Challenge to evolutionary psychology: What if the number of human ancestors is actually small?

Evolutionary psychology—the theory that human nature can best be understood by trying to guess the survival strategies that benefited human ancestors hundreds of thousands of years ago (and are now governed by our genes)—burst on the scene in the 1990s. after the controversial failures of similar trends in psychology, Social Darwinism and sociobiology.

Evolutionary psychology is an effort to bring social sciences into line with a current interpretation of Darwinian evolution favored by, for example, Richard Dawkins , by reducing the complex vagaries and choices of current human behaviour to simple formulas based on comparisons with primate apes and speculations about human prehistory based on chance findings from genome maps.

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Another serious practical problem for evolutionary psychology is that the number of common human ancestors may actually be quite small. ...

Why is this a problem? Because evolutionary psychology is, in general, group psychology. If the basic evolutionary psychology thesis were sound, a group would respond to a given issue (selective baby-killing, polygamy) by making choices that affects the group's survival and reproduction. This response is alleged to be encoded in our genes, turning up later in our thoughts.

But if only a few human beings are actually ancestors, only a few unique and unpredictable individual responses matter. It is no use theorizing about how early humans in general might have reacted if the individual who chooses to go against the group becomes the ancestor. And we don't even know, for mosst purposes, whether a decision that went against the group played any role in that individual's becoming an ancestor.
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