How many friends do you have?

Robin Dunbar knows

In the 1990s British anthropologist Robin Dunbar asserted a connection between brain size and the number of social relationships primates can maintain. His data led him to conclude that humans can get to know about 150 other humans in a meaningful way. This number, soon called Dunbar’s number, was found to be characteristic of the size of bands or similar groups in numerous pre-modern cultures.

Dunbar hypothesized a causal connection. Beyond this number, individuals of the group couldn’t know each other well enough to interact on a personal basis. Other researchers drew inferences, including that when a population exceeded the Dunbar number, institutions of government, religion or other coercion were necessary to keep the society from flying apart.

Dunbar’s claims have been challenged. He himself has acknowledged that the number could be as low as 50 or as high as 250, depending on circumstances. And he points out that he didn’t call it the Dunbar number; others did.

But most people who have thought about the matter think there is something to it. Very few people in any society can get to know several hundred others well enough, as Dunbar put it, to comfortably join them uninvited for a drink in a bar. The rest of us have more modest circles of friends.

To the extent that the principle holds across time, it can explain important aspects of history, not least the history of the United States. A problem that vexed relations between the American government and tribes of Indians during the eighteenth and nineteenth centuries was the incommensurability of the size and power of the parties to treaty negotiations. On one side of a typical parley was the government of the United States, representing its millions of citizens. On the other was a chief or group of chiefs, typically representing the few hundred members of their bands.

The Indian nations, or tribes, were larger than that. The Comanches numbered perhaps fifteen thousand, the Lakotas half again that many. But neither tribe had anything like a government that could credibly speak for the nation as a whole. Still less did it have mechanisms for compelling obedience by all Comanches or Lakotas.

The negotiators for the U.S. government were aware of this. Sometimes they ignored it and hoped for the best. Sometimes they cynically exploited it, negotiating treaties with chiefs who could be persuaded or bribed and then acting as if those treaties bound all members of the tribes.

Indians gamed the system, too. Most of the treaties promised annual payments from the U.S. government to the tribes. Some members of the tribes would make sure to be on the reservations when the annuities were delivered, to receive their share; then they would take off for the old hunting range, disavowing any obligation to observe the treaty stipulations.

A few of the tribes had structures of leadership that more closely resembled those of the whites. Indeed, Benjamin Franklin cited the Iroquois confederacy as an example of what Britain’s American colonies ought to fashion to align their interests amid their struggles against France.

Yet many of the tribes still operated according to the Dunbar model. By most accounts, their systems of personal government, based on consensus rather than coercion, served the domestic purposes of their bands well. And they sufficed, in many cases, to deal with rival bands and tribes with comparable modes of organization.

But against a system that had transcended the Dunbar limit, they stood little chance. Governments like that of the United States institutionalized coercion; as a matter of course American officials compelled people they had never met to pay taxes, to serve in the military, to obey laws established by distant bodies of men. Such governments can mobilize resources far beyond the reach of any band or Dunbar group.

Indeed, for purposes of mobilization, the breaking of the Dunbar limit is probably essential. Coercing friends and close acquaintances is fraught with spillover effects. You might outrank your brother-in-law, but he’s not going to take orders from you without a quarrel. And if you win that argument, you’ll have to deal with the unhappiness of the kin you two share. Bureaucracies are faceless for a reason.

For what it’s worth, the Dunbar limit applies to enemies as well as friends. It’s a question of processing power and storage in the human neocortex. If you multiply your enemies, you reduce your capacity to have friends. This might be why when groups or cultures identify enemies, they often focus their attention on one or a few special villains: King George (instead of Parliament), Napoleon (in lieu of the French nation), Hitler and Hirohito (rather than all Germans and Japanese). Think of it as a kind of conservation of energy.

It’s a good idea for individuals, too. Make fewer enemies and have more friends.