection of Darwin.” (Dr. Cronin’s comments on Darwin’s text.)
Darwin is still far from being fully accepted in sciences outside biology. “People say natural selection is O.K. for human bodies but not for brain or behavior,” Dr. Cronin says. “But making an exception for one species is to deny Darwin’s tenet of understanding all living things. This includes almost the whole of social studies — that’s quite an influential body that’s still rejecting Darwinism.”
The yearning to see purpose in evolution and the doubt that it really applied to people were two nonscientific criteria that led scientists to reject the essence of Darwin’s theory. A third, in terms of group selection, may be people’s tendency to think of themselves as individuals rather than as units of a group. “More and more I’m beginning to think about individualism as our own cultural bias that more or less explains why group selection was rejected so forcefully and why it is still so controversial,” says David Sloan Wilson, a biologist at Binghamton University.
Historians who are aware of the long eclipse endured by Darwin’s ideas perhaps have a clearer idea of his extraordinary contribution than do biologists, many of whom assume Darwin’s theory has always been seen to offer, as now, a grand explanatory framework for all biology. Dr. Richards, the University of Chicago historian, recalls that a biologist colleague “had occasion to read the ‘Origin’ for the first time — most biologists have never read the ‘Origin’ — because of a class he was teaching. We met on the street and he remarked, ‘You know, Bob, Darwin really knew a lot of biology.’ ”
Darwin knew a lot of biology: more than any of his contemporaries, more than a surprising number of his successors. From prolonged thought and study, he was able to intuit how evolution worked without having access to all the subsequent scientific knowledge that others required to be convinced of natural selection. He had the objectivity to put aside criteria with powerful emotional resonance, like the conviction that evolution should be purposeful. As a result, he saw deep into the strange workings of the evolutionary mechanism, an insight not really exceeded until a century after his great work of synthesis.