Thursday, March 26, 2009

Finnish Type A personalities have more offspring   posted by Razib @ 3/26/2009 03:45:00 PM

Adolescent Leadership and Adulthood Fertility: Revisiting the "Central Theoretical Problem of Human Sociobiology":
Human motivation for social status may reflect an evolved psychological adaptation that increased individual reproductive success in the evolutionary past. However, the association between status striving and reproduction in contemporary humans is unclear. It may be hypothesized that personality traits related to status achievement increase fertility even if modern indicators of socioeconomic status do not. We examined whether four subcomponents of type-A personality-leadership, hard-driving, eagerness, and aggressiveness—assessed at the age of 12 to 21 years predicted the likelihood of having children by the age of 39 in a population-based sample of Finnish women and men (N=1,313). Survival analyses indicated that high adolescent leadership increased adulthood fertility in men and women, independently of education level and urbanicity of residence. The findings suggest that personality determinants of status achievement may predict increased reproductive success in contemporary humans.

In Finland a "Type-A Personality" presumably refers to someone willing to make eye contact with family members. In any case I think this table is probably the most informative:

The main caveat which is stated in the paper is that we're talking about Finland today. How generalizable is this? If leadership was a primary factor behind reproductive success over long periods of time how come we're not all Type A personalities? I think it seems likely that the fitness of these individuals and their morph exhibits frequency dependence. Additionally the longer term volatility of this strategy probably differs from more retiring personal profiles. The Type A strategy seems more likely to be subject to winner-take-all dynamics; there were many prominent leaders on the Mongolian plain of 1250. Very few of them have descendants due to the fact that one Type A eliminated all the rest. In Farewell to Alms Greg Clark reports data which illustrate that before the 19th century the blooded military nobility might have had below average replacement because of morality during war. In contrast, the gentry were fertile. Not to nerd out, but this shows that the Hobbit strategy can beat the Numenorean over the long term. Modern post-industrial societies have a particular social ecology, and are subject to a dynamic contingent upon that ecology. Let's not overgeneralize.

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