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

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Why are we the way we are?

That simple question has bedevilled humanity since the dawn of recorded history, provoking various answers from philosophers, mystics, theologians, fabulists, humorists, cynics, politicians, and, only in the last 300 years or so, from naturalists and scientists.  The latest discipline that seeks to unriddle the mysteries of human behavior and mentality, abilities and customs, is that of evolutionary biology, or evolutionary anthropology.  Taking a thoroughly up-to-date Darwinism as their core set of tenets, these practitioners seek to tease out the formative influences from our hominid past—and beyond—that endowed us with ingrained behaviors and modes of thought that often translate directly into the institutions and cultural practices of our everyday lives.

Robin Dunbar is one such fellow, so successful at the task that he's had what seems to be an invariant natural fact named after him.  "Dunbar's Law" holds as its most basic formulation that the average human can sustain no more than 150 relatively close friends and relatives in any kind of practical and useful network.  (The law scales up and down for different kinds of groups.)  Over the past fifteen years Dunbar's been explicating similar nooks and crannies of evolutionary biology in such periodicals as New Scientist and the Scotsman.  Now he gathers up these pieces into one fascinating volume that ranges widely across time, space and human practices.  As Dunbar says at one point, "Evolution has saddles us with a whole series of cheap chemical tricks that play a far more important part in our behaviour than most of us would like to think."

Tossing off light-hearted examinations of such fairly innocent topics as why we kiss and why all babies look very much alike, Dunbar is unafraid to tackle sensitive and controversial issues as well.  These essays deal with race, gender, intelligence, class, and nationality in dispassionate and unflinching  ways that do not seek to cushion hard facts with mealy-mouthed sanctimony.  In "Farewell, Cousins," a look at extinction events, Dunbar forthrightly addresses the overbreeding of our own species, and admonishes, "We really do need to get the world's population growth seriously into reverse."  When's the last time you heard any politician or preacher say such a thing—at least from a scientific, non-ethnic-cleansing standpoint?

Dunbar is cheerfully mordant about our tendency to apply the wrong yardstick and tool to just about any given situation, thus triggering a host of unintended consequences.  The chapter titled "Stone Age Psychology" opines that "We can expect much of our behaviour to be deeply out of kilter with the circumstances we find ourselves in now.  In fact, maladapted, not to put too fine a gloss on it."  But he also finds much hope and promise in the plastic nature of our minds, placing great stock in our capacity for "intentionality," the ability to run virtual simulations of the minds of others, an ability we share with no other species.  (He identifies six levels of intentionality in Shakespeare's work, one level more than most of us employ.)  Far from being a catalogue of gloom and doom, this book leaves the reader marvelling at how far homo sapiens has come, and how far we might yet ascend.

As lagniappe for American readers, Dunbar's essential endearing Britishness is oft on display.  "So how much time did you waste yesterday wittering away nineteen to the dozen?"  It's a test of intentionality to parse that one!

-PAUL DI FILIPPO

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Paul Di Filippo's column The Speculator appears monthly in the Barnes & Noble Review.  He is the author of several acclaimed novels and story collections, including Fractal Paisleys, Little Doors, Neutrino Drag, and Fuzzy Dice.