A lot of great science in progress

Who We Are and How We Got Here
by David Reich

Absolutely masterful--widely scoped--detailed--deep but not drowning. State of the research in human population DNA, but with many reminders that the subject is growing and changing so fast that it might be out of date in ten years. Mind you, it's not saying our current research is "wrong", it's just "in progress". There are many things we know now that we never knew before, but there are known unknowns yet to come.

I'd read a good bit before about the interbreeding with Neanderthal and Denisovians, so the early Homo Sapiens migrations section wasn't as exciting to me as it could have been.  But if you haven't, this is a good place ot start. But when he goes into detail about other populations, things get wild.

Take India. Due to the strong prohibitions of inbreeding outside the caste, or jati, and further strengthening of the system under British rule,

...many Indian groups today might be the product of population bottlenecks. These occur when relatively small numbers of individuals have many offspring and their descendants too have many offspring and remain genetically isolated from the people who surround them due to social or geographic barriers.

Looking at those, they found that they could measure how long ago the populations diverged, and,

One of the most striking we discovered was in the Vysya of the southern Indian state of Andhra Pradesh, a middle caste group of approximately five million people whose population bottleneck we could date (from the size of segments shared between individuals of the same population) to between three thousand and two thousand years ago.

It was surprising, and even shocking. Based on this and other evidence, they determined that the "institution of caste has been overwhelmingly important for millenia".

Toward the end of the book he has a good discussion of the dangers of ignoring "racial" differences--should be "population"--in favor of political correctness. Doing so can blind us to legitimate differences that might explain, for example, different reactions to drugs.

And a lot more throughout. Great book.