An excellent review of modern work on ancient DNA and its significance to human history. Most of the work discussed was done in the author's laboratory. The author is clear, but he is the head guy, not a science journalist like Carl Zimmer, and he cannot or will not elaborate on or repeat his explanations. I don't think anybody would expect a detailed explanation of principal component analysis in a work like this, for example, and some concepts like the four population test are greatly enhanced by good diagrams, but when Professor Reich points out a situation where frequent mutations are uncommon and infrequent ones are common, I found simple re-reading to be inadequate. In a final discussion of the significance of the newly discovered features and likely yet to be discovered features of our genomes on the concept of race, the author refreshingly says,
If we aspire to treat all individuals with respect regardless of the extraordinary differences that exist among individuals within a population, it should not be so much more of an effort to accommodate the smaller but still significant average differences across populations.