Human infants prefer helpers, but adult bonobos prefer hinderers

Over the past couple of days, headlines about a new bonobo paper caught my eye:

"Unlike Humans, Bonobos Shun Helpers and Befriend the Bullies"

"Humans like Helpers, but Bonobos Prefer Bullies"

"'Laid-back' Bonobos Take a Shine to Belligerents"

My initial reaction to the stories was mixed. One one hand, I'm really glad we are moving beyond stereotyping bonobos as peaceful "hippy chimps" who are constantly having orgies and nice all the time. Bonobos can be aggressive, both to their bonobo conspecifics and sometimes human caretakers. They do have engage in a variety of sexual behaviors with all age and sex classes, but that sexual behavior is typically over in a matter of seconds. Much like humans and chimpanzees, their lives are full of complex social relationships that include friendship, fighting, and jockeying for power and position.

My bonobo bestie Susie, who lives at the Columbus Zoo,
taught me that bonobo social lives are just as rich and complicated as our own.

On the other hand... having survived both junior high and academia (so far), I certainly do not buy the idea that humans like helpers and shun bullies. I'm familiar with the study that elegantly demonstrates that human infants prefer "helpers" to "hinderers," but my personal experience with humans suggests that for older humans, such behavior is likely vary context-dependent. And having spent some time studying bonobos, I suspect that, like us, how they would react in such situations would also likely be context-dependent.

But to evaluate this evidence, I needed to read Krupenye and Hare's article. They did four experiments on bonobos from ages 4-19 at Lola ya Bonobo, a sanctuary in the Democratic Republic of Congo. In the first experiment, they repeated the study done with human infants, where a square and triangle with googly eyes help or hinder a googly-eyed circle in climbing up a hill. The bonobos could then reach for a food reward under a cut-out of the mean, "hinderer" or nice "helper." Overall, the bonobos exhibited a significant bias toward reaching to the hinderer cut-out for food. However, when adults (> 9 years old) and subadults were analyzed separately, this bias was ONLY significant for the adults. In control trials with non-googly-eyed helpers/hinderers, there was no bias toward others.

Figure 1 from Krupenye and Hare (2017). See caption for more detail.

In the next two experiments, bonobos watched humans act as helpers or hinderers, and then could reach out to either to take a food reward. In Experiment 2, the bonobo subjects watched a human playing with a stuffed animal and dropping it. The helper tried to return the toy, while the hinderer snatched it away. The bonobos could then choose food offered at the same time from either the helper or hinderer. In this experiment, there were no significant differences when all age groups were lumped together. However, when adults and subadults were analyzed separately, adults exhibited a significant preference for "hinderers", while subadults didn't.

Figure 3 from Krupenye and Hare (2017). See caption for more detail.

Experiment 3 followed the same protocol as Experiment 2, but they did four trials beforehand where the bonobos were just offered food from the same two people. If bonobos exhibited a preference for one person, that person was assigned the "helper" position. If bonobos exhibited no preference in the initial trials, the 'helper" position was assigned semi-randomly. Bonobos exhibited a significant bias toward shifting to take food from the "hinderer." However, only adults participated in this experiment.

Finally, in Experiment 4, they did another experiment with the googly-eyed shapes, only this time they showed one googly-eyed shape displace the other for position. Displacements, where one individual takes another individual's spot, is a demonstration of dominance in primates. Humans do this too, and bonobos should recognize the "displacer" as the dominant individual. Overall, the bonobos exhibited a significant preference for the dominant individuals. Like the first experiment, when adults and subadults were analyzed separately, only the adults exhibited significant results.

So what do these results tell us? I think Krupenye and Hare have nicely demonstrated that adult bonobos in a sanctuary setting prefer "hinderers" or dominant individuals. However, these results don't hold for the younger bonobos (ages 4-9). And that's where the comparison to humans fall short. We can't compare human infants to adult bonobos, and then conclude that this is a species difference. I suspect that this may be an age difference in both species, though there also may be greater variation depending on culture, personality, socialization, etc.

Female bonobo Unga grooms infant Jerry at the Columbus Zoo. Bonobo mothers invest heavily
in caring for their offspring, so orphans who lost their mothers may potential behave differently.

Additionally, I have some concerns about how rearing history and choice of actors may have affected results. The bonobos were orphans who typically arrived at the sanctuary around 2-3 years old. Before this, they most likely witnessed their mothers (and possible other group-mates) killed by poachers. They then may have been held in cages and poorly cared for before being confiscated. Then, they are nurtured primarily by Congolese women that work at the sanctuary, while having access to play with peers. Thus, all of the bonobo subjects have a history of early trauma that may potentially affect their interactions with both humans and other bonobos. The people acting as "helpers" and "hinderers" were both Congolese men who had never interacted with the bonobos before, and I think it's possible that their identity may be a factor that could affect bonobos choices.

Nonetheless, this is some fascinating research, and hopefully it will be replicated with chimpanzees and other primates. The full-text of the study is available online, and you can watch the supplemental videos to get a better idea of what the experiments looked like.