It’s not a significant part of genetic divergence. Humans also have a striking lack of genetic diversity in the first place, due to factors like a severe population bottleneck 2 Mya.

One of the races is “black”, but since most Africans are black, and all humans have African ancestry, the idea of coming up with a genetic basis for “blackness” is completely useless. It would be difficult to come up with some kind of genetic basis for that category that is somehow useful to science, somehow includes most black people, and somehow excludes most non-black people.

It is more useful to talk about genetics in terms of (recent) ancestry. Ancestry is reasonably useful for things like screening for genetic conditions. You want to screen for sickle-cell anemia? Recent African ancestry is a reasonable thing to look for; blackness is a poor proxy. Recall that skin pigmentation is more about what latitude your ancestors are from, and not about what specific part of the world they are from.

(I’ve used the term “African ancestry” to refer both to long-term ancestry and more recent ancestry here, I hope that the usage is clear from context.)

> One of the races is “black”, but since most Africans are black, and all humans have African ancestry, the idea of coming up with a genetic basis for “blackness” is completely useless.

Proves too much: the idea of coming up with a genetic basis for "fishness" is also now completely useless.

> Proves too much: the idea of coming up with a genetic basis for "fishness" is also now completely useless.

I mean, that’s a good analogy, the term “fish” is even worse than “race”. Fish is paraphyletic, just like “tree”. There’s also the colloquial sense of “fish”, which is even less clear.

"Fish" are one of the classic examples of a commonly-understood descriptor that has little to no scientific rigor. Another good one is "tree".

In casual speech, you can certainly look at an animal and say "this is a fish", or look at a plant and say "that is a tree", but if you actually start to look closer, you find that there's no clear way to define either of those terms that includes everything we think should belong in them, and also excludes everything we think shouldn't.

"Races" among humans are similarly hard to pin down by any kind of genetic taxonomy.

fish exist. trees exist. races exist. we have laws about overfishing, laws about cutting trees down, and laws protecting against racial discrimination and these laws largely work. the legal system has developed techniques for dealing with gray areas too.

science is for describing what is, and in detail, but science's failure to do that just means we need more science, not that we should quit and claim the above words have no meaning.