Selfism
The holy grail of the physical sciences is the grand unification theory - one that would reconcile the four forces of the known physical universe. Its counterpart among the social sciences would reconcile altruism and selfishness. Such a theory exists. It is simple. It is obvious. And it accommodates those who argue for the uniqueness of homo sapiens without rebuking the underlying assumptions of classical darwinism.
Humans are unique, of course - in degree, if not in kind. We are enormously smarter than the next contender down the food chain. For this reason, we know we harbour another attribute that may be unique among living organisms: we have the ability to operate at a level beyond mere physical survival. We have the capacity to do more than just survive. We have the capacity to thrive.
Survival is a function of sustenance. So long as we have adequate food and water (and a modicum of protection against predators and the elements) there is no theoretical barrier to one’s ongoing perpetuity other than the eventual expiration that seems to afflict all living entities. However, to thrive we need something more. Something intangible. Something conjecturally essential to survival itself. It is commonly called nurturance.
Where does nurturance come from? Primarily, it derives from positive interaction with other living entities ... principally, other humans. It is characterized by the indefinable (but unmistakable) sense of inner satisfaction that invariably accompanies such interaction. Perhaps it is simply a manifestation of perceived self-affirmation on the part of the only species (so far as we know) capable of appraising its own existence. Whatever the dynamics, nurturance is largely within the control of the individual: the more one invests in others, the more nurturance one tends to experience as a result.
Viewed this way, the phenomenon of investing in others is not at all selfless. Quite the contrary. Sooner or later, unencumbered by precept or example, any otherwise functional human not struggling with elementary survival is bound to behave in this fashion out of self-interest.
In this, as in so many regards, semantics can get in the way. The word selfish carries a lot of baggage. A more useful term might be selfist. Accordingly, altruism is simply selfism writ large.
One remarkable characteristic of this phenomenon is that one’s investment in others need not be reciprocated (or even acknowledged) to be nurturing. Indeed, it doesn't even require independent substantiation. An anonymous benefactor feels the positive inner glow notwithstanding the absence of attribution. In fact, so long as there is the potential for benefit (and no practical prospect of harm) any such conduct can be understood in terms of selfism. Even the unlaurelled nameless blood donor can be nurtured by the act of giving - despite the possibility that the blood donated might never be used.
Insofar as this analysis withstands scrutiny, it may offer some hope for our smart - but struggling - species. Imagine seven billion people tripping over one another in their mutual haste to do acts of kindness because they’ve finally grasped the fact that it is in one’s individual self-interest to do so.