Some Thoughts on “Adaptive Peaks,” “Dobzhansky’s Dilemma”—and How to Think About Evolution

Theodosius Dobzhansky was one of the most important evolutionary biologists of the twentieth century. Born in Russia in 1900, Dobzhansky came to Columbia University in New York in late 1927 to work in Thomas Hunt Morgan’s famous “fly room”—birthplace of much of modern genetics. He had been trained as a systematist, with an expertise on ladybird beetles. Dobzhansky’s (1937) first book—Genetics and the Origin of Species—was in many ways his best. The book went through two subsequent editions (1941, 1951), expanding and clarifying his own evolving thought. When it came time for a fourth edition, Dobzhansky’s equally renowned colleague Ernst Mayr (personal communication) pleaded with Dobzhansky to change the title—which he did— to Genetics of the Evolutionary Process (1970). Excellent as all these works were, though, there is something that still seems fresh as one reads that first book (1937)—where Dobzhansky wrestled for the first time in an extended format with problems of reconciling the genetics of populations with the Darwinian vision of evolution through natural selection. I remember Dobzhansky’s 1937 work primarily for three reasons—three areas of discussion of evolutionary processes which were novel, even perhaps revolutionary at the time he was writing. First, he was thinking in hierarchical terms: Dobzhansky made it explicitly clear that the rules governing genetic inheritance (“physiological genetics” in his parlance) are different from the rules governing the fate of gene frequencies within populations (“population genetics”). Selection and drift occur in populations, at least in large measure independent of mutation and the mechanics of parent–offspring inheritance. He also saw that the smoothly continuous states of genetic variation within populations stand in contrast to discrete states of alleles–mutations at the individual level and also in contrast with the manifest genetic discontinuities between discrete, yet closely related, species. Secondly, Dobzhansky was the first to rethink the importance of geography in setting up the discontinuities between species. Though Mayr (1942) is largely remembered for elaborating the concept of allopatric speciation (see Thanukos 2008, for a review), in reality, it was Dobzhansky who had first resurrected the importance of isolation (primarily geographically induced) in speciation and thus to the evolutionary process in general. But, thirdly, Dobzhansky was concerned with the maintenance—and selective value—of genetic variation in natural populations. He had become enamored with Sewall Wright’s (e.g., 1931, 1932) imagery of the “adaptive landscape,” using it to frame his discussion of various evolutionary issues. Wright (born in 1889) was a geneticist based at the University of Chicago (and later at the University of Wisconsin) for most of his long, productive career. He was one of three geneticists (the other two being the Englishmen Ronald Fisher and J.B.S. Haldane) who applied their gifts with mathematics and statistical analysis to evolutionary genetics, essentially founding the field of “population genetics,” and effectively reconciling genetics with the Darwinian theory of evolution through natural selection. Sewall Wright is perhaps best remembered for his notion of “genetic drift.” He demonstrated mathematically that genes could “go to fixation” (i.e., not be eliminated by Evo Edu Outreach (2008) 1:243–246 DOI 10.1007/s12052-008-0057-4