HUMAN EVOLUTION

A history of the “insatiable curiosity about who we are and where we have come from.”

Histories of human evolution rely on stones and bones because that’s all that remains of our ancestors. That works well for anatomy but not so well for culture or consciousness. British evolutionary psychologist Dunbar (How Many Friends Does One Person Need?: Dunbar's Number and Other Evolutionary Quirks, 2010, etc.), former director of the Institute of Cognitive and Evolutionary Anthropology at Oxford, attacks the big questions: “What is it to be human (as opposed to being an ape)? And how did we come to be that way?” He offers a series of lucid but definitely not dumbed-down answers. During the 1990s, scientists developed two approaches that did not require artifacts. The first is the social brain hypothesis, which argues that intelligence evolved not to solve ecological problems but to thrive in social groups. Studies show that primate brain size is proportional to the complexity of the species’ social interactions. Dunbar concludes that humans best maintain stable social relations with 150 others, a figure known as Dunbar’s number (modestly not named by the author). The second is the time budget model. Primates fill a 24-hour day with travel, feeding, socialization, and rest. Changing one affects the others. Thus, the huge Homo sapiens brain requires a great increase in energy intake. How did we accomplish this without squeezing other activities? Some answers: eating meat, inventing cooking, saving energy by shrinking our gut, and traveling faster with our longer legs. Dunbar delivers impressive accounts of brain scans, genetics, sociological research, and animal and human psychological studies but no tales of intrepid anthropologists suffering in the desert.

Readers who pay attention and do not skim the many graphs, tables, and statistics will discover a rich trove of discoveries on how primitive primates became modern humans.