Suppose we look at two very similar cities, one populated by whites and one populated by whites, blacks, and Mexicans. Wouldn’t it be interesting if the heights of the white people in the diverse city were more closely huddled around the white mean?
Here’s how I figure: in diverse areas, people are more likely to behave according to their ethnic stereotypes because this conformity is policed by their tribal in-group. Every tribe is a little bit on edge because at any moment one of the races might get the upper hand and drive the others out. So it’s important to everyone to make sure their fellow ethnics immediately know which side they’re on when the chips are down, with no hesitations. Therefore less deviation in personality is allowed because in the main behavioral conformity shows strong emotional investment in one’s identity and therefore greater loyalty. So the behavior policing is just loyalty compliance testing.
Well, we don’t understand very well what effect the environment can have on genes either at conception or epigenetically during development. But if it has any at all, wouldn’t we expect this particular environment to cause less varied genetic expression? Like I said, that would be very interesting. Presuming reasonable nutrition, height would be a good proxy test for that.
One problem with this is that ethnic tension doesn’t show up as much when the economy is doing well and everybody’s fat and happy. But when times are tough there’s a lot more resentment and tension- and this is also when we’d expect people not to be eating as well.