Here's something I did recently: signed up to be a marrow donor. I'd like to say I did it for all kinds of altruistic reasons: generosity, caring, that sort of thing. I mean, I've been an organ donor since I got a driver's license, my family knows my feelings about that and agrees with me that if any part of me is useful after I stop needing it, take it away, doctors.
And I have genetics that reach into central Asia, which is where the banks have limited matches and are always looking for more. Maybe I could say I joined the registry because they needed me.
But I really did it for selfish reasons. I'll never meet anybody who gets my liver, or my heart, or my corneas with their superhuman vision. But if you donate marrow, you might get to meet the recipients. You might get to meet their families. They will have your blood inside them (their blood changes to your blood type!).
I hope I never need to go to the marrow registry. But I also hope that the swabs I sent in last week are a match for somebody, and I can help save a life.
(And yes, I do give blood, but that's a totally selfless donation. I wanted to do something a little more selfish, too.)