Friday, August 26, 2005

Conditional response....   posted by Razib @ 8/26/2005 12:46:00 AM


Evolutionary biologists mostly assume that polygyny increases sexual dimorphism in size because, under polygyny, larger males monopolize mating opportunities and pass on their ‘large male’ genes to their sons. Available data on parent–child correlations in height among humans (Homo sapiens) do not support the crucial assumption that height is transmitted along sex lines. This paper instead suggests that human sexual dimorphism in size emerged, not because men got taller, but because women got shorter by undergoing early menarche in response to polygyny. It further speculates that, rather than genetically transmitted, the sexual dimorphism may emerge anew in each generation in response to the degree of polygyny in society. The analysis of comparative data supports the prediction that polygyny reduces women’s height, but has no effect on men’s, and is consistent with the speculation that the origin of human sexual dimorphism in size may be cultural, not genetic.
The authors present evidence that women who enter menarche earlier reach a shorter adult height while in societies where polygyny (defined as male reproductive variance:female reproductive variance) is more pronounced also tend to exhibit more sexual dimorphism. At the end of the paper the authors hypothesize that a biological-proximate process that might affect menarche are pheromones produced by the father which interact with his daughter's physiology. Evidence which shows later menarche for girls who spent a greater time with their fathers is brought forward, the logic being that polygynous fathers can provide their daughters far less individual attention (ergo, pheromones).

Related: Father absence and reproductive strategy: an evolutionary perspective.