December 23, 2005

Pathogen selection and evolutionary psychology

A new blog called "Dusk in Autumn" writes about the Wang and Moyzis paper on 1,800 genes that have been under different selection pressures in West Africa, East Asia, and Europe:

I'll emphasize a point Steve Sailer raised, which is that this is contra the assumption in Evolutionary Psychology (TM) that selection worked its stuff while our species was located in Africa, and more or less froze us in that state before various groups left, since natural selection hasn't had "enough time" to work on our brain within the ~50,000 years since. Most cultural differences are assumed to reflect differences in the local ecology -- that is, we're all born with mostly the same cognitive architecture, but depending on how this interacts during our lifetime with salient features of the environment, some groups could show a psychological or behavioral difference from others...

However, as is the problem with Jared Diamond's Guns, Germs, and Steel, the more one emphasizes long-lasting differences in the local ecology, the more they are implicitly arguing that the populations occupying these areas over time face different selection pressures, which would tend to introduce a greater genetic component into explaining why different populations differ, as they became adapted to their region...

When it comes to the brain, however, the psychological / behavioral equivalent of the Standard Social Model is assumed to account for population differences. However, way back in 1993 Steven Gangestad and David Buss published an article, "Pathogen prevalence and human mate preferences" (Ethology and Sociobiology, 14, 89-96), wherein they described how the degree to which nasty pathogens were present in the local ecology strongly correlated with the degree to which the people of that region placed an emphasis on physical attractiveness when selecting a mate, as documented by Buss' seminal 1989 cross-cultural survey of human mate preferences (Ctrl+F BBS)... Buss had already examined how much emphasis people in various cultures place on good looks when choosing a mate; each subject rated this from 0 to 4, with 4 being most important, and he took the mean of all subjects in a given culture. G&B then examined the correlation of this average with the prevalence of 6 or so nasty pathogens in the geographical areas studied in mate preferences study -- by nasty I mean something like malaria, whose post-Out-of-Africa pressure has resulted in vast group differences in sickle-cell anemia. The hypothesis was that those in more pathogen-ridden areas would place more emphasis on good looks since they are a reliable cue for good health & immune system, which are more crucial for survival in an area teeming with microscopic bugs ready to eat you up. Here's Buss' summary from another paper which is available online (under 2001, "Human Nature and Culture..."). G&B:

"found that cultural variation in the prevalence of pathogens was correlated +.71 with the average cultural importance placed on physical attractiveness in a potential mate, accounting for a virtually unprecedented 50% of the cultural variation (Gangestad & Buss, 1993). Assuming further tests confirm this hypothesis, cultural variation in a psychological variable, in this example, can be traced, in part, to variation in an important hazard of the local ecology" (p. 969; my emphasis).

Aha! So despite the wording here about local hazards and the abstract's claim that "the [universal] human mind contains many complex psychological mechanisms that are selectively activated, depending on cultural contexts" (my emphasis) -- this is actually an instance of the Baldwin Effect, whereby learned behaviors become progressively more "hard-wired," even if not completely so, in order to increase fitness. But as anticipated by Darwin the Second (aka William Hamilton), and as confirmed now by the Wang et al paper, nasty pathogens play a central role in the directions natural selection takes in human beings. Combine this with the great variation in pathogen prevalence between geographical regions plus the Baldwin Effect, and you get psychological group differences with substantial genetic components. As I recall from the G&B paper, the Finns and Zulus face a milder pathogen army and on average don't care much about how their partner looks, whereas the Bulgarians and Nigerians, respectively, are the reverse.

My published articles are archived at -- Steve Sailer

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