Perspectives in Biology and Medicine

ON GENETICS, SOCIOLOGY, AND POLITICS THEODOSIUS DOBZHANSKY* Typological Thinking There is a habit ofthought perhaps as old as language itselfthat keeps getting in the way ofour understanding ofthe history and nature ofthe processes oflife. This is our tendency to think in terms ofstatic types. Of course, we must sort out into categories the overwhelming diversity of phenomenawe perceive and experience, andwe do so inwords like "man," "cat," or "dog." Such words do not refer to particular persons or animals but to abstract representatives ofmankind, cat-kind, and dog-kind. Also, such words emphasize differences between "kinds" as ifthere were rigid boundaries; they give no hint ofwhat the "kinds" may have in common. Nor do they take into account, or even suggest, the diversity within "kinds"—the diversity ofpersons, of cats, and of dogs. Nevertheless, man has long sought for ways to unify as well as classify this diversity—since long before Bronowski said, beautifully, that "science is nothing else than the search to discover unity in the wild variety of nature—or more exactly, in the variety ofour experience. Poetry, painting , the arts are in the same search, in Coleridge's phrase, for unity in variety. Each in its own way looks for likeness under the variety ofhuman experience." One tempting way to unify is to declare that the diversity and change are false appearances. Plato did so by his famous theory ofideas. He believed that God created eternal, unchangeable, and inconceivably beautiful prototypes, or ideas, ofMan, Horse, and even such mundane and inanimate objects as Bed and Table; that individual persons, horses, beds, and tables are only pale shadows oftheir respective ideas; that acquiring wis- * Professor, The Rockefeller University, New York 10021. This is an adaptation of a paper presented at the Wenner-Gren Symposium in Burg Wartenstein, September, 1964. It appeared in the February, 1968, issue ofSocial Education and is reprinted here with their permission. 544 Theodosius Dobzhansky · Genetics and Sociology Perspectives in Biology and Medicine · Summer 1968 dorn means "seeing" the ideaswhere formerly one saw only their shadows. Aristode assumed only one cosmic idea, which manifests itself in the visible world. He believed that nature's "purpose" was to realize the ideal form and that all animals were variants ofa single architectonic plan. For more than 2,000 years—up to the time of Darwin—the organic world was viewed either as Plato or as Aristotle saw it, within the Western World. Either way was compatible with believing that living, and even non-living, bodies constituted a "Great Chain ofBeing" that ranged from lesser to greater perfection. Leibniz in the seventeenth century and Bonnet in the eighteenth century felt satisfied that the Chain is single and uninterrupted . Bonnet saw it starting with fire and "finer matters," and extending through air, water, minerals, corals, truffles, plants, sea anemones, birds, ostriches, bats, quadrupeds, monkeys, and so to man. To Lamarck and to Geoffroy St. Hilaire in the nineteenth century, but not to their predecessors and contemporaries, the Great Chain implied evolution. Cuvier, dissenting, was ofcourse absolutely right that there is no single plan of body structure common to all animals. Still, the hypothesis that living organisms are manifestations of a limited number of basic types or ideas ofstructure was useful because it inspired studies on comparative anatomy and classification. There is no doubt that such data, though collected for another purpose, did help to furnish a base for the theory ofevolution. Such are some ofthe pre-Darwinian roots oftypological thinking. Their common quality is that they postulate, implicidy or explicidy, archetypes or ideal types. Populational Thinking The Darwin-Wallace theory of evolution shattered the basis of typological thinking over a century ago, but many biologists are still unaware ofthis profound implication. I agree with Mayr that "the replacement of typological thinking by population thinking is perhaps the greatest conceptual revolution that has taken place in biology." My only cavil is that Mayr's "has taken place" is overoptimistic, although I do believe that this conceptual revolution is well under way. It has proceeded so slowly because the difference between typological and populational thinking is as subde as it is profound, but also because habits of thought are at least...