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Health

I think Stephen Jay Gould would be appalled

Gene ExpressionBy Razib KhanJuly 25, 2006 7:35 AM

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I am a little unsure whether this article in The Washington Post titled And the Evolutionary Beat Goes On . . ., beginning with the sentence "Stephen Jay Gould would have been pleased," is a subtle joke or not. The journalist has a science background, and has even covered the evolution "controversy," but that doesn't really prepare you to dive into the brand new world of evolutionary genomics. Here is the short of it. First, biases on the table, to say that I am not a Gouldian is charitable. I would argue that evidence of recent human evolution and diversification seems to be positively un-Gouldian. Here is the Wiki summary of Gould's ideas in Gould's words:

A new species can arise when a small segment of the ancestral population is isolated at the periphery of the ancestral range. Large, stable central populations exert a strong homogenizing influence. New and favorable mutations are diluted by the sheer bulk of the population through which they must spread. They may build slowly in frequency, but changing environments usually cancel their selective value long before they reach fixation. Thus, phyletic transformation in large populations should be very rare-as the fossil record proclaims. But small, peripherally isolated groups are cut off from their parental stock. They live as tiny populations in geographic corners of the ancestral range. Selective pressures are usually intense because peripheries mark the edge of ecological tolerance for ancestral forms. Favorable variations spread quickly. Small peripheral isolates are a laboratory of evolutionary change.

As the Pritchard suggests Gould's work is somewhat orthogonal to what he and Lahn are studying, in sum Gould was focused on meta-taxa level macroevolutionary patterns and trends, while the human evolutionary genomics that is being reported is more species level and microevolutionary. But Gould's dismissal of the power of alleles to sweep to fixation within large populations via deme-to-deme networks seems wrong, or at least the skepticism should be mitigated (selection coefficients are nasty little things and I am not positing a world of "Ideal gas laws" a la Fisher). Additionally, the evolution that Lahn and Pritchard are detecting is happening at the center of the action of our species' range, not in small isolated populations. My understanding is that Gould emphasized the power of stabilizing selection in large populations, but stabilizing is not how you would describe the dynamics that are coming out of evolutionary genomics, the rate of change and the directionality are explosive and almost chaotic, scaling adaptive landscapes and shooting into multiple dimensions. Additionally, Gould was most definitely not a "selectionist," if that means anything, but the article mentions selection nearly a dozen times! From a Gouldian perspective we as a species are most definitely not in stasis, we're a missle of allele frequencies dancing through gene space. If you want to view it through a macroevolutionary lens we were on the cusp of speciating! Because of transcontinental travel that is probably not going to happen, at least for now (population to population gene transfer has a way of quickly blocking differentiation of coadapted gene complexes). But the big elephant in the room is that the possibility that evolution has been "adapting different groups to the particulars of their ecological niches" renders Gould's assertion that "Human Equality Is a Contingent Fact of History" moot. Physical equality implies equivalence, but human populations are not equivalent in their adaptiveness to various environments. This is why I have focused on The Andaman Islanders, these people render the perception of similarity shockingly deceptive, in particular because this population seems to die in the presence of Eurasians who blithely transmit their "super bugs" to them. Gould was wrong, the future does not belong to small isolated populations buffeted by stochastic contingency, it seems that the mass action of mutations driven by positive selection at the demographic center is where we should look. Postscript: If you want to know what Lahn and Pritchard are doing, you need to survey to W.D. Hamilton, R.A. Fisher and Sewall Wright's work. Much of recent human evolution seems driven by immune response, likely in a "Red Queen" manner as conceived by Hamilton. Additionally, the power of large populations to make drift less important and generate new mutations is a Fisherian insight. Finally, as the next level of granularity in this work proceeds I believe you will see some of the importance of substructure in a manner that Sewall Wright would have recognized. Gould's project was to bring paleontology to an equal footing with genetics in the study of evolutionary science, but evolutionary genomics brings empirical wealth which can be viewed through a classical theoretical population genetic lens.

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