What I wanted to talk about is somewhat of a parallel of that in human populations. If you were to go to a textbook on human biology from the time of Darwin or a bit later, you would certainly get an image that looked a bit like this. This is an image of the so-called races of humankind—racial types, as they called them. I’m not going to go into the question of whether there are real races of humankind because there aren’t. It’s interesting to note that until quite recently people assumed, and scientists assumed too, that the human species was divided into distinct groups that were biologically different from each other and had been isolated from each other for a long, long time.

Well, to some extent that was true. Until quite recently, human populations were isolated from each other. That’s changing quite quickly. ...