Neurological basis of selfishness? Is there a neurological component to selfishness? 

Awhile back, I witnessed a mentally retarded person who was severely possessive of a water fountain, claiming it was "his".  
I've also seen toddlers exhibit this same behavior.  Is this a form of arrested development?
I'm not sure how constructive it is to think of it in terms of "components", because there are so many that contribute to selfishness: for example, you only feel your body's pain.  Food and sex only feel good to you when you're the one experiencing them.

Instead, it might be more constructive to look for components of selflessness and altruism, them being the exception.  And that, according to some, lies in kin selection.