says physicist Steve Hsu in commenting on a particularly smug and fatuous posting by economist Brad DeLong. Following Bruce T. Lahn's discovery of two brain development genes that are distributed to quite different degrees around the world, the Berkeley economist wrote:
Ongoing Human Evolution
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 ...
And Dr. DeLong is off to the mathematical races. The only problem is that he didn't bother reading the NYT article Sullivan linked to showing that in the case of these two brain genes, the human gene pool is not well-mixed.
For these genes (and a lot of other ones) there have either been stronger barriers to intermating among racial groups (e.g., oceans) than DeLong assumes or that there were different selection pressures in different regions (e.g., lactose tolerance was selected for in Northern Europe but not in South America before 1492 because Amerindians didn't milk animals), or both.
DeLong's confidence in his his non-factual assumption reminds me of the classic joke:
A physicist, a chemist, and an economist are shipwrecked on a desert island. Starving, they find a case of canned pork and beans on the beach, but they have no can opener. So, they hold a symposium on how to open the cans. The physicist goes first:
"I've devised a physical solution. We find a pointed rock and propel it at the lid of the can at, say, 25 meters per second --"
The chemist breaks in:
"No, I have a chemical solution: we heat the molecules of the contents to over 100 degrees Centigrade until the pressure builds to --"
The economist, condescension dripping from his voice, interrupts:
"Gentlemen, gentlemen, I have a much more elegant solution. Assume we have a can opener..."