Is helping others a moral obligation?

A few months ago, we were debating in our Debate and Speech club about "it is a moral obligation to help those in need". I recently read a book by Dalai Lama "The Road to Happiness" I believe, in which this "issue" came back again. Are people born selfish? Can they change? Are people altruist? Can we help others? Should we help others? In case we do, is it because of the good feeling we get, or just because we want to help them? Can this be confused with weakness?