Adaptive evolution is an ongoing process, and can result in interesting changes over historical time – and it has, because the human race, most of it, has been experiencing drastically different environments in recent millennia, environments that are largely the products of our own crazed imaginations.
You’d think that anthropologists, historians, and sociologists would be fascinated by these new vistas opened up by modern genetic technology, but of course they’re not. Either they pay no attention or they promulgate reassuring nonsense about how people haven’t really changed. (“They’re still just a bunch of rats”).
The hell with them all.
Now that I’ve gotten that off my chest, one of those subjects that people ought to be excitedly exploring is caste, the nutty social system in India.
As Wiki puts it, “Indian society has consisted of thousands of endogamous clans and groups called jatis since ancient times.” And we know that: the genetic evidence indicates that many of the major castes have been highly endogamous for about three thousand years.
This has implications. An endogamous group that is exposed to unusual selective pressures – say because of their occupation – is going to change in response to those particular selective pressures. That is not the case in a society that mixes fairly freely, one in which smiths marry farmers’ daughters and the daughters of clerks marry shoemakers. In that case, the only selective pressures that result in much change have to affect a major fraction of the population, often everybody – as with adaptation to new foods or new communicable diseases.
If the endogamous group isn’t too big (which often seems to be the case), you’ll see genetic drift. There should be lots of jati-specific genetic diseases in India, if this picture is correct. Which should result in a torrent of interesting medical-genetics papers out of Indian, but I don’t believe that is actually happening.
The third point, which I’ve mentioned before, is that a population made up of a zillion little endogamous groups should slow the spread of selective sweeps.
By contrast, places like Europe (that has had only two small endogamous occupational castes, Jews and Gypsies) should have no specialized occupational adaptations (except maybe for farming), little drift, and a more rapid spread of selective sweeps. Selection on standing variation should work at about the same speed in an endogamous or open group, except that it would respond to general selective pressures in the open group and caste-specific selective pressures in the Indian-like population.