Reich’s book, Who We Are and How We Got Here, is really two books. The first is an exposition of his excellent work using ancient DNA to understand prehistory. The second is about the impact of advances in genetics on our understanding of social issues, such as various forms of inequality and racial differences. It’s not obvious why that second book was written. It’s not his specialty, and it’s far more controversial. Which for sure doesn’t bother me, but might not be a good thing for Reich. Nor is it as good a book. While saying true things that would, if properly understood by the usual gang of idiots, get him into serious trouble, the book is interspersed with non sequiturs, falsehoods, and unjust attacks on people who committed the deadly sin of prematurely coming to the same general conclusions he has. It’s possible that he felt the need to cloak his general line of thought with clouds of toxic squid ink. I don’t much care what his reasons were: I’m going to praise and explain when he’s right, argue with him when I think he’s wrong, kick him in the goolies when he’s being a prick.
There are a few places – not many – in which this book is behind the fast-moving wavefront of research in ancient DNA. I don’t think that this is in any way Reich’s fault – it’s an inevitable consequence of how books are cooked. If I mention some recent result that has somewhat changed our thinking on something he discusses, something that he couldn’t have incorporated due to publication delays, I’m not dissing him.
On the other hand, Reich has some systematically wrong ideas about standards of proof. DNA analysis can yield tremendous amounts of high-quality information. We’re looking at billions of bases. We can therefore, analyze things more closely, and be far more certain of some results, than we could in the past. But that doesn’t mean that lesser kinds of evidence can’t be useful, or that nobody knew anything about the subject before modern geneticists (like David Reich) looked at it. For example, Reich mentions recent genetic work that strongly supports the idea that the genetic potential for height is generally higher in northern Europeans than in southern Europeans, and that this differences is the product of natural selection over the past few thousand years. He implies that we didn’t really know this until recently. Well, I was already pretty sure that Swedes run taller than Sicilians – and that those differences were still there when both groups had plenty to eat, since the same trend is observed in the US of A, land of the fat. Since Seneca and Tacitus noticed the very same thing (Germans are bigger than Italians), it’s not completely new information. The genetic work has told us more: we now know that height is influenced by many alleles, each of which accounts for a small fraction of the variance – and we now know the identity of those alleles. As for the height difference being the product of natural selection – well, isn’t everything?