Bonobo apes have displayed a trait often described as uniquely human – helping strangers with no obvious expectation of receiving anything in return. The finding doesn't just confirm that bonobos really are our better selves, but sheds light on the origins of human altruism.
Simplistic interpretations of natural selection suggest we should only help others if they are our relatives, and therefore carry many of the same genes, yet most of us rely on the kindness of strangers, and complex societies could probably not work without it. Altruism in humans is given many explanations, and often claimed not to exist at all in animals.
Yet Dr Jingzhi Tan of Duke University put a hole in that theory four years ago by reporting bonobos will share food with strangers. In other words, this is not just the kindness to kin we are already familiar with, but a willingness to go out of their way to help members of the same species to which they have no connection – and who might even become competitors for resources.
Now Tan is back, with a new study published in Scientific Reports showing just how far the generosity of the species once called pygmy chimpanzees will go.
In the Lola ya Bonobo sanctuary in the Democratic Republic of Congo, Tan led 16 wild-born bonobos (mostly rescued orphans) one at a time into one of two rooms separated by a fence. A piece of apple hung from a rope so that the apes couldn't reach it, but could release a wooden pin causing it to drop into the other room.
Occasionally bonobos placed in this environment would climb the fence to release the fruit, even though this required them to stop playing with a toy they appeared to enjoy. When Tan brought another bonobo into the other room, the first bonobo was four times more likely to go to the effort of releasing the apple than when the second room was empty. Moreover, they didn't need to be asked, there was no difference in the rate of assistance when the set-up prevented the second ape from gesturing for help. There was also no difference based on the sex of the animals involved.
In the light of Tan's past research, these findings may appear predictable. After all, climbing a fence to release food you could never get for yourself is less of a sacrifice than sharing a treat that could have been all yours. Nevertheless, previous examples of food-sharing were with individuals the donor could interact with, while this work involved assisting someone sealed off behind a fence.
In a separate study, but revealed in the same paper, Tan showed that the phenomenon known as “emotional contagion” is as strong for bonobos with strangers as with members of their pack. As with humans, bonobos are more likely to yawn when they see others yawning, regarded as an indication of empathy or mutual identification. Tan showed that bonobos are just as likely to yawn when they see a video of a bonobo half the world away yawning as when shown one of a member of their own family.
The empathy may in part reflect bonobos' social structure, where females leave their birth group to join an unfamiliar one on adulthood and need to be able to form friendships quickly when they arrive.
Bonobos have developed something of a cult following as a result of reports of their equality between males and females, low propensity to violence, and their enthusiasm for wild and varied sex. They're also possibly our closest relatives, and provide insight into our ancestral behavior. As the paper notes, modern human societies require us to interact with strange individuals frequently. Without an “extensive circle of trust” this would be impossible.
Tan and his co-authors argue their studies are evidence for the “first impressions” hypothesis, in which bonobos, like humans, are keen to make a good introduction, inspiring them to generosity towards those they have only just met. They suggest future research should explore whether this is a trait evolved from our common ancestor with bonobos or, since it is not shared with other apes, evolved independently.