The amygdala is a brain structure crucial for regulating emotions. But the size of the amygdala also reveals just how rich and varied a social life a person leads. The bigger your amygdala is, the bigger your social network.
This new research follows up on previous studies that had demonstrated a similar link between amygdala size and social complexity in primates. Researcher Lisa Feldman Barrett explains:
"We know that primates who live in larger social groups have a larger amygdala, even when controlling for overall brain size and body size. We considered a single primate species, humans, and found that the amygdala volume positively correlated with the size and complexity of social networks in adult humans."
It's a simple but powerful link: the more people you regularly interact with, the bigger your amygdala. Of course, before you start X-raying your amygdala to find out how many friends you really have - which I assume is what anyone would do when presented with this news, because I've already tried it twice - it should be pointed out that it's not necessarily positive relationships that are reflected by the size of the amygdala.
The researchers only discovered a link between the size and complexity of the social network and the size of the amygdala - attempts to control for other potential factors, such as life support or social satisfaction. But that one solid link was very strongly supported:
"This link between amygdala size and social network size and complexity was observed for both older and younger individuals and for both men and women. This link was specific to the amygdala, because social network size and complexity were not associated with the size of other brain structures."
What this really speaks to is the so-called "social brain hypothesis", which theorizes that our amygdalas evolved in part to deal with the complexities of human social life. This is more compelling evidence that fundamentally we are meant to be social animals.