• DOI:10.1086/284983
• Corpus ID: 84541831

Speciational Trends and the Role of Species in Macroevolution

@article{Futuyma1989SpeciationalTA,
  title={Speciational Trends and the Role of Species in Macroevolution},
  author={Douglas J. Futuyma},
  journal={The American Naturalist},
  year={1989},
  volume={134},
  pages={318 - 321}
}

• D. Futuyma
• Published 1 August 1989
• Biology
• The American Naturalist

Professor Grant (1989) argued that in my recent note on the role of species in anagenesis (Futuyma 1987), I have independently discovered his principle of "speciational trends," and he noted the failure of younger authors to cite precedents in the older literature for their ideas. Although I strongly advocate a historical perspective on one's field and attempt to live up to this ideal, I must admit to overlooking some points of similarity between Grant's ideas and my own, although I was familiar with his original statement on the subject (1963). In my defense, however, I wish to point out important differences in emphasis. One may distinguish in evolutionary genetics two traditions that may be termed Fisherian and Wrightian. The Fisherian tradition emphasizes additive gene action and the relatively unconstrained response of populations to selection (given genetic variation). The Wrightian tradition emphasizes the importance of genetic integration by phenomena such as pleiotropy and gene interaction (epistasis). This theme, although relatively muted throughout the 1970s and early 1980s, was championed by Dobzhansky (partly through Wright's influence; Provine 1986) and his students (e.g., Wallace 1968; Lewontin 1974), as well as by Mayr (e.g., 1963) and by Grant (1963, 1977). It is in this framework that genetic constraints may be invoked to explain stasis, and in which reduction in population size, by enabling drift-induced peak shifts, may facilitate rapid evolution and speciation; thus, it is this tradition that gave birth to the concept of punctuated equilibrium (Eldredge and Gould 1972). Population geneticists who have criticized punctuated equilibrium (and sometimes the peripatric speciation model of Mayr, on which it is based; see, e.g., Barton and Charlesworth 1984) do so in part because of a belief in relatively unconstrained responses of populations to selection. That is, they tend to accept Fisherian assumptions to a considerable degree. Although I believe the importance of epistasis and other genetic constraints remains an open question, the capacity of populations to respond to selection appears great enough to have led me to propose a hypothesis that, by granting free responses to local selection pressures, should be palatable to even an extreme Fisherian. My hypothesis nevertheless can explain such stasis and such association of morphological change with speciation as the fossil record may reveal. In my note, I hypothesized that even for entirely additively inherited polygenic characters, speciation, although not facilitating adaptive change in the sense of enabling gene-frequency change that would otherwise fail to occur, would confer permanence on adaptive changes by preventing recombination with other popula-