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young. If all mothers invest preferentially in their own, or maximize Hamilton’s standard rb>c , healthier mothers will produce more young with higher doses of the antidote genes, while sicklier mothers will produce less with less. Here it is females who compete to prove the same better genes that males just proved in the tournaments or beauty contests. The race against parasites speeds up again with Trivers’ fine insight about healthier mothers choosing to dial up the ratio of sons to daughters (“primary sex ratio”), and to expand the reproductive period at both ends with shorter birth spacing for more male offspring still. (Some of this may be my idea rather than his.) Nature proves best current genes twice. Fathers prove them by duking it out or strutting their stuff. Mothers carrying the same best genes prove it by winning the breeding contest against other mothers after. The ex ante/ ex post distinction counts as much in biology as in economics. Here it accelerates the selection process. Offspring carrying the antidote gene to meet current parasites will generally not on that account cost more ex ante invested consumption to raise. If they are males, who can turn that advantage into many offspring, the ex post value of that same investment can be far higher. The converse works for offspring lacking the gene. Their mothers can make the best of it by producing females who will find breeding opportunities anyhow with mates carrying the gene, since she knows which they are and males always have cheap sperm to spare, and will so keep their own genes in the gene pool. Parasites got the last laugh by killing Hamilton on research in Africa a few years after I met him. I never knew well enough to call him Bill. Bob Trivers called him the deepest thinker in the world. That couldn’t be wrong by much. Parasites and Demes Ernst Mayr, Bob Trivers’ doctoral advisor at Harvard, defined a deme as a race or subpopulation that intrabreeds at least 95% of the time. I hypothesize that it does so, Chapter 7 Petty’s Idea 2/3/16 11 HOUSE_OVERSIGHT_011070