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Health

Selection "vs." drift

Gene ExpressionBy Razib KhanJuly 6, 2007 8:34 PM

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Recently a few blogs I follow have been having a back and forth "debate" which seem to recapitulate in the most general sense the "selectionist vs. neutralist" debates of the 1970s. Three posts from p-ter: Do phenotypes evolve neutrally?More on adaptationFinal Thoughts on adaptation From Larry: Visible Mutations and Evolution by Natural SelectionRichard Dawkins on Visible Change and Adaptationism While RPM offers Whither Adaptation? There are two general responses I have to these sorts of debates. First, their relevance to the "post-genomic era" is something I would question. The arguments date from a time when Richard Lewontin and John Hubby's famous allyzome papers were hot stuff. More precisely, Motoo Kimura formulated Neutral Theory in part to grapple with and explain Lewton and Hubby's findings. This was a time when molecular evolution was a nascent field, and it had to face the predictable if less than noble resistance from researchers schooled in classical Mendelian empiricism which focused on visible phenotypic markers to trace the inheritance of genetic elements. In 2007 these sorts of resentments and historical grievances seem to be shadows. You have a field like molecular ecology which serves as a branch between the lab and field tribes within the biological sciences. Human genomics is now opening up the elucidation of the DNA sequences which underlay traits whose heritable dynamics were previously analyzed via quantitative genetic methodologies (e.g., skin color). I think we should be careful about expending excessive cognitive cycles on demarcation and lexical debates about which evolutionary parameter is "more important." There are enormous data sets that need to be worked on. While skirmishes over philosophical purity have both substantive and entertainment value, they shouldn't be the main attraction. Second, Larry seems conflate random genetic drift with stochasticity. This just isn't so, selection can be stochastic. On the fundamental level one might expect that the seemingly random walk processes which we perceive and reify as "drift" have deterministic proximate causes. Randomness simply emerges because of our ignorance of the underlying variables. In any case, if you read a paper such as The Probability of Duplicate Gene Preservation by Subfunctionalization, I think you'll agree that the old dichotomy needs to be updated to fully reflect the reality of evolutionary dynamics.

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