I direct people’s attention to the interesting new theory on the sociobiological front, via Greg Cochrane over at West Hunter. Several of his recent posts apply. (HT Steve Sailer)
The traditional view is that selective pressure acts to encourage progressively improved mutations, so that people with cool new genes outperform those with the same old tired washday genes. While not denying or contradicting that, Cochrane's evidence is that another type of selection is more powerful. We acquire nicks and dents (metaphor) in our genetic code over time – mutations that are essentially neutral, but might be slightly less efficient than optimum. We’ve all got them, and got lots of them. They accumulate over time, and absent selective pressure, a gradual diminution of functioning creeps up on us. Some folks, by law of averages, accumulate more. In normal circumstances, this is no problem – our functioning is good enough. But in times of crisis, when need for speed or need for cleverness goes from being a nice feature to a feeding or mating necessity, people with higher concentrations of genetic clutter get weeded out. There is evidence that warmer environments don't have so many sludge-eliminating crises, and slightly-shabby DNA accumulates more there. We're talking centuries, BTW, not single generations.
The survival value of general genetic shininess, in addition to sudden acquisitions of single magical improvements, seems intriguing to me.