The Altruism Equation, by Lee Alan Dugatkin
r = genetic related-ness
b = benefit
c = cost
That's the rule William Hamilton figured out in 1964 to explain altruistic behavior. It's been tested and upheld in many experiments and studies since.
Humans, of course, have Reason and can overcome genetic heritage, but I think we're generally foolish to try. That is, we should not try to overcome our tendency to love our family (unless they prove themselves unlovable), nor should we expect altruistic acts of others outside of their families.
Quicky thoughts. I can't imagine I'll stop thinking about this, so you can expect more on it when I have time.
One thought right now: families are natural - institutions aren't. I see a use for this knowledge in the Homeschooling movement.