In his book The Undercover Economist, Tim Harford draws an amusing contrast between himself and biologist E.O. Wilson to illustrate the principle of comparative advantage — Wilson may be the better economist, Harford says, but given all the various things they’re good at, it still makes sense for Wilson to write books about biology while Harford sticks to economics.
Perhaps, but it would also make sense for Harford to be a trifle more skeptical about biology. He says:
Reading biologist Edward O. Wilson, I discover that in a few dozen generations all human beings will be “the same,” in the sense that whether in London or Shanghai or Moscow or Lagos, the same racial mix would be found. Viewed differently, the variety of human beings would be unprecedented: as this process of racial mixing accelerates, “many more combinations of skin color, facial features, talents, and other traits influenced by genes are now arising than ever existed before.” (The footnote is to p. 304 of Wilson’s book Consilience.)
Why does Harford endorse the notion that the process of racial mixing is accelerating? It’s trivially true that someone can have children with a person of a different race rather more easily now than was possible when the only way to get from one continent to another was to walk or paddle. But does that mean a whole lot of people are going to do it (relative to the size of the population)? How likely is migration on a scale sufficient to homogenize the populations of Lagos and Shanghai? Or preferential intermarriage with the indigenous population rather than with one’s fellow migrants?
The offhand phrase, “a few dozen generations,” is a sign that the writer really couldn’t be bothered to sketch out a few numbers on the back of an envelope. How long is it? Depending on what the meaning of “a few” or “generation” is, around 1,000 years. That hasn’t been long enough to homogenize Paris and Berlin, let alone Iceland and Greece or Africa and China.
What is accelerating is the rate of human evolution that is driving the continental populations apart faster than migration is blending them back together. There will be many more combinations of traits influenced by genetics, as Wilson says, but the likely outcome will be populations that are more geographically distinctive rather than less so, as Harford assumes.