> 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.

We are all mixed race.

https://www.goodreads.com/en/book/show/35749414-who-we-are-a...

By DNA there is rarely any non-mixed population of ethnic groups. That applies both to maternal(unless interbreeding is a preference) and paternal lineages, as people are quite mixed, but borders of cultures and beliefs(in various myths - including about their ancestry) is what is holding societies together.

By appearance admixture is the one that defines looks and that includes racial look and it is question of mere 3 generations for descendants to look like anyone else around them, as that is where admixture differences are washed out. USA has a lot of issues in this matter, like with "one blood drop rule" that is still used in definitions of races and also cultural war issue, which is affecting rest of the world in these matters not to mention taboo subject of races.

"race" is not a concept that's really supported by genetics [1]

[1] https://ewanbirney.com/2019/10/race-genetics-and-pseudoscien...