Once each individual is healthy and happy (his basic needs are met) he can reasonably choose (not being effected by extreme emotion of fear and pain) to choose what it takes to build a system that automatically produces those basic human needs.  The more effective one is at this; the more abundance one has to share. And so on...  We work together for the advantage it has in being most effective at creating abundance for all involved.  Abundance is why we become generous.  Ever wonder why The United States is the most generous country that has ever existed?