Editor's Note: This post is the last in a four-part series of essays for Scientific American by primatologist Frans de Waal on human nature, based on his ongoing research. (The first post, on our sense of fairness, can be read here; a second post, on the impact of crowding, is here; and a third post on power and coalitions is here.) De Waal and other researchers appear in a series of Department of Expansion videos focusing on the same topic.

The origin of human aggression and warfare remains hotly debated. Until now, this debate has been dominated by what chimpanzees do and how this compares with our own species. It is little known, however, that we have an exactly equally close primate relative, the bonobo. This species makes Hobbesians very uncomfortable, so they do everything to marginalize it. One anthropologist seriously suggested that we should ignore bonobos, because they are close to extinction, not realizing that by the same token we should also ignore "Lucy," "Ardi" and all those other ancestors that bit the dust. Others treat bonobos as a wonderful afterthought, a great curiosity, but irrelevant to where we come from.

The first study to compare bonobos and chimpanzees was carried out at the Hellabrunn Zoo in Munich. German scientists made a list of differences between both species, including the bonobo's sensitivity, peacefulness and obvious sex drive. If these differences were already known in the 1950s, one might ask: Why was the bonobo absent from the debates on human aggression, and still is? Well, that study was published in German, and the time that English-speaking scientists read anything other than English is long past. Another reason is cultural: Victorian attitudes prevent most American or British scientists from touching the bonobo's eroticism. In the 1990s a British camera crew traveled to the remote jungles of Africa to film bonobos only to stop their cameras each time an "embarrassing" scene appeared in the viewfinder. And National Geographic never published the explicit bonobo pictures brought home by one of its photographers (which were subsequently put to good use by this photographer, Frans Lanting, and myself in Bonobo: The Forgotten Ape).



But far more important is the fact that bonobos fail to fit established notions about human nature. Believe me, if studies had found that they massacre one another, everyone would know about bonobos. Their peacefulness is the real problem. I sometimes try to imagine what would have happened if we'd known the bonobo first and the chimpanzee only later—or not at all. The discussion about human evolution might not revolve as much around violence, warfare and male dominance, but rather around sexuality, empathy, caring and cooperation. What a different intellectual landscape we would occupy!

Bonobos act as if they have never heard of the killer ape theory that remains popular in anthropological circles. Among wild bonobos there's no deadly warfare, no male dominance, and enormous amounts of sex. They make love, not war. Science had more trouble with them than a 1960s family had with its long-haired, pot-smoking black sheep who wanted to move back in. They turned off the lights, hid under the table and hoped that the uninvited guest would go away.



Frans de Waal, PhD, is a Dutch-American primatologist known for his popular books, such as Chimpanzee Politics: Power and Sex among Apes (1982) and The Age of Empathy: Nature's Lessons for a Kinder Society (2009). He teaches at Emory University in Atlanta where he directs the Living Links Center at the Yerkes National Primate Research Center. He has been elected to the National Academy of Sciences and the Royal Netherlands Academy of Arts and Sciences.

The views expressed are those of the author and are not necessarily those of Scientific American.

Video credit: Department of Expansion