"Another ridge includes social interaction schema. Some of these schema may have aspects that go far back in evolutionary time, such as those involved in detecting predators and seeking protectors, or that govern direct "tit-for-tat" reciprocity (you scratch my back, and I'll scratch yours; if you bite me, then I'll bite you). Other social interaction schema may have elements common to some species of social mammals (e.g., bats, wolves, monkeys, and apes). Examples include certain systematically recurrent forms of delayed reciprocity (you help me now and I'll help you later), indirect reciprocity (I'll help those who help those who help me; the enemies of my enemies are my friends), and greeting displays of submission-domination. Still other social interaction schema appear to be unique to humans, such as making decisions to cooperate on the basis of social signs of reputation rather than on the basis of individual observation and experience, or in offering and obtaining future commitments of an indeterminate nature (when the chips are down, I'll help you, whatever the situation). Only humans, it appears, willingly commit their lives to groups of nonkin."