A recent paper in PNAS talks about the evolution of the Pygmies – or, more exactly, the Pygmy phenotype, because it seems to have happened independently in the Biaka Pygmies (west Africa) and the Batwa pygmies of Uganda. The two groups have different genetic mechanisms for being short. Their shortness really is genetic, of course. Pygmies are mixed, to a degree: the more Bantu ancestry they have, the taller they are. And although height really is affected by nutrition, Pygmies are about six standard deviations shorter: someone of normal potential height would have had to starve to death (twice!) to be that short, and there would be lots of other symptoms of malnutrition that Pygmies don’t have.
Still, there were those who thought otherwise, presumably because they’d stuck a crayon up their nose as a kid. Way up. Environment does matter!
I noticed an interesting comment on this in Science: Michael Balter said “scientists had not been sure to what extent Darwinian natural selection is actually responsible for the Pygmy body type and how many times it has arisen over the course of evolution.” The bit about how many times it had arisen is reasonable – that takes looking at the genotype to be sure, and indeed it has occurred five or more times (in Africa and Southeast Asia). But there was no reason to wonder whether those changes were a product of Darwinian natural selection: that was a sure bet. Not just because it has happened multiple times in similar rain-forest environments. Darwinian natural selection is always operating.
Natural selection is not an odd, unusual, poorly understood phenomenon like ball lighting. It is not something that last occurred 50 million years ago, like a kimberlite pipe eruption. And, of course, it applies to human behavioral traits, which are significantly heritable. Unless you think that the optimum mental phenotype (considering costs and payoffs) was the same in tropical hunter-gatherers, arctic hunter-gatherers, neolithic peasants, and medieval moneylenders (which would strongly suggest that you are an idiot), natural selection must have generated significant differences between populations. Differences whose consequences we see every day, and that have been copiously documented by psychometricians.
This notion that ongoing natural selection is not the default – that it only happens on national holidays or whatever – is fairly common among biologists. Obviously untrue, because you can’t even have things stay the same without ongoing selection – otherwise mutations and drift would gradually ruin everything. Only selection lets horseshoe crabs outlast mountain ranges.
Sure, some of this is because the topic of human psychological differences makes biologists upset, or threatens to impose unemployment and/or celibacy – but it also shows up in topics that don’t seem to have much emotional or political charge. I think that only a few biologists reject those unexciting examples of ongoing natural selection because of a realization that they logically imply other, controversial conclusions. They do have such implications, but I think that poorly understood neutral theory plays a bigger role.