Despite a reputation as mellow apes, bonobos have a thing for bad guys.
Rather than latching on to individuals with a track record of helpfulness, adult bonobos favor obstructionists who keep others from getting what they want. The result may help explain what differentiates humans’ cooperative skills from those of other apes, biological anthropologists Christopher Krupenye of the University of St. Andrews in Scotland and Brian Hare of Duke University report online January 4 in Current Biology.
Previous investigations indicate that, by 3 months old, humans do the opposite of bonobos, choosing to align more frequently with helpers than hinderers. Humans, unlike other apes, have evolved to seek cooperative partnerships that make large-scale collaborations possible (SN: 10/28/17, p. 7), Krupenye and Hare propose.
“Conducting similar experiments with chimpanzees and other apes is a key next step,” Krupenye says. If chimps view hinderers as kindly as bonobos do, that finding would support the duo’s proposal about human cooperation, he says.
Bonobos may view those who impede others’ actions as socially dominant and thus worth grooming as allies, Krupenye says. Although bonobos readily share food, social pecking orders still affect the animals’ behavior.
The researchers showed 24 bonobos four animated videos featuring pairs of colored shapes, most depicted with a pair of eyes. In one video, a circle tries and fails to climb a hill until a “helper” triangle arrives and pushes the circle to the top. In a second video, a circle tries and fails to climb a hill before a “hinderer” square arrives and pushes the circle farther down the hill. In the other two videos, other shapes with eyes push an eyeless, unmoving circle up or down a hill.
After watching the first two videos, bonobos chose between paper cutouts of helper and hinderer shapes placed on top of small apple pieces. The same choice was presented for cutouts of shapes from the last two videos.
Snacks covered by hinderer shapes were chosen about 70 percent of the time by the 14 adult animals, ages 9 and older. Younger bonobos displayed no strong preference either way. Apes of all ages showed no partiality to either shape that had pushed inanimate circles.
Adult bonobos also reached more often for an apple piece offered by a human they had observed snatch a toy dropped by another person, versus a human they had seen return the toy.
In a final experiment, eight of 24 bonobos usually selected apple pieces covered by cutouts of an animated shape that the apes had seen win a contest with another shape to occupy a location. This result suggests that some bonobos’ strong preference for dominant individuals partly accounts for the newly reported fondness for hinderers, Krupenye says.
“The notion that bonobos approach the bully because they view that individual as more dominant is a very plausible interpretation,” says psychologist Felix Warneken of the University of Michigan in Ann Arbor. Warneken, who did not participate in the new study, studies cooperative behavior in human children and nonhuman apes.