More friends, Bigger brains

Specifically, people with more friends have a bigger orbital frontal cortex (the part of the brain just above the eyes). Research published in Proceedings of the Royal Society B posits that the cognitive skills (like empathy) we use for maintaining large networks of friends are dependent on this specific brain region. Furthermore, MRI images illustrated that, when asked to mentally list their friends (as opposed to just their business associates), participants with a bigger orbital frontal cortex also tended to have more friends and were better at the kinds of social skills that involve juggling large social networks.