Though we share more than 95 percent of our DNA with these apes, many people think that morality is a uniquely human creation. The prevailing and enormously influential view for hundreds of years—championed by intellectual giants from John Locke, Sigmund Freud, and Jean Piaget—was that human beings are born as blank slates and acquire knowledge about right and wrong through their parents, teachers, and other civilizing engines of culture.

Another idea, equally influential, is what the primatologist Frans de Waal calls veneer theory. Veneer theory, which arises from a botched up understanding of Darwinian natural selection, holds that morality is "a cultural overlay, a thin veneer hiding an otherwise selfish and brutish nature,” as de Waal explains. Nature is red in tooth and claw so the point of civilization is to tame the inner beast that lurks inside each of us.

But over the last decade, a growing body of evidence has challenged both the blank slate view of morality and veneer theory. Morality, it seems, is hard-wired. Chimps, who lack the tools of civilization, have the building blocks of morality and moral goodness. Primatologists like Frans de Waal, Jill Pruetz, and Christophe Boehm have shown that our closest kin in the animal kingdom, from chimps to bonobos, treat each other with empathy, compassion, and self-sacrifice. Macaque monkeys, more distant from us on the evolutionary chain than the great apes, won’t take food if doing so causes another monkey harm. Even rats show empathy. “Faced with a choice between two containers, one with chocolate chips and another with a trapped companion,” writes de Waal in his recent book about the origins of morality, The Bonobo and the Atheist, rats often choose to rescue their companions first.

Through studying the emotions and behaviors of animals, Darwin himself concluded that they are quite capable of sympathy, affection, and altruism. He wrote about one dog who wouldn’t pass by a sick cat without licking it a couple of times. Dogs, like chimps and humans, also follow social rules that keep the peace in the community. Darwin thought that it is from their social instincts that morality arises. “It would be absurd to speak of these instincts as having been developed from selfishness,” he wrote.

Studying animals is one way to learn about the origins of morality, but another is of course to look at baby humans. Human babies, before they learn how to speak and even hold up their own bodies, are capable of not only telling the difference between right and wrong, but of making morally fraught decisions, a finding that shocked scientists when it was uncovered about ten years ago.

“It knocked our socks off,” says Yale’s Paul Bloom, one of the psychologists behind a series of groundbreaking studies of infant morality and the author of a fascinating new book, Just Babies: The Origins of Good and Evil. It turns out that babies, who are too young to have learned about morality, have an innate moral sense. On top of that, they show a basic disposition to goodness. They are not the little monsters that veneer theorists thought they were. Without prodding, for instance, infants start sharing after they’re six months old. When they’re a little bit older than that, toddlers will help a stranger in need.