Following yesterday’s post on female preference for masculine men, a couple of old articles came to mind.
The first (and I am not sure why this did not come into my head yesterday) is the work by Napoleon Chagnon on the Yanomamo. From his paper Life Histories, Blood Revenge, and Warfare in a Tribal Population:
Studies of the Yanomamo Indians of Amazonas during the past 23 years show that 44 percent of males estimated to be 25 or older have participated in the killing of someone, that approximately 30 percent of adult male deaths are due to violence, and that nearly 70 percent of all adults over an estimated 40 years of age have lost a close genetic relative due to violence. Demographic data indicate that men who have killed have more wives and offspring than men who have not killed.
The reproductive advantage to being unokais (having killed) was significant, with an average of 4.91 children compared to 1.59 for those in Chagnon’s sample who had not killed. To the extent that traits making someone more likely to kill are heritable, they would shortly dominate this population (assuming they do not already).
There is a gap between Chagnon’s study and the preference for masculinity that I wrote about yesterday. The unokais were reproductively successful with women who knew that they had killed. There is no evidence that the unokais appear more masculine and that this was behind their reproductive success. However, preference for masculinity in a violent society may be an indicator or proxy of what was Chagnon noted – that in violent societies there is benefit to being aggressive.
The second article was by Edward O Wilson, titled Competitive and aggressive behavior. After some very interesting discussion on the rate of behavioural change in humans, the closing paragraph was as follows:
Some degree of aggressiveness in man is nevertheless probably adaptive – that is, genetically programmed by means of natural selection to contribute to fitness in the narrow reproductive sense. This complex trait cannot be assumed to be due to a useless or harmful genetic residue left over from prehistoric times. It is more plausibly viewed as a trait that has been adaptive within the past few hundreds or, at most, thousands of years. Some of its components might have even originated during historical times, since both theoretical considerations and empirical studies on animal populations show that some behavioural traits can evolve significantly within ten generations or less.
If we accept this point, we might find genetically based variations in aggressiveness across modern populations. Extension of the research into female preferences for masculine males could shed some light on the strength of this adaptive advantage in modern populations and whether a cycle between violence and adaptive advantage for aggressiveness is a feasible scenario.