Well...I used to think that it probably didn't exist because I couldn't for the life of me come up with something that someone could do, that didn't have any benefit for themselves.
But then the other day I was thinking about the things I might put in a will (morbid, I know). And I was thinking...why do I care that these certain possesions go to this person? Or why do I really want to make sure that no one feels left out, and everyone is given something of mine if I die.
Because when you're dead, you're dead and you're not around to care who gets what. (Supposedly).
So that must mean that I'm worrying about who to give what and sharing things out between people, because I don't want them to get hurt. There's no benefit to me that I can think of. So that would seem totally altruistic.
Unless you count the good feeling it gives me now. But then, I'm not letting that affect me, I hope.