If you don’t have many friends, a new study says maybe your brain just isn’t big enough to attract them.

University of Oxford anthropologist Robin Dunbar and his colleagues took brain scans of 40 volunteers, who also completed tests to determine how good they were at “mentalizing,” or understanding another person’s mental state — meaning they comprehended others’ goals, needs and reasoning.

People in the study then reported how many people they’d had social contact with during the last seven days (excluding professional interactions), which provided a loose estimate of the size of each volunteer’s social network.

The research, published Jan. 31 in the journal Proceedings of the Royal Society B, revealed people with larger social networks seem to have larger orbital prefrontal cortexes. This area of the brain sits right behind the eyes and is responsible for directing appropriate social behavior and interactions with others, and is especially associated with things like emotion and reward.

The relationship between the size of the orbital prefrontal cortex and the size of a social network was also explained by a person’s ability to envision other people’s thoughts and emotions.

“The size of the orbitofrontal cortex in particular determines how good you are at these mentalizing skills, and these mentalizing skills, in turn, determine the number of friends you have,” Dunbar told LiveScience.

But what’s not known is if big orbital prefrontal cortexes are innate, or whether they grow in response to having more friends.

“My analogy is that you don’t get to be [Rafael] Nadal or any great tennis player just by having the body to do it,” Dunbar said. “You have to spend eight hours a day, seven days a week on the court practicing. On the other hand, if you haven’t got the body to begin with, no amount of practice is going to turn you into Rafael Nadal.”

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