Sunday, June 22, 2008

Expel the 7R?   posted by Razib @ 6/22/2008 12:25:00 PM

Dan at Genetic Future, a great guy, has another DRD4 post up. He has reproduced a chart from an article in The Economist which shows a trend where a higher frequency of the 7R (ADHD correlated variant) is found in groups which have migrated a greater distance. He asks whether "the "novelty-seeking" behavior associated with ADD may have extended into a desire to explore new territories." My first thought was this: perhaps people with the 7R variant were more likely to be kicked out of the tribe or village because they couldn't/wouldn't conform. Certainly the chart seems to imply that stable populations hovering around the Malthusian limit probably aren't too congenial for nonconformists. This is the argument at the heart of books such as The Moral Consequences of Economic Growth and Age of Abundance, though obviously there wasn't a genetic perspective there.

In any case, I think there's going to be some interesting stuff coming out of this area correlating lifestyle with personality profiles. You might recall that in Farewell to Alms Greg Clark repeated the old truism that farmers tended not to be more affluent than hunter-gatherers, and in fact the balance of the data implies most hunter-gatherer and nomadic groups have a median physiological fitness that is greater than that among farmers as measured by size and nutrition as evidenced by enamel growth. The genius of farming is that it obviously increased the productivity per unit area in terms of calories and so supported larger populations (physiological fitness obviously does not translate into reproductive fitness always), but it seems to me that the less violent and risky nature of this lifestyle (famines notwithstanding) meant that there was also less room for the nonconformists on the margins. I've argued in the past in some ways theat modern individualistic Westerners have more in common with hunter-gatherers than with peasants in "traditional" societies in regards to their mores. I wonder if the need and necessity for straight-jacket social control in village life induced a powerful bout of purifying selection against 7R across much of Eurasia, a pressure that is only now being relaxed.

Addendum: The expulsion of male misfits is one of the accounts given of the founding of Greek colonies. Of course, it could simply be that the annalists used the argument that these men were misfits to get rid of them and they were actually economical marginals who were a burden upon the citizenry.

Update: I want to be clear here to note that I don't expect that all H & G societies would favor 7R more than farmers. Just that I think that the constraints of an agrarian lifestyle around the Malthusian limit would result in less tolerance of variance of behavior on the margins. The marginal slack for H & G groups I assume would be due to more frequent tribe-level extinctions, war and interpersonal violence, as well as localized ecological parameters which have a more direct impact on H & G peoples.

Related: DRD4 posts.