Are all of our actions motivated by our selfish nature?

Sure, there are the obvious things: making money, self-entertainment, sex, but even things we supposedly do for others are selfish to a degree. We serve others because we want to be good people, so these acts make us feel better. We even help others at our own expense for the same reason-- to be good people. Even our obligations are selfish to an extent. We did chores, for example, because it was in our best interest in the long-term, not just because it was a necessity.

Is it possible to commit a fully selfless action? Are we, by definition, completely selfish beings?