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?
Wilson's group selection: Under certain circumstances, groups of cooperators can out-compete groups of non-cooperators, thereby ensuring that their genes — including the ones that predispose them to cooperation — are handed down to future generations.
Complexity isn't the issue. It's simply a matter of having the genetic predisposition to be able to function as part of a group. Of course, functioning as part of the group may be easier if you also share the same instinctual responses typical of your group. With humans, we instinctively feel ick about cannibalism, incest, spoiled meat, etc. We are also tribal and territorial. I think altruism, like tribalism, is instinctive and evolved in response to the group needs, even though the selection for these traits was at the level of individuals. In human society, the maladapted, the sociopath, is a monster to be shunned or killed. The maladapted don't prosper in the long run, even though they may gain temporary advantage by stealing or avoiding responsibilities.
Seems simple to me.
Rare exceptions to the rules. It sounds like you might have another idea to explain altruism, or, at least, some of the strong and rather universal biases we feel.