Given a choice, most humans would rather spend their time with nice people and avoid befriending jerks. Developmental psychologists have even found that by three months of age, human infants can tell the difference between the two—and seem to prefer those who help to those who hinder. According to a study published Thursday in Current Biology, the opposite seems to be true for bonobos.
“Of our two closest relatives, chimps and bonobos, [bonobos] are the ones known to show less extreme aggression. They’re socially tolerant in food settings, and they share food and cooperate in ways chimpanzees might not,” says Duke University evolutionary anthropologist Christopher Krupenye (now at the University of Saint Andrews in Scotland), who led the study. “So we thought if either of them are likely to share with humans this motivation to prefer helpers, it may be bonobos.”
Together with Duke University anthropologist Brian Hare, Krupenye tested a group of 43 bonobos living in a sanctuary in the Democratic Republic of the Congo. The researchers used a range of experiments designed to see whether bonobos, like human infants, can distinguish individuals according to their social behaviors—and whether they prefer the helpers, like we do.
In one experiment 24 bonobos of various ages watched a series of cartoons involving three different animated shapes. The video depicts an anthropomorphic circle trying to ascend a hill. In some cases the circle is helped up the hill by a triangle; in others, a square prevents the circle from reaching the summit. The apes were then offered two identical pieces of fruit—one underneath a paper cutout resembling the “helper” triangle, the other beneath the “hinderer” square. Like human infants, bonobos could distinguish each individual on the basis of its social behaviors. But unlike human infants, they preferred the square.
In the next pair of experiments the bonobos watched a series of skits in which a lost toy was either retrieved and returned by a human helper or stolen by a hinderer. As before, the bonobos opted to accept food offered by the hinderer rather than the helper.
The original infant studies were not intended to see whether the subjects favored the helpers but rather whether they could distinguish between moral and immoral acts in the first place, says University of Southern California developmental psychologist Henrike Moll, who was not involved in the new study. That they preferred the “good guy,” she explains, “was almost a presupposition.” The results from the bonobos experiments reveal the same discrimination abilities, Moll notes—“but because of the fact they prefer the bad guy, I think it opens up the possibility that they might be viewing this completely differently.”
Krupenye showed the bonobos a final set of videos that involved animated shapes competing for access to a part of the screen, with one shape repeatedly displacing the second. Even without the added moral complexity, the bonobos preferred the food associated with the dominant shape. And when the researchers looked at the results more closely, they saw the preference patterns in all four experiments were driven by the adult bonobos (nine years or older) whereas the juveniles and adolescents (four to nine years old) did not show any clear preference.
Behaviors we humans see as antisocial might, in bonobo society, be more reflective of social dominance—something that would be of particular interest to the adults. For apes living in a strict social hierarchy, it pays to befriend those on top because this could mean better access to food, mates and other perks. Indeed, bonobos have been seen begging high-ranking individuals for food, even when they could easily have gotten it on their own elsewhere, as if they continually need to reaffirm their place on the social ladder as well as reassure the dominant ones they know who is in charge.
Krupenye says his team’s results support the notion that the preference to avoid individuals who mistreat others is one of the things that sets humans apart from other apes. But Moll argues it may not make sense to compare the two species on the basis of their reactions to these videos, especially if humans are motivated to interpret them in terms of morality whereas bonobos view them through the lens of social dominance.
As is so often the case in studies that compare multiple species, the outcomes of these experiments result in more questions than answers. “Right now, we can say we see that bonobos and human infants show opposite preferences,” Krupenye says. More research will be necessary, he notes, including with chimpanzees, to tease apart exactly what that means.