The Answer is "150"--And, for a Change, Not "42", March 7, 2010
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Robin Dunbar, Professor of Evolutionary Anthropology at Oxford University, offers a fascinating collection of essays about the evolution of humans and human society. The answer to the book's title, "How Many Friends Does One Person Need?", is somewhere around 150 (Dunbar's Number). From groups of hunter-gatherers to well-run corporations and armies, the number 150 is a basic (and maximum) building block for human organizations. Groups with fewer than 150 individuals can generally function on a first name basis--members can actually know, to one degree or another, everyone in the group. Groups larger than 150 tend to exceed the capacity of individual members to keep track of social complexity, which means that, like large corporate enterprises, they need heirarchy and management to preserve manageable group structures.
According to Dunbar, the complexity of human society--not tools, or walking upright, or hunting--it the primary force driving the growth of the human brain. Our brains enable us to speak and sing and otherwise communicate with each other without actually touching, so we can groom each other at a distance, so to speak. Because our social interactions don't require one-on-one contact, human groups can be larger than the groups of our primate cousins--but group size still has a limit, which appears to be about 150.
Dunbar's book is very readable and is filled with fascinating tidbits, like the fact that all human infants (even the ones who are carried to a full nine month term) are born premature. For our children to be born at the same level of development as, say, a chimpanzee, the gestation period would need to be about 22 months. Human children are born prematurely and require a great deal of parental care because that it the balance evolution has struck between large brain size, the woman's pelvis, and the woman's ability to walk upright. The relative helplessness of human infants puts an additional premium on pair bonding, communication and group support, thus driving a feedback loop rewarding bigger and more social brains.
Dunbar tackles a number of other intriguing questions about human behavior, including why are we often, but not always, monogomous? From which single conqueror are more than 8.5% of the men in Asia now descended? Why is gossip important? This book is an easy one to pick up and keep at, with each chapter drawing the reader in with yet another insight about the quirks that make us human. I highly recommend this book, along with Dubar's equally fascinating The Human Story