There's actually a lot of evidence in primates and other animals that they return favors.
Frans de WaalWe start out postulating sharp boundaries, such as between humans and apes, or between apes and monkeys, but are in fact dealing with sand castles that lose much of their structure when the sea of knowledge washes over them. They turn into hills, leveled ever more, until we are back to where evolutionary theory always leads us: a gently sloping beach.
Frans de WaalMorality, after all, has nothing to do with selflessness. On the contrary, self-interest is precisely the basis of the categorical imperative.
Frans de WaalBonobo studies started in the '70s and came to fruition in the '80s. Then in the '90s, all of a sudden, boom, they ended because of the warfare in the Congo. It was really bad for the bonobo and ironic that people with their warfare were preventing us from studying the hippies of the primate world.
Frans de Waal