How Many Friends Does One Person Need?: Dunbar's Number and Other Evolutionary Quirks

In an entertaining and informative new work, evolutionary psychologist and Director of the Institute of Cognitive and Evolutionary Anthropology at Oxford, Dunbar (Evolutionary Psychology) investigates the ways in which evolution is still at work in homo sapiens, and the brain functions and abilities that separate us from other species. Covering an impressive breadth of topics and disciplines, Dunbar explores the ways in which our brains control every aspect of our social lives (surprise, we are less complicated than we think). Our needs, preferences, and commonalities are a function of what—not who—we are. Dunbar addresses the unusually large size of the human brain and concludes that monogamy is at fault; the brains of more promiscuous species are much smaller. Comparing the length of pregnancy in various species, he states that "human babies are born wildly premature"; in mammals, gestation time is dictated by the size of the brain, and humans "ought to have a gestation of twenty-one months." Full of interesting facts and Dunbar's winning personality, his effort reads like a fascinating lecture that most readers would be all-too-happy to attend. (Nov.)