"More recently, however, primatologists have conducted controlled laboratory experiments that strengthen the case for genuine caring in nonhuman primates. In a series of experiments, Felix Warneken, Michael Tomasello, and their colleagues have demonstrated that chimpanzees will help both other chimps and humans spontaneously, and without expectation of a reward. In one experiment, chimps spontaneously volunteered to help a human experimenter by retrieving an out-of-reach object for him. In another experiment, chimps performed similar good deeds for an unfamiliar human, even when doing so required climbing over obstacles. In yet another experiment, chimps actively chose to release a chain, thus granting another chimp access to food while gaining nothing for themselves. It seems that neighborliness goes even further down our evolutionary tree. Recent studies by Venkat Lakshminarayanan and Laurie Santos show that capuchin monkeys, given a choice between rewarding themselves only and rewarding themselves and a neighbor, typically choose to do the neighborly thing, even when the neighbor's reward is bigger. There is even evidence of empathy in rats, who will forgo an immediate reward in order to free another rat from a restraining device.
"In sum, we are a caring species, albeit in a limited way, and we probably inherited at least some of our caring capacity from our primate ancestors, if not our more distant ancestors. We care most of all about our relatives and friends, but we also care about acquaintances and strangers. Under ordinary circumstances, we're highly reluctant to harm strangers, so much so that even pretending to do so causes our veins to constrict. We're also willing to help strangers, expecting nothing in return, so long as it's not too costly. Because we care about one another, because our individual payoffs are not the only ones that matter to us, we can more easily get ourselves into the magic corner."