Comment by majormajor

> I will grant that by some historic definitions you could consider many people mixed race as neighboring cultures combine. But there are still very large and distinctly separate ethnic groups like black, white, asian, etc.

Isn't this exactly what you'd expect? Historically travel between the more obvious-by-skin-color-and-features ethnically-different groups has been slow and hard with some exceptions.

So you'd expect to see the lines get erased first among groups that started out closest together, and that seems to match with Europe some and especially the US where the English/Irish/Italian/German/Spanish/etc flavors of "white" all frequently ended up in the same cities. You also see more broader mixes in the US since it's historically been more open for, and attractive to, the sort of immigration that would produce it than the "home" countries for many of those ethnicities.

Even when you have a diverse total population like in the US, you only get a few shots per generation for a person of background A to have kids with one of background B, so it's gonna be really really slow, even before factoring in cultural/political factors that have generally actively discouraged it (or made it illegal in living memory!). Even the mixing of white-European ethnicities was often quite controversial. But as it became more common most Americans lost the ability to even recognize the differences, since they were more subtle than "skin color."

Give it 400 years of affordable air travel and it could look very different in countries with historical or future high levels of in-migration.