How many friends do you have? What do they look like? Did you know that your amygdala determines the number and the looks of your friends? Recent researches have shown that amygdala volume correlates with the complexity and the size of a person's social networks. In another word, large amygdala equals more friends and larger social circles.
In addition, according to D Bzdok and his colleagues, larger amygdala makes you good at face recognition. It's also a major factor that helps you make more accurate judgement about people's faces. If you think you are good at remembering people's faces but don't have a large or complex social network, then try this Face Memory Test . If you did not get a great score on this test, then you know your amygdala is what's affecting your social behaviors. Do you have good friends? Ask your Amygdala!
http://www.nature.com/neuro/journal/v14/n2/full/nn.2724.html
http://www.mendeley.com/research/ale-metaanalysis-facial-judgments-trustworthiness-attractiveness/
This question you bring up is quite fascinating. I have a friend who seems to remember everyone he meets and when he walks around campus he continuously keeps bumping into people he knows. I wonder if its due to his social nature of being an outgoing guy,or maybe his face is easily recognizable to people. Either way, very cool correlation regarding the amygdala and friends.