Indeed, some evolutionary psychologists have implied
that one should not expect there to be any important variation
in traits that have a history of selection. For example,
Tooby and Cosmides (1992) argued that “human genetic
variation . . . is overwhelmingly sequestered into functionally
superficial biochemical differences, leaving our complex
functional design universal and species typical” (p.
25). The reason invoked for this assertion is that natural
selection, which is a winnowing procedure, should, if there
are no counteracting forces, eventually remove all but the
highest-fitness variant at a particular locus (Fisher, 1930;
Tooby & Cosmides, 1990), especially because complex
adaptations are built by suites of genes whose overall
functioning tends to be disrupted by variation. Because of
the winnowing nature of selection, the existence of heritable
variation in a trait is argued to be evidence for a trait’s
not having been under natural selection: “Heritable variation
in a trait generally signals a lack of adaptive significance”
(Tooby & Cosmides, 1990, p. 38, italics in
original).
Indeed, some evolutionary psychologists have impliedthat one should not expect there to be any important variationin traits that have a history of selection. For example,Tooby and Cosmides (1992) argued that “human geneticvariation . . . is overwhelmingly sequestered into functionallysuperficial biochemical differences, leaving our complexfunctional design universal and species typical” (p.25). The reason invoked for this assertion is that naturalselection, which is a winnowing procedure, should, if thereare no counteracting forces, eventually remove all but thehighest-fitness variant at a particular locus (Fisher, 1930;Tooby & Cosmides, 1990), especially because complexadaptations are built by suites of genes whose overallfunctioning tends to be disrupted by variation. Because ofthe winnowing nature of selection, the existence of heritablevariation in a trait is argued to be evidence for a trait’snot having been under natural selection: “Heritable variationin a trait generally signals a lack of adaptive significance”(Tooby & Cosmides, 1990, p. 38, italics inoriginal).
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