Over the weekend I picked up William McNeill’s “Plagues and Peoples”. I’ve already read an updated version of some of the same ideas in GS&S, but Razib has mentioned some facts in the 70s classic which were new to me, and I hoped there would be more. Plus, it’s unconscionable for Matthew Yglesias to know any science I don’t (Copernican Revolution, your day will come!)

In addition to diseases transmitted by flies, fleas and lice, McNeil mentions schistosomiasis as being transmitted by snails. I had never heard of that disease before, or known that there are any snail-borne human diseases. But checking that out on wikipedia, it seems the snails are more analogous to rats in that they carry a multicellular parasite.

Later on he says that herds of ungulates survived in Africa because the sleeping sickness carried by tsetse flies (which follow the herds) drove humans away. That seems strange to me because there are cattle-herders in Africa, and that may not have occurred until relatively recently (less than 10,000 years), I still don’t think the early herders had any defenses against the flies or disease. Cattle themselves may be an import from elsewhere, but I don’t think they repel flies any more than the more indigenous herds.

McNeill depicts humanity as arising in a hot, humid region with ferocious microparasite competition and then moving onto colder, drier regions where game animals were easier prey (not having evolved alongside anatomically modern humans and developed defenses). Then he makes the point that before the age of microscopes and antibiotics, human intelligence had little ability to deal with invisible microparasites. Jared Diamond used that logic to suggest that his New Guinean friends should be more intelligent than the dominant Eurasian civilized people who faced more disease than homicide. McNeill suggests something like Rushton’s theory in which colder climates put more selection pressure on intelligence rather than disease resistance.

He also says that since warm, wet climates are more natural for humans, those who crossed over the Bering Strait were kept at an equilibrium with their game but on moving south to easier climes large game was wiped out. I was going to point out the llama’s of South America as an exception, but they live up in cold dry mountain regions.