How many Facebook friends do you have?

Pleased that you have 400 close friends on Facebook? Sad that you only have 51? Well according to evolutionary anthropologist Robin Dunbar we can only have about 150 meaningful relationships at most: our brains aren't big enough for more. The number was derived by comparing the size of groups that species live in with the size of the brain and then extrapolating to humans. Interestingly enough, some recent neuroscience points to a correlation between the size of the amygdala and people's gregariousness. The amygdala's importance for emotion and fear in humans is well known but it turns out that the bigger it is the more outgoing you are. It's a correlation only of course.