Two articles on evolution in one evening? What is this, frickin’ Pharyngula? Anyway, the Economist has an interesting piece up on the possibility that selective pressure is responsible for a biological difference in intelligence between Ashkenazi Jews and, well, everyone else. Gregory Cochran, the author of the paper, is no stranger to controversy, having previously suggested that homosexuality is the product of an infection. I’m not touching that with a ten-foot-pole (though any curious reader who looks into it is encouraged to post a comment with more info), but his thesis on intelligence among Ashkenazim seems to be worth considering.

Essentially he’s suggesting that the set of genes that causes diseases such as Tay-Sachs, Gaucher's and Niemann-Pick – all of which strike Ashkenazi Jews more frequently than most other people – are also responsible for heightened intelligence. This is where Cochran still has some evidence to collect – he doesn’t yet have proof that the same allele is responsible for the genetic disorders as well as heightened intelligence. At the same time, Cochran’s proposal sounds strikingly like an interaction that we already know to be real: sickle cell anemia and malaria.

West Africans, and people of West African descent, are susceptible to a disease called sickle-cell anaemia that is virtually unknown elsewhere. The anaemia develops in those whose red blood cells contain a particular type of haemoglobin, the protein that carries oxygen. But the disease occurs only in those who have two copies of the gene for the disease-causing haemoglobin (one copy from each parent). Those who have only one copy have no symptoms. They are, however, protected against malaria, one of the biggest killers in that part of the world. Thus, the theory goes, the pressure to keep the sickle-cell gene in the population because of its malaria-protective effects balances the pressure to drive it out because of its anaemia-causing effects. It therefore persists without becoming ubiquitous.

The article goes on to explain Cochran’s historical argument for how the disease/intelligence genes might have been selected for among Ashkenazim. I wonder though, how strong of a selective pressure the conditions he discusses could actually exert on intelligence. We know that rapid evolution can occur in the face of very strong selective pressures (see ex. antibiotic resistant bacteria or pesticide resistance development among insects), but I don’t see Cochran’s proposed pressures as especially “strong,” especially in light of the relatively short period of time in question (1,200 years or so for a species with ~25 year generations = ~50 generations). Will the kooky Darwinists in the room please stand up and tell me whether I'm full of it or not?

Oh, and if you’d like to read the paper for yourself (I confess that I only skimmed parts of it) you can check it out here (PDF).