Nearly 150 years ago, Charles Darwin proposed that morality was a byproduct of evolution, a human trait that arose as natural selection shaped man into a highly social species—and the capacity for morality, he argued, lay in small, subtle differences between us and our closest animal relatives. “The difference in mind between man and the higher animals, great as it is, certainly is one of degree and not of kind,” he wrote in his 1871 book The Descent of Man.
For the last 30 years, the psychologist Michael Tomasello has been studying those differences of degree, trying to determine how our species’ social nature gave rise to morality. The co-director of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, Tomasello has spent much of his career conducting experiments that compare the social and cognitive abilities of chimpanzees, our closest relative in the animal kingdom, and human toddlers. In his forthcoming book A Natural History of Human Morality, he draws on decades’ worth of work to argue for the idea that humans’ morality, unique in the animal kingdom, is a consequence of our tendency to collaborate and cooperate in ways that other great apes do not.
Beginning in the early 20th century, research on non-human primates—like chimpanzees, bonobos, and orangutans—has shown that they are capable of many things once considered uniquely human, like tool-making, empathy, discerning the intentions and goals of others, and forming friendships. But humans also have language, laws, institutions, and culture. For a long time, the dominant explanation for these uniquely human concepts was our raw intelligence—the human brain is three times larger than the chimpanzee brain—but in recent years, some scientists have also argued that our more social nature may be what’s allowed us to advance so much further than the apes.