The currently accepted explanation for altruism is something known as kin selection theory. It says that an organism trying to pass its genes down to future generations can do so indirectly, by helping a relative to survive and procreate. Your brother, for example, shares roughly half your genes. And so, by the dispassionate logic of evolution, helping him produce offspring is half as good for you as producing your own. The full story follows.
For the last thirty or more years, kin selection theory has been the generally accepted explanation. I was never comfortable with it, seeing evolution as a struggle between individuals, not tribes. Someone else seems to be at odds with the standard model. I'm not sure if Dr. Wilson is on the same track I am, and I may be totally off the wall, but I'll throw my working model out and let the pros tell me what's wrong with my simplistic model.
I was watching the meerkats (very sociable beings) at the local Busch Gardens zoo recently. The usual question that pops up is, why does the lookout risk him/herself, standing on the top of the tallest pile of dirt, watching and sounding an alert if needed? They do seem to take turns at it but, still, why take the risk?
It occurs to me that if he or I weren't playing our parts in our particular cultures, and I see his and mine both as largely instinctual, we'd have a hard time getting dates. Seriously. Does being a sociopath give an individual an evolutionary advantage? I don't think so. Those of us who can better adapt to the needs of our group do better, all other things being equal. What am I missing?