A very interesting (but really very interesting) paper … the consequences are really important if the results get confirmed in the future. The authors found that the volume of the amygdala correlates in humans with the size and complexity of social networks. (I need to check how they quantified social networks … but well, I can not access Nature from this computer J ). One more role of the amygdala, which was already a central knob for a lot of emotional behavior, and now also become a key player in social behavior (thank you Anna for having pointed out this paper!).
Bickart KC, Wright CI, Dautoff RJ, Dickerson BC, Feldman Barret L (2011) Amygdala volume and social network size in humans. Nature Neurosci, 14:163-164.