On the site for their new book, The 10,000 Year Explosion, Cochran and Harpending share some “deleted scenes” that didn’t make it into the book, including this piece, which examines some simple population models and demonstrates an interesting result when you add a lethal disease — malaria, in this example — into the mix:
There is more than half again as many resources per person now than there was before malaria appeared. What this means on the ground is that people do not have to work very hard to get enough to eat, that there is fruit on the trees for plucking, and that there are not great labor demands on anyone.Gregory Clark (Clark 2007) points out that the medieval Englishman had a higher standard than a medieval Japanese because there was much more sewage and filth in England and so a heavier burden of disease. This extra disease translated, as in our malaria example, to a lower population density and higher standard of living.
What are the social consequences of this new disease for our population? The most important immediate consequence is that there are plentiful resources for everyone and so, following the nature of the creature, males withdraw from subsistence work as they find that they can simply parasitize women for food. In much of central Africa the result is societies in which men don’t do anything very useful and women provision themselves, their children, and the men. The euphemism in economics for this kind of society is “female farming system.” Left free of the demands of subsistence we expect the men will start hanging out together, perhaps even all moving into a village men’s house (not so common in Africa). This may soon lead to local and regional raiding and warfare and an entrenched culture of local violence.
The warfare itself may cause enough excess death that a female farming system is sustainable even in the absence of a killer disease. Highland New Guinea, for example, seems to have had a classical cad system for millennia or more. (Ethnographic shorthand for societies where males put a lot of effort into competition with other males is that they are cad societies as opposed to dad societies where male effort is directed to provisioning a male’s own family.) Of course there are other contributing factors here like the extremely broken terrain that makes the establishment of a larger polity with an effective constabulary difficult or impossible.