[giraffe_lady]

Humans originated in africa, and only a subset of our species genetic diversity ever left africa. So all immigration from "many places" still represents only a subset of the existing diversity.

There is also some immigration directly from africa, but that can only increase it to at most the same as exists there. Almost certainly somewhat less, in practice.

[roughly]

Interestingly, even within Africa, the human genome notably lacks variability, to a point where it’s hypothesized that there was a fairly severe population bottleneck at some time in the last couple hundred thousand years.

[myhf]

oh gee i wonder what that bottleneck could have been

cough mysterious 1:4:9 monolith cough

[rbanffy]

I don’t remember exactly where I read that, but from mitochondrial DNA it was calculated that at some point we were down to 50 or so individuals.

[livinginfear]

It's worth noting that this is not the only hypothesis for the origin of modern humans: https://en.wikipedia.org/wiki/Multiregional_origin_of_modern...

[astrange]

It's the only correct one though.

There is small amounts of "multiregionality" since some peoples are part Denisovan and most everyone is part Neanderthal, but it's not even a plurality in anyone we've ever found.

[INTPenis]

Thank you for the clear explanation.

I've heard that humans were at some point reduced to a very small number, like thousands of individuals.

So how did a few thousand individuals become such great genetic diversity? Does genetic diversity come from being isolated, instead of mingling with other migratory groups?

[neonnoodle]

Human genetic diversity on the whole is very, VERY low compared to other species. The superficial physical variation we associate with ethnic diversity (skin tone, nose shape, lip shape, hair color/texture, eye folds and angles) are genetically insignificant compared to their visual impact.