March 23, 2005

How Much of the Behavior of the South African Proletariat Can Sociobiology Explain?

More than zero but less than a third.

Sam Bowles and Dori Posel, "Genetic Relatedness predicts South African migrant workers' remittances to their families", Nature 434 (2005): 380--383 [Journal link]
Abstract: Inclusive fitness models predict many commonly observed behaviours: among humans, studies of within-household violence, the allocation of food and child care find that people favour those to whom they are more closely related. In some cases however, kin-altruism effects appear to be modest. Do individuals favour kin to the extent that kin-altruism models predict? Data on remittances sent by South African migrant workers to their rural households of origin allow an explicit test, to our knowledge the first of its kind for humans. Using estimates of the fitness benefits and costs associated with the remittance, the genetic relatedness of the migrant to the beneficiaries of the transfer, and their age- and sex-specific reproductive values, we estimate the level of remittance that maximizes the migrant worker's inclusive fitness. This is a much better predictor of observed remittances than is average relatedness, even when we take account (by means of a multiple regression) of covarying influences on the level of remittance. But the effect is modest: less than a third of the observed level of remittances can be explained by our kin-altruism model.

Two points seem worth making here. (Actually, three, but I only have energy for two.)

1. Obviously, the precise results are going to depend on exactly how various aspects of the model are specified. (For instance, Bowles and Posel assume that money makes only a logarithmically-growing contribution to fitness.) However, they report that the results are at least reasonably robust to changes in the specification and assumptions, so there really doesn't seem to be any way to get inclusive fitness effects to account for all or even most of the remittances.

2. In calculating the inclusive fitness contributions of relatives of differing ages, they take into account the over-all growth rate of the South African population. In fact, however, "remittances are slightly better predicted using reproductive values assuming zero population growth (which was approximately the case in the ancestral populations of the migrants studied here)", and this "is consistent with the view that contemporary behaviour may be an adaptation to past conditions", rather than to present ones.

The Natural Science of the Human Species

Posted at March 23, 2005 17:47 | permanent link

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