Anthropologist Peter Frost blogs:
This has long been the case with simple ‘horticultural’ societies in the tropical zone. The women feed themselves and their children with minimal male assistance because they can grow food year-round. And this food production is not appropriated by a State or a land-owning class.
Such societies remain simple in large part because intense sexual competition keeps them from evolving into more complex entities. The surplus males stir up endless conflict, if only because their sole access to women is through warfare, i.e., rape and abduction. There can never be pacification and, therefore, the formation of larger, more advanced societies.
A high incidence of polygyny favors men with a different toolkit of physical and mental traits. Some personality traits, for instance, will be more advantageous than others. Such is the finding of a series of studies from rural Senegal, where 48% of men over 40 are polygynous.
Alvergne et al. (2009, 2010a, 2010b) found no correlation among Senegalese men between mating success and most personality traits, i.e., neuroticism, openness, and agreeableness. One trait, however, showed a strong correlation. This was extraversion, defined as “pro-social behavior which reflects sociability, assertiveness, activity, dominance and positive emotions.” Men with above-medium extraversion were 40% more likely to have more than one wife than those with below-medium extraversion, after controlling for age. Furthermore, this personality trait correlated with higher testosterone levels. Such a linkage suggests that extraversion is part of the male toolkit for mating success in a high-polygyny environment.
Perhaps this goes along with the notion of a mid-latitude Jealousy Belt (Sicily, Lebanon, Afghanistan, etc.), where life is full of interest because men tend to be extraverted and on the prowl but women remain major investments.