Do you believe in selflessness?

Selflessness is nothing more than putting others first, and, in the process, fulfilling yourself in some way. Even your example of being eaten by a lion (presumably for someone else) would give you some sense of happiness. People are wired to gain fulfillment by helping others, and by doing that we not only encourage them, we also encourage ourselves to help more people. If no one ever helped anyone, we'd all be very unhappy. There's no real way to avoid happiness helping people (unless you're an evil supervillain--MWAHAHAHA!).