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Hamilton’s Parasite Theory My take on Hamilton’s 1982 paper, which | consider his masterpiece, is a blend of his thoughts, Bob Trivers’ from a decade before, Richard Alexander’s, and maybe mine. Mine sees a population arranged in local “demes” which intrabreed in most cases for best adaptation to local pressures including pathogens and parasites. A local strain to which the local deme is adapted might spread to other demes which are not. Hosts in the invaded demes become sick. Female ones there intuit the degraded conditions, breed less often, and breed mostly females (mothers can choose) because males with their now ill-adapted anti-parasite (histocampatability) genes will find few willing mates. This begins the part from Trivers. I'll come to Alexander’s later. Mothers in the source deme see an opposite picture. Conditions are not necessarily better than before, but they are better than in the invaded demes. They intuit this, breed more often, and breed mostly males. The males migrate to those invaded demes, carrying histocompatibility genes pre-adapted to the invaders, and find willing mates there if they can show the signs. The idea that mothers choose to breed mostly males in prosperous conditions is the other half of Trivers’ idea. The idea that the invading parasite and the males with antidote genes might tend to originate from the same deme may be mine. That presupposes that females can trust the signs. Nature makes sure they can. She provides resistant males with hard-to-feign ones to prove it. This was one of Hamilton’s key insights. His idea has been called the “truth in advertising” theory. Symmetrical antlers, deep croaks, accurate songs and bright colors where they should be tell the females whose genes can be trusted. Parasites and pathogens would fake them in afflicted host males if they could. It seems they can’t. Hamilton, I believe, had solved three nagging puzzles at once. Why does nature waste resources on beauty displays that seem at first glance to hinder fitness? A Chapter 7 Petty’s Idea 2/3/16 8 HOUSE_OVERSIGHT_011067