IN MAY 1846, a year and a half before gold was discovered at Sutter’s Mill, several extended families and quite a few unattached males headed with their caravans from Illinois to California. Due to poor organization, some bad advice, and a huge dose of bad luck, by November the group had foundered in the deep snows of the Sierra Nevada. They came to a halt at what is now known as Donner Pass, and, in an iconic if unpleasant moment in California’s history, they sat out winter in makeshift tents buried in snow, the group dwindling as survivors resorted to cannibalism to avert starvation.
From an evolutionary point of view, what makes the story interesting is not the cannibalism — which, in the annals of anthropology, is relatively banal — but who survived and who did not. Of the 87 pioneers, only 46 came over the pass alive in February and March of the next year. Their story, then, represents a case study of what might be termed catastrophic natural selection. It turns out that, contrary to lay Darwinist expectations, it was not the virile young but those who were embedded in families who had the best odds of survival. The unattached young men, presumably fuller of vigor and capable of withstanding more physical hardship than the others, fared worst, worse even than the older folk and the children.
For Robin Dunbar, an evolutionary biologist cum anthropologist, stories such as this one highlight how human kin networks aid survival — and, therefore, why people may take great pains to manufacture kin, via godparents for instance, or marriage, or by obscuring or playing up paternity. He points to another earlier case of extreme selection: of the Mayflower colonists who set foot on the American mainland in 1620, 53 of 103 died in the first New England winter. Here, too, mortality was disproportionately high among the unattached. To take a less dramatic example, several retrospective studies suggest that children embedded in large families get sick less often than those embedded in much smaller kin networks. Dunbar’s conclusion is not just the obvious one — that families share resources, and thus have advantages over less connected, well-endowed individuals — but also that being at the center of a web of interconnected relationships is therapeutic enough to increase one’s odds of withstanding pestilential (and presumably existential) slings and arrows.
Although we may think of family ties as raising stress hormones — after the holiday season especially — rather than immunity-enhancing endorphins, the fact is that in times of high mortality, kin relations matter hugely to survival. It follows, for bio-anthropologists like Dunbar, that we have evolved as a species to make them matter, and to feel bad if they malfunction. Even in a postindustrial society like our own, 76% of Americans say that family is what matters most to them, according to a recent Pew survey. If we did not have such gut-level assumptions about what families ought to be, if we did not at least hope that they might be weatherproof fortresses against the elements, then all the myriad threats to family and kinship would not be the stuff of gossip, and all the variants of real and imagined fratricide, of skeletons in the closet, and of familial betrayal, would not be the staples of our dramatic narratives.
Dunbar, who teaches at the University of Oxford and is Director of their Institute of Cognitive and Evolutionary Anthropology, has been important in fueling the recent wave of interest in evolutionary narratives. For the past thirty years he has conducted research designed to uncover the workings of our ancestral hardware: to decode the scripts that drive much of our behavior and make us what we are as a species. Although Dunbar emphasizes the value of kin, he is anything but a sentimentalist. In this book, he chases after averages and patterns, after predictive links between current behavioral and physical traits and what, in the Pleistocene or Neolithic past, would most likely have been mating or survival advantages. His 22 chapters, some of which are adapted from pieces written for New Scientist, are full of easily digestible sound bites, popularizations of his research and that of others working in the field. All of them perforce start from the premise that our behavior—especially the gut-level kind—is not rational or irrational per se, not good or bad, but is rather the result of adaptations that enabled our remote ancestors to out-compete the competition. We are the descendants of those who had a competitive edge. The intricacies of intra-species cooperation (which can itself be exquisitely competitive) — of managing family and other ties — are a large part of the game. Indeed, they may be the largest part of the game in fostering survival, in nurturing the young, and in allowing us to out-compete other primates. This is where not only kin networks but social networks enter the picture.
