““7. The principle of reciprocal altruism—I’ll scratch your back if you’ll scratch mine”—is universal; people do not by nature give generously unless they receive something in return, even if what they receive is social status. 8. The principle of moralistic punishment—I’ll punish you if you do not scratch my back after I have scratched yours—is universal; people do not long tolerate free riders who continually take but almost never give.””
