Ah. Andrew Sullivan looks forward--a little too eagerly?--to the division of the human race into subspecies along racial lines:
www.AndrewSullivan.com - Daily Dish: Humans are still evolving - and at quite a brisk pace, according to new research. Bad news for liberals: at the rate research is going, you will soon have to choose between believing in evolution and denying any subtle, genetic differences between broad racial groups.
He is, of course, wrong. He hasn't done the math. The human gene pool will be well-mixed as long as there is even a very small amount of cross-population genetic mixing.
To see this, let's suppose that you have two groups of humans--population 1 and population 2--that are almost completely separated: only one in a thousand marriages crosses group lines. And let's suppose that there is a highly favorable dominant mutation--one that increases the holder's relative chances of surviving to reproduce by five percent. Let's make 20 years be a generation. And let's further suppose that this mutation has spread so that 1% of the people in population 1 possess the mutation, and nobody in population 2 possesses it.
Now turn this situation loose. What will happen over time?
There will be an age--about 1500 years--in which a few people in population 1 have this mutation, and almost nobody in population 2 has it. There will be an age--about 750 years--in which about half of the people in population 1 have this mutation, and a few people in population 2 have it. There will be an age--about another 750 years--in which it is rare that somebody in population 1 doesn't have this mutation, and in which less than half of population 2 has it. There will be an age--another 1500 years--in which effectively everybody in population 1 has this mutation, and more than half but not yet effectively everybody in population 2 has it.
There is no age in which you can say what Andrew Sullivan wants to say: that there are subtle, genetic differences between "broad racial groups" in the sense that members of population 1 have the mutation, and members of population 2 do not.
There is surely enough mixing in the human gene pool today to prevent any future strong segregation of genetic markers by groups even as strong as what we see today with the epicanthal fold. Even today, I guess that my children's ancestors 750 years ago lived in what is now the United States, Ireland, Scotland, Wales, England, Germany, Belgium, France, the Netherlands, Spain, Portugal, Madeira, somewhere in West Africa, Italy, Sicily, Poland, Lithuania, White Russia, Ukraine, Great Russia, and Mongolia--and more.
UPDATE: Comments closed--I don't have time to keep them a discussion rather than a food fight.