Extending the Modern Synthesis at the Molecular Level

Question eight for my students is designed to see if they have read and understood three papers that were assigned to them.

G. Ledyard Stebbins and Francisco Ayala wrote in 1981,

During the last decade no other issue has been more actively debated among evolutionists than the role of random drift. Molecular studies have shown that protein polymorphisms are pervasive in natural populations and that protein changes accompany the evolution of species. The neutrality theory of protein evolution proposes that evolution at the molecular level is largely due to random drift rather than being impelled by natural selection. But many evolutionists maintain that natural selection plays an essential role even at the molecular level. The “selectionist” and “neutralist” views of molecular evolution are competing hypotheses within the framework of the synthetic theory of evolution.

Why do they refer to “selectionist” and “neutralist” views “of molecular evolution”? Is there no debate over the role of random genetic drift except at the molecular level? Do you agree with Stebbins and Ayala that Neutral Theory and the role of random genetic drift are usually included in the description of the Modern Synthesis? Did Gould agree when he wrote his 1980 paper?

The quotation is from a paper published in response to Gould's famous Paleobioogy paper where he said that, "I have been reluctant to admit it—since beguiling is often forever—but if Mayr's characterization of the synthetic theory is accurate, then that theory, as a general proposition, is effectively dead, despite its persistence as textbook orthodoxy." (see Good Science Writers: Stephen Jay Gould for a description of what Gould thought of his own claim in 2002.) This paper is now available online. In the past, lots of people referred to it but never read it.

Gould responded to the Stebbins and Ayala paper in Gould (1982). The three papers illustrate the core of the debate over the Modern Synthesis and its possible extensions. I think it's fair to say that modern evolutionary theory has moved away from the hardened version of the 1960s but still not addressed some of the issues that Gould raised thirty years ago.

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[Photo Credit: Photograph of Stephen Jay Gould by Kathy Chapman from Lara Shirvinski at the Art Science Research Laboratory, New York (Wikipedia)]

Gould, S.J. (1980) Is a New and General Theory of Evolution Emerging? Paleobiology 6:119-130. [PDF]

Gould, S.J. (1982) Darwinism and the Expansion of Evolutionary Theory. Science 216:380-387. [PDF]

Stebbins, G.L. and Ayala, F.J. (1981) Is a new evolutionary synthesis necessary? Science, 213: 967-971. [PDF]