Among all your friends and acquaintances in real life, how many exactly are those with whom you carry close social relationships: those whom you know well enough that you can ask of them a favor, or whose discussion you can join uninvited without fear of getting shunned as epal or obtruder? Our individual answers will no doubt vary, but the eminent anthropologist Robin Dunbar would bet on an average that now carries his name – 150. Dunbar’s number.
There is nothing to read into the number by way of superstition, although it does tell us much about our fortune in evolutionary terms. That figure turned up when Dunbar, using a statistical equation, tried to find out what size of social group correlates with another figure on hand – that for the relative brain size of humans. He takes “brain size” as the ratio of the size of the neocortex – the newest, reasoning part of the brain – to the size of the rest of the brain. The ratio for humans is 4:1 – meaning, the neocortex amounts to 80% of the whole human brain. It happens to be the highest among all mammalian species, and its matching social group size too is the biggest.
But there’s more to Dunbar’s number than its number alone. For Dunbar, it serves to measure the complexity of handling and sustaining genuine social relationships: knowing who your friends are and how they relate among themselves, while keeping all these and related knowledge in mind to guide your relationships with each one of them – balancing conflicting interests, pleasing them, making them happy.
As group size grows, social complexity increases dramatically. If you’re in a group of 10 people, you would need to keep track of 45 two-way relationships. If group size doubles to 20, however, two-way relationships jump four times to 190. The capacity to process the information churned out by these relationships has to grow accordingly. From human evolution’s point of view, the adaptive pressure for the neocortex to grow bigger seems to stem from the need to “weld” bigger groups together. Meet the social brain hypothesis.
The key idea underlying the correlation is less about the number of relationships in a group than about their quality. What then lends quality to group size? How do you come to know it if it’s there? Dunbar turns first to other species of primates – chimps, apes, monkeys – for insights and looks into one of their observable traits, grooming. Primates groom their friends, and do so enthusiastically, but not mere acquaintances. Grooming partners help each other mutually and demonstrate stronger bonds among themselves than with non-grooming ones. Grooming is bonding, a way of connecting.
Existing studies on primates yielded data on grooming frequencies in 24 species, which allowed Dunbar to derive the mean size of grooming cliques (sets of individuals with high grooming frequencies). The grooming clique size matched up well with neocortex size and total group size. This suggests that as group size grows bigger, the animals find themselves forming bigger grooming cliques too, for which a bigger capacity for processing information is needed, leading to a strongly bonded coalition. Partners get to enjoy protection in return and an improved chance of survival, on top of the apparent hygienic and feel-good benefits derived from grooming.
As a one-on-one activity, however, there’s a limit to the number of partners one can groom given a time budget for a day, which cannot be stretched without cutting the time needed for getting food and eating. Researches show, for example, that chimps spend no more than 20 percent of their day for social grooming, given a social group size of 55 at the most. Against the backdrop of a relentlessly growing size of social group, which puts a pressure for expanding one’s circle of allies, grooming time would increase perilously close to eating up the time allotment for earning a living. Evolution presents primates with a problem: how do you keep on servicing your expanding relationships while giving yourself enough time for foraging and eating? An ingenious adaptive mechanism is one that lets you groom, say, three friends at the same time; ergo, your group size could grow to 150 with no risk of starving your species into extinction.
That mechanism, Dunbar speculates, is “vocal grooming,” which saw the need for language and brain to coevolve, and along with them, speech. Strongly hinting at this mechanism are the richly varied alarm and contact calls – hoots, screams, moans, grunts, whinnies – that apes and monkeys raise when in danger or to warn others of it.
Language overcomes the constraints of physical grooming by letting you “groom” – chat, talk with – several others at the same time. (FYI: The word chat comes from the chattering sound that monkeys make as they dispose of parasites with their teeth while grooming each other.) It also lets you “groom” from a distance and serves to substitute for physical grooming in replicating the feel-good (opiate release ) effect it gives to the groomed, and in building trust and knowing your allies indirectly through others, like knowing Juan through Maria. In place of vocal grooming, Dunbar prefers the more familiar word, gossip. Dismissing the existing theories on the origin of language, he offers his own: “Language evolved to allow us to gossip.”
Language is the social tie that binds. It facilitates the exchange of information on group members; it lets you keep track of them. But not all is rosy. At the very base of group relationships is the Golden Rule or reciprocity: you groom me, I’ll groom you back. A heavy investment of trust is needed for the trade to happen, and risk goes with it. Untrustworthy are the cheats who refuse to groom you back when their turn comes; they won’t be there to return a favor when you’re in trouble. In physical grooming, the actual investment of time would tend to hold one back from cheating. Besides, you can’t fake picking nits or combing the fur of another. Cheating is directly observable.
With language, however, you can lie. You can build yourself up with fake stories; you can manage your reputation (self-advertisement) if you can work on others’ perception. Vocal grooming makes it more difficult to keep tabs on cheaters as social groups grow larger and larger. But language holds the counterpoise of sharing information about cheats through the grapevine. Experimental evidence points to the power of gossip as a mechanism for deterring cheats. Mathematical models show that “free riders would be less successful in a community of gossiping co-operators.”
Language facilitates group bonding by replacing contact grooming with gossiping. How does this hypothesis fare against the reality of social groups today? Studies show that indeed the size of casual conversation groups is limited to four persons: one talks and three listens, or 1 grooms 3. And what are they talking about? Over two-thirds of the time they are into social topics – personal relationships, likes and dislikes, experiences, other people. No other single topic – politics, sports, religion, etc. – takes 10% of the time.
Talk marks us out as humans. But it’s not the talk of the wise that makes the world go round; it’s the small talk, the chattering, the tittle-tattle of life that do it. “We are social beings,” writes Dunbar, “and our world - no less than that of the monkeys and apes - is cocooned in the interests and minutiae of everyday social life. They fascinate s beyond measure.”