Our big brains — in particular our species’ inordinately large neocortex — evolved, Dunbar argues, in lockstep with our ability to manage increasingly large social groups: to read motives, to keep track of who is doing what with whom, of who is a reliable sharer, who a likely freeloader, and so on. Many evolutionary biologists have made this point over the years, of course. Where Dunbar is unique is in having assigned a definite number to what constitutes a stable human group or community. The “Dunbar’s number” of his title is (drum roll…) 150. Extrapolating from the estimated size of Neolithic villages, of Amish and other communities, of companies in most armies, and other such data, Dunbar argues that this number is, more or less, the limit of stable social networks because it represents the limit, more or less, of our cognitive capacities.
The number is highly debatable, but it turns out that, Facebook aside, the average person has about 150 friends — people he or she might actually recognize and be recognized by at a random airport, 150 people he or she might feel comfortable borrowing five dollars from. As for how many friends we have evolved to “need” in a more intimate sense, that is a different matter. According to Dunbar, most of us have, on average, about 3-5 intimate friends whom we speak to at least weekly, and about 10-15 more friends whose deaths would greatly distress us. These circles can include kin; indeed, the more extended family we keep in close touch with, the fewer friends we are likely to have — precisely because our neocortices can only manage so many relationships. What is perhaps most intriguing is the degree to which the inner circles change over time; close friends can drop through the circles of intimacy if we do not spend time with them, and even out of the 150, especially when someone new captures our attention. By contrast, kin have enough staying power that we can visit and expect to be housed by a cousin we have never met or a great-aunt after decades of neglect. In short, while friendships “decay” if not actively cultivated, kin relationships do not. Or so Dunbar claims.
Part of what makes reading Dunbar so entertaining is the sweeping nature of his claims. We do well to keep in mind that he is dealing with averages, which of course does not preclude the existence of plenty of outliers — in the case of social networks, for instance, individuals whom Malcolm Gladwell has called “connectors,” the people who seem to know everyone and whose 150 is presumably considerably larger than the average person’s. Other chapters in Dunbar’s book use the same rivetingly bold brush strokes to address a host of disparate topics—some of which have already made it into the popular media, a testament to how routine evolutionary explanations for behavior have become in our culture. Drawing on observational studies (of water cooler chitchat and such), he confirms an age-old stereotype: that “Harry likes to talk about Harry, but Sally talks about Susan.” Women’s conversations, Dunbar tidily explains, “are primarily geared to servicing their social networks, building and maintaining a complex web of relationships” in a socially untidy world, whereas men’s are more likely to be “a vocal form of the peacock’s tail” — in other words, a form of self-advertisement.
Yet another chapter discusses the dynamics of mate selection — and, again, Dunbar detects a robust pattern or signal by discounting the noise of confounding variables. His arguments mix the obvious with the less so: for instance, he shows that tall men have substantial advantages over short ones, and more symmetric women and men over less symmetric ones. “Symmetry,” or the degree to which the left and right halves of the face or the body mirror each other, seems to be the combined effect of what Dunbar calls “good” genes and of what might be termed “favorable” womb and early environmental conditions. Dunbar, unsurprisingly, emphasizes the genetic part. The point is that, in the mate market, we are rigged to fall for symmetry. Men tend to be drawn in addition to a certain “ideal” waist-to-hip ratio in women because, like youth and symmetry, it is a visible marker of health and fertility — or in other words, of the ability to produce robust progeny. In one of his inimitable turns of phrase, Dunbar jocularly advises his less well-endowed readers to “settle” in a pragmatic fashion for mates from the “bargain basement”:
Evolutionary theory suggests you should adjust your strategy to make the best of what may otherwise be a bad job. In other words, lower your expectations and settle for the bargain basement. It’s pure Jane Austen.
In other words, even though we may not be looking for a mate who can produce a gaggle of progeny, we still, at least initially, channel the ancestral script. Perhaps what’s most interesting here is how much human nature can be modulated by a postindustrial environment, with its rapidly changing gender norms and procreative aims. Dunbar does not say much on the subject — though, he notes that, according to one study on “Lonely Hearts”/Singles adverts, women in general are increasingly “seeking” men with companionate skills (sharing/caring traits) over the traditional pick (an older man with economic resources à la Jane Austen’s Darcy). Aging men, however, are, slower to tweak the ancestral script; at least according to the ads they place, they still fixate on women in their late 20s. This happens to be the tail end of women’s peak fertility — and so, according to Dunbar, this fixation makes Darwinian if not economic or indeed any other kind of sense. Only by age fifty or so have most updated enough to radically “downgrade their demands.”
