How the Snake Lost Its Legs the butterfly, the snake, and the cheetah. Each consists of three to eight sections named in the style of Rudyard Kipling's "Just So Stories", with titles like "How the butterfly got its spots" or "How the snake elongated its body", though a couple of sections use "Why?" rather than "How?", as in "Why the fly twirls his penis" (it rotates during embryonic development under the control of different genes). In these chapters, Held explains the mechanics of evolutionary developmental biology, complete with accounts of what genes such as hox, hedgehog, and engrailed do to shape bodies. The third part is
Who We Are and How We Got Here criticised for its writing style and its handling of race, though other reviewers observe that nothing it says should give racists any comfort. David Reich is a geneticist who has studied ancient human genomes, comparing their patterns of mutations to discover which populations migrated and mixed throughout prehistory. He was mentored by the population geneticist Luca Cavalli-Sforza, who from 1960 pioneered the attempt to match the study of human prehistory by archaeology and linguistics, using the limited genetic data available at that time. "Who We Are and How We Got Here" was published by Oxford University Press in 2018, .