The world works based on self-interest. If something does not benefit us, or does not seem the 'greatest choice' to us at a specific instance of time, we would not do it. There is always some self-serving point. I may die for my child to see my bloodline continue, or I may die for a stranger because I feel my life somehow validated when it is used to save another. In any case, I do something because it is of immediate benefit--regardless of how skewed the logic I use may be. I help people because I genuinely want the human race to advance. This is self-serving. I donate money to charity because I believe it is better used there. This is self-serving. A creature that exists to serve itself is the most economical of all, and so these are the creatures that roam the Earth. We all serve ourselves. Again, this is not a bad thing.