And then there are those who take their altruism a step further by becoming two-time organ donors. Tom O'Driscoll, 60, of Sugarland, Texas, is one of very few Americans who has donated organs to ...

So if a gene for altruism can cause an individual to help its sibling, it “knows” there is a 50% chance it is helping a copy of itself. This is exactly how altruism has evolved in many species.