THE 10,000 YEAR EXPLOSION

Physicist Cochran and anthropologist Harpending team up to recount changes in population genetics that they say mark an explosion in human evolution.

But do they? The post–Ice Age rise of civilization, particularly the invention of agriculture and domestication of animals, led to a population explosion, changes in diet, new diseases and challenging environments as people spread across the globe. But we are still one species, still stuck with evolutionary compromises like back problems and painful childbirth to accommodate walking upright. The authors mostly report on adaptations during the past 10,000 years of local groups, such as barrel-chested Bolivians living at high altitudes or sickle-cell trait carriers protected against malaria. Give Cochran and Harpending (Anthropology/Univ. of Utah) credit for explaining that these are the result of rare beneficial mutations that propagate in groups because of the survival advantages they confer, and also for explaining how world genetic maps are enabling the tracing of adaptations. The authors provide sundry examples, noting that as populations increased, so would the number of mutations, which could spread via trade routes, conquest, colonization and intermarriage, activities that reflect cultural evolution. They breeze through the millennia, glibly opining that modern Homo sapiens interbred with Neanderthals or attributing the Spanish success in the New World to the Amerindians’ lack of immunity to disease (no mention of the conquerors’ use of horses, for example). Their speculation reaches its apogee in a declaration that Ashkenazi Jews have developed high intelligence because they were largely an inbred group restricted to cognitively demanding jobs as financiers or merchants, and that recessive neurological diseases common to Ashkenazis, such as Tay-Sachs, are associated with expanding neural connections in the brain. Readers’ exasperation will only grow as these conjectures are interspersed with such statements as, “It has been shown that poets are unusually likely to be manic-depressive.”

An overreaching travesty that could have been a useful compilation of genetic modifications over time.