I highly doubt 40% of people here are altruistic. Because if you were doing it for ego or real world reward, wouldn't it make sense to vote for altruism then comment and tell everyone about it? Also I just don't think there are that many selfless people.
Me? I said "shrug" because I don't do that many good deeds, and when I do, it's because I've got nothing better to do or it's not much difficulty on my part or I know they will pay me back/ego. Mixture of everything.
Seeing a lot of people telling us about their anonymous donations and selfless good deeds. Sort of defeats the purpose of "anonymous" when you tell everyone, that's a reward, even if it's not monetary. No shame in it though, it's human nature.