Several chapters highlight how much emotions or gut responses precede or color reason in other arenas. Emotions can of course dramatically and irrevocably upend otherwise-weather-tight kin networks, not to mention social ones in general. We need only think of more humdrum variants of Othello’s volcanic jealousy. It turns out that brain scans reveal that most decisions in fact have their origins in the amygdalae (the part of the limbic system that processes emotion), only afterward migrating to the neocortex, which does a disturbingly seamless job of rationalizing gut responses. Dunbar is happy to cite a famous, fairly recent brain scan study that suggests conservatives have more reactive amygdalae than liberals: they experience threats more viscerally, and so, as a result, may be more susceptible to the antics of fear-mongering demagogues. The point Dunbar wants to make here is that politics is largely, perhaps mostly, about physiologically-mediated emotional responses. Again, height and facial symmetry play an outsize role, according to him. Regarding the last Presidential election, Dunbar baldly asserts that Barack Obama’s victory against John McCain was “a foregone conclusion” — because Obama was taller and his face more symmetric! As in the mate market so in our leaders, we apparently cannot stop ourselves from “falling” for these traits. Yes, it is hard not to find the Dunbar formula disturbingly simplistic (and empirically inadequate, Mitt Romney being both taller and more symmetrical than McCain). Then again, one suspects an ugly Sarah Palin would have little traction. And perhaps a homely Obama would not have had much either. And an asymmetric Helen of Troy would of course not have launched a thousand ships.
Dunbar’s patterns, formulas and numbers are certainly fodder for speculation, and indeed grist for thought in general. And they are vastly entertaining. This said, he does not always rise to the level of the best popular science writing — precisely because his brush is so thick. Sometimes this reader wished for a thinner one capable of painterly chiaroscuro, or call it nuance. He also writes rather loosely about the evolutionary process, about genes, about the architecture of the brain; and he has little to say about some important developments, like epigenetics, which emphasizes the ongoing feedback loop between genes and environment. Nor does he highlight the ways in which variability — the presence of non-average traits or behaviors — may confer group-level or indeed species-wide survivability. He can fall prey, too, to a certain stylistic dissonance. For instance, we are told at the outset of his book that he “invite[s]” us “to explore those parts of [ourselves]” that “even the most proverbially exotic beers can never reach.” This sounds like a mix of self-help language and slightly off bonhomie. Finally, a rather cloying vanity obtrudes at times: in one chapter, he paints scientists (himself included) as “Renaissance” men and women who play musical instruments and know their poetry, as compared to those who hold degrees in the humanities, whom he paints as too narrowly provincial and myopic to see the importance of science. Here, one might conclude that Dunbar is himself not immune to some of the evolutionarily refined biases he dissects; these presumably compel him to “self-advertise” and scapegoat willy-nilly the tribe, or what he may consider the “out group” across the campus green.
Of course, this does not change the wider significance of his work. Indeed, in general, understanding the Darwinian back-story of our species is arguably a way to short-circuit the infelicities of our gut responses: a way to combat gut-level racism, sexism, beauty/symmetry biases, height biases, ageism, and the many variants of tribalism and jingoism. Perhaps it is unfair to expect Dunbar himself to transcend the evolutionary legacy. It is enough that he tries to name and codify our biases: that he peddles self-understanding and so, presumably, humility over vanity. Indeed, in another chapter, Dunbar shows that, if we go far enough back in our family trees, we are all the product of a tangled skein of heroes and villains, of conquering populations and conquered ones, of dominant and minority races, of in-groups and out-groups. Whether we as individuals call ourselves one or the other is often just a matter of how far back in time we set our stakes combined with the limits of our instruments for probing ourselves. Knowledge such as this may well be the only way out of the ancestral cave.