- It fails to understand culture itself as a wholly natural phenomenon, as physical in its basis in neural structure as genetics is in its basis in DNA.
- It therefore fails to appreciate that culture itself is susceptible to a general Darwinian process of natural selection (though different, obviously, in its mechanisms) -- and that, in adapting to environmental challenges and opportunities far more rapidly than biology, culture can not only come into conflict with biology but can be a source of biological selection pressure itself.
- And that failure in turn leads to an under-appreciation of the idea that the most important contribution of biological evolution to human environmental fitness has been to cede psychological and social ground to culture, precisely by reducing the role of instinct and other genetic factors on human behavior.
It's instructive to put social constructionism and evolutionary psychology side by side, actually, and then to see them both as twin expressions of an undercurrent of ideological/political struggle that's been a feature of the culture for a while now. The former is aptly characterized as a type of anti-essentialism, and the latter, more recent school (in its contemporary versions), as perhaps an anti-anti-essentialism -- with each, depending on its degree of politicization, repelling the other toward increasingly untenable extremes. But even in their weaker, less political versions, both these schools simply miss the most salient fact about culture: that it too, just like DNA, is embedded in the natural, physical world. So, contrary to social constructionism, cultural concepts are driven by the real, natural environment; and contrary to evolutionary psychology, cultural concepts are themselves the primary evolutionary response to that environment.
*Here's the Wikipedia article (a start, but badly written even by Wikipedia standards); here's an FAQ by one of the important names in the field; and here's a "Primer" by Cosmides and Toobey, the two at the start of the recent surge in interest.