Agriculture in Malthusian conditions must have also favored individuals who were metabolically efficient and could produce the maximum work for a given amount of food. Among hunter-gatherers the selective pressures were different—in their way of life, bursts of strength in war or hunting were relatively more important. We see differences in the gene alpha-actinin-3 (ACTN3) that may reflect this. The gene has two forms—one
that produces a protein that is active in fast-twitch muscles, and one that produces no protein at all. The intact version of the gene increases muscle power and is noticeably more common among world-class sprinters than in the rest of the population; the other version of the gene increases aerobic efficiency and endurance. Gene-engineered mice with the endurance version of ACTN3 can run 33 percent farther than standard lab mice before exhaustion sets in.24 Both forms of ACTN3 are found in all populations, but the endurance form appears to have become more common since the advent of agriculture in Europe. We suspect that it made peasant farmers more productive. （p.117, Ch.4, The 10,000 Year Explosion）