Why is selflessness part of our nature?

It's probably just part of our drive to survive, but we also have a very strong drive to protect our offspring, which might be stronger than the desire to survive. I don't think my husband or I would eat anything before our children if they were hungry. Having children is the most selfless thing a person can do, and I know many parents who would give their lives for their kids without a second thought. We are selfish because selfishness makes the world go around. It keeps our economy going all that.