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.