Biologists quickly accepted the idea of evolution, but for decades rejected natural selection, the mechanism Darwin proposed for the evolutionary process.
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Until the mid-20th century, they largely ignored sexual selection, an aspect of natural selection that Darwin proposed to account for male ornaments such as 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 individuals. Darwin proposed something like it to account for castes in ant societies and morality in people—long dismissed but now advocated by biologists such as E.O. Wilson and David Sloan Wilson.
How did Darwin come to be so ahead of his time? Why were biologists so slow to understand that Darwin had provided the correct answer to so many central issues?
Darwin’s long, slow obsession
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 at least 20 years before publishing On the Origin of Species in 1859, and for 12 years before its sequel, The Descent of Man.
Instead of brushing off objections to his theory, he thought about them obsessively until he found a solution. The peacock’s tail appeared hard to explain by natural selection: It seemed more 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 it, he developed the idea of sexual selection.
Darwin, the courageous
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 and turned to spiritualism. “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.
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Darwin of the broad horizon
Darwin’s thinking was not only deep, but also 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.
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 such as primatologist Frans de Waal.
Actor Andy Harrison, who portrayed Charles Darwin at Westminster Abbey on 4 February, is seen talking to the media next to Darwin’s grave in London.
It is remarkable that a man who died in 1882 should still be influencing discussions 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 mechanisms of selection could be excluded. There were also non-scientific considerations that affected the judgement of biologists.
In the 19th century, biologists accepted evolution, in part because it implied progress. But that made it harder to accept something as purposeless as natural selection. On the Origin of Species and its central idea were largely ignored and did not come back into vogue till the 1930s. And Darwin is still far from fully accepted outside biology. “People say natural selection is OK for human bodies but not for (the) brain or behaviour,” says Helena Cronin, a philosopher of science at the London School of Economics. “This includes almost the whole of social studies: That’s quite an influential body that’s still rejecting Darwinism.”
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A third problem, 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.
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.
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. Richards 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.’”
©2009/THE NEW YORK TIMES
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