One of the dynamics which is always operative in evolutionary biology is adaptation through natural selection. We know that it happens in humans, and it is clear that it has happened in the past and is happening in the present. It’s most obvious when it comes to disease. You can see the spread of malaria adaptations in the New World, for example, and that’s clearly due to strong natural selection.
But it’s not just disease. A few years ago I noticed that ancient DNA was detecting evidence of rather recent depigmentation across Northern Europe. This is not to say that the general features of the phenotype in Northern Europeans were not mostly there by the Bronze Age. The Beaker People in Britain don’t seem that much different from modern British people.
Nevertheless, using the genomic resources now available to us, a few years ago researchers developed methods looking deep in the genome and found evidence of selection in English populations over the last few thousand years. One of those characteristics was pigmentation. Using similar methods, the Estonian group has found something similar, Differences in local population history at the finest level: the case of the Estonian population, has found something similar:
Another SNP from this list, rs7114857, lies within the GRM5 gene which has been shown previously to be a potential target of natural selection for the pigmentation phenotype . See Supplementary text 5.4 for details.
If you look at my post above, it’s pretty clear Baltic populations were pretty fair-skinned 3,000 years ago. But, these are the fairest populations in the world. And, it looks like that both ancient DNA and “best-of-breed” selection detection methods like SDS are pointing to further allele frequency shifts on the margin.
The question is why? First, there are two issues
– Pigmentation alleles can be pleiotropic. Pigmentation may not be the target of selection.
– If it is the target, then the debate moves to sexual and natural selection.
Pigmentation is an easy trait to discern. There is surely lots of selection in and around disease. But what other traits? The paper points to bone density is one characteristic, and size seems to go up and down a lot.
It’s sad George Williams wasn’t around to see the 21st century renaissance of “adaptationism.”