content notes: rape, infanticide, murder

Hunter-gatherers’ primary method of population control is infanticide, and they preferentially kill female children. Some of the reasons are that men are more useful for defending the family and tribe (women basically never fought, although this changed a little bit after archery, except in home defense), and for obtaining food, especially in areas (like the Arctic) where foraging yields much less than hunting.

So, how strong is the sex imbalance?

Infanticide is often covert and attributed to accidents, but census statistics of pre-industrial societies tell an unmistakable story. Although the number of male and female babies should be nearly equal at birth (105:100 in favour of boys), there are many more boys than girls in childhood. Surveys of hundreds of different communities from over 100 different cultures (of which about a fifth were hunter–gatherers) has shown that juvenile sex ratios averaged 127:100 in favour of boys, with an even higher rate in some societies. The Eskimos are one of the most extreme cases. Their harsh environment made them wholly dependent on male hunting, whereas female foraging played a greater economic role in milder climates. Thus female infanticide was particularly widespread among them. They registered childhood sex ratios of 150:100 and even 200:100 in favour of boys.

So, this is awkward, because fighting over women is one of the primary causes of hunter-gatherer conflict and warfare. The standard objective of a raid – the primary form of lethal conflict across hunter-gatherer societies – is to kill all the enemy men, grab their stuff, and kidnap the women. There’s a quote from an Australian hunter-gatherer man asked by an anthropologist whether his motivation for a raid was food, and responds, ‘Even though we like meat, we like women a whole lot more!’ In unfortunate addition, the more insecure a society is about warfare the more it’ll prefer to have male children:

In this way, as statistical studies show, male and female numbers in primitive societies—highly tilted in favour of males in childhood—tend to level out in adulthood. Violent conflict is thus one of the principal means through which competition over women is both expressed and resolved. Furthermore, as Divale and Harris have shown, there is a vicious circle here: in societies that lived under the constant threat and eventuality of violence, families’ preference for males who would protect them increased.

Note that it’s not just that you can resolve competition by kidnapping your enemy tribe’s women – in the process of going to war, some men on your own side will die, decreasing the competition pressure.

Cool, cool. So, competition for females is a primary driver of hunter-gatherer warfare. Time to have… polygyny!

Polygyny was very common in hunter-gatherer societies – although approximately the majority had one wife, the most powerful men almost always had multiple, and the wife Gini index goes up the more resource-dense an environment is. “There was a direct correlation of resource density, resource accumulation and monopolization, social ranking, and polygyny.” – the more resources you can accumulate, the more mouths you can feed in your family, the more clout you can have in your community to take more wives without resentment blowing up. In the resource-scarce Kalahari Desert, !Kung men are largely one-wife, but 5% of married men had two wives. The case is similar among native Eskimos in the mid-Canadian Arctic. In contrast, studies of Australian tribes say that 10~15% of married men have three wives. In even more productive Australian land, a few men hit double digits of wives. As you may guess:

Polygyny greatly exacerbated women’s scarcity and direct and indirect male competition and conflict over them. Indeed, a cross-cultural study has found polygyny to be one of the most distinctive correlates that there is of feuding and internal warfare.

Incidentally, this makes the question of when and how monogamy became so entrenched as the default in Western society fascinating to me, because it seems incredibly useful – I assume it mitigates a primary source of violent conflict, and helps large-scale societies hold together. I wonder whether it’s linked to the success of Christian societies.

The fact that the male/female sex ratio is so (artificially) imbalanced to start with but levels out as men die off seems to have affected the timing of male puberty.

As mentioned earlier, among the victims of male competition for women are the young adult males, who are obliged to postpone marriage for quite a long time. This universal and probably very old trend among primitive human communities has some interesting evolutionary consequences. Men reach sexual maturity at an older age than women, which is quite the opposite from what we would expect in view of the fact that man’s reproductive role and reproductive organs involve a much lighter physical burden than the woman’s. The main reason for this later male maturation seems to be male competition. Men are given a few more years to grow up and gain strength before being exposed to potential violent conflict.