Another "big questions" book provided by Dimond Library at the University Near Here. The author, David Reich, is down at Harvard Medical School, but don't hold that against him. He's a leading researcher in the field of "Ancient DNA", a field that's blossomed over the past few years. Basically: you dig up people from past millennia, extract some reasonably intact genetic material, feed it into some hairy industrial biochemical processors, feed the data output by that into some high-strength computational algorithms, and out comes information concerning just where your Dead Guy fits into humanity's family tree.
But one of Reich's lessons is that a "family tree" is not a particularly accurate metaphor for how the various offshoots of humanity developed through history. Instead, it's more like a latticework: the DNA shows that ancient humans were surprisingly mobile and also, um, familiar with the other folks they ran across.
And they weren't particular in their familiarity, either. As a result, one of Reich's specific findings is that today's non-African people have a significant amount of Neanderthal DNA lurking in their chromosomes. (Added hundreds of mediocre stand-up comics: "… which will not come as a surprise to my wife.")
So just in a relative eyeblink, DNA research has provided new insights into our ancestry. Reich explores not only the Neanderthal stuff, but also how DNA reveals more about how and when people got to their "native" lands; it's far from the simple stories you and I heard about in school. Chapter by chapter, he looks at Europeans, Native Americans, Africans, Australians, Asians.
It's not without controversy, and (for me) that's a little more interesting than the dry recitation of research results. You may have heard that some Native Americans are reluctant to let researchers analyze those ancient American bones found at burial sites. They claim ancestry; the major problem with that claim is that research indicates that, almost certainly, the "native" people buried at a site 10K years ago are not related to the "native" people living there today.
Later chapters dig (inevitably) into deeper controversies of "racism". Reich dissociates himself from extreme thoughts on both sides: the notions that race is a mere "social construct" can't be supported by DNA research. Nor that racial differences are restricted to superficial matters of skin color and gross physiognomy.
He also distances himself from any controversial claims on what may be termed "the other side". Specifically, he dislikes folks like Nicholas Wade (whose book I looked at back in 2014). Reich was one of the signatories of this anti-Wade letter back then.
Frankly, I think he protests overmuch.