The evolution of human diversity : a phylogenetic approach
The socio-ecological correlates of cross-cultural variation in lactase persistence, sexual dimorphism in stature, and wealth inheritance in Africa were investigated, using phylogenetic comparative methods to control for the non-independence of populations (Galton's problem). Felsenstein's method of comparative analysis using independent contrasts, and Pagel's phylogenetic maximum likelihood model, were used. Genetic and linguistic trees were used as models of the past relationships among populations. Lactase persistence was found to be associated with pastoralism but not with solar intensity or aridity. This is consistent with the hypothesis that high lactose digestion capacity in adults is an adaptation to dairying. This result does not support the hypotheses that low solar radiation at high latitudes and aridity are additional selective pressures for lactase persistence. Cross-cultural variation in stature was associated with women's work. Women are taller, relative to men, in societies where women contribute more to subsistence. In Africa, patrilineal wealth inheritance is associated with pastoralism and polygyny. Patrilineal wealth inheritance is adaptive if inherited wealth benefits sons more than daughters, which is probably the case in both polygynous and pastoralist societies. It is hypothesised that matrilineal inheritance arises from wealth inheritance to daughters. Inheritance to daughters is adaptive if the additional benefits of wealth inheritance to sons do not outweigh the risk of paternity uncertainty of sons' offspring. The transmission, between populations, of those bio-cultural traits in the comparative analyses was also investigated. The association between each trait in a population, and that trait in the population's phylogenetic sister-group and nearest geographical neighbour(s) were compared using regression. The majority of traits were found to be associated with phylogeny. Some traits showed an additional association with geographical neighbours. Vertical transmission, from `mother' to `daughter' populations, appears to be more important than geographical diffusion between neighbouring populations, for the majority of the traits tested here.