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June 20, 2004

Shy blue eyed boys

From Survival of the Prettiest (a data rich, if thematically somewhat unorganized, book), page 127 and 128:

[begin quote]
...psychologist Jerome Kagan has found that children with pale pigment, in particular children with blue eyes, are far more likely to be shy and inhibited than dark-eyed children. They are the most likely to be fearful of new situations, hesitant in approaching someone, quiet with a new person, and the most likely to stay close to their mothers. Brown-eyed children are bolder. Kagan speculates that fear of novelty, melanin production and corticorsteroid levels share some of the same genes.

His theory is speculative, suggesting that when people migrated to northern Europe they were faced with the problem of keeping up a body temperature that was used to a warmer climate. A mutation that increased the efficiency of the sympathetic nervous system and upped the level of norepinephrine...would have also raised the body temperature and offered a survival advantage. Unfortunately, it would have left them with a more reactive nervous system and a more timorous temperament. Where does the pigment come in? High levels of norepinephrine can inhibit the production of melanin in the iris and can increase the level of circulating glucosteroids that can inhibit melanin production as well. So blond hair and blue eyes and shyness may be a common biological package....
[end quote]

This seems an example of correlated response, the fitness cost of being extremely introverted in the northern European context is balanced in this case by other considerations (whether it be direct adaptation to the environment or sexual advantages). I would also not be surprised if in the EEA, where bands would be very large at 100 individuals (perhaps much smaller in Ice Age Europe) and inter-tribal interactions might have been rare, the relative fitness cost of being shy around "strangers" would have been much smaller, since there was little possibility of building large social networks which one could use to enhance social status, ergo, reproductive success. Contrast this with the "modern" context, attested to in books like The Tipping Point, where "connectors" can serve as nodes for social networks on the order of thousands of individuals, and parlay their gregariousness into careers in sales or leadership positions in business or government. I will make a tentative prediction that populations with a longer history of dense living & complex social structures [agriculture, urbanism] will have a smaller proportion of "shy" individuals.

In any case, the book above was published in 2000, so the author did not write with knowledge of the recent work that suggests northern peoples have a cold adapted metabolism. For those curious, here is Kagan's original article (he seems not to have fleshed out his theory much at this point), and a follow-up by another researcher that suggests that only blue-eyed males are particularly shy (blue-eyed females showing no difference). The above studies seem to have had samples composed of peoples of European ancestry, so one need not presume that brown-eyed Japanese are on average more outgoing than blue-eyed Swedes.

Posted by razib at 02:19 PM