The size of your brain can predict how many friends you have

We recently learned a bigger brain doesn't necessarily mean a better brain, but here's a potentially major exception. Your ability to make and maintain friendships appears to be linked to the size of one particular region of the brain.

It's sometimes said that you can know a person by looking in their eyes, but in this case you'll need to look at the part of the brain right above the eyes. That's where the orbital prefrontal cortex is found, and it's that particular region that, according to a team of British researchers led by Oxford's Professor Robin Dunbar, plays a crucial role in our ability to sustain lots of friendships long-term.

The main idea here is that the key to being friends with others - and we mean actually friends here, not just acquaintances - is being able to understand another person's perspective and understand what they're thinking. This knack, which the researchers give the rather nifty names of "mind-reading" and "mentalizing", is vital to tasks as basic as just holding a conversation, and it's essential for keeping relationships going. Generally, this sort of thing happens on an unconscious level, and Professor Dunbar points out how fiendishly complex this mind-reading can become when utilized by a master:

"'Mentalizing' is where one individual is able to follow a natural hierarchy involving other individuals' mind states. For example, in the play Othello, Shakespeare manages to keep track of five separate mental states: he intended that his audience believes that Iago wants Othello to suppose that Desdemona loves Cassio. Being able to maintain five separate individuals' mental states is the natural upper limit for most adults."

In that example, the five mental states belong to Shakespeare himself, the audience, Iago, Othello, and Desdemona. Shakespeare's tremendous grasp of what both the audience and all his various characters were thinking at any given moment is part of what gives his plays their power. But what about the rest of us? The researchers scanned the brains of forty volunteers while asking them to list all the people they had had social contact with in the previous seven days - in other words, how many friends they had seen. Dunbar reveals the results:

"We found that individuals who had more friends did better on mentalising tasks and had more neural volume in the orbital frontal cortex, the part of the forebrain immediately above the eyes. Understanding this link between an individual's brain size and the number of friends they have helps us understand the mechanisms that have led to humans developing bigger brains than other primate species. The frontal lobes of the brain, in particular, have enlarged dramatically in humans over the last half million years."

The researchers were able to control one big variable in the experiment by only testing postgraduates of roughly the same age. Dunbar readily admits that there are a bunch of other facts that can determine how much social contact a person has, including spare time, personality, location, and even things as fundamental as gender. Still, according to Dunbar, there does seem to be a link between mentalizing ability and friendship size, and that ability can be traced back to the size of the orbital prefrontal cortex.

Proceedings of the Royal Society B: Biological Sciences. Image by Losevsky Pavel, via Shutterstock.