They are nicer to strangers than their own friends and family.
PROBLEM: Being "prosocial," or putting yourself out there and meeting people outside of your immediate group of friends, isn't common in non-human animals. Chimps, for example, are extremely aggressive toward strangers, and will even kill their neighbors. But bonobos are much more tolerant, to the point of being go-out-of-their-way friendly, which, in the wild, is rare. Just how willing are they to make friends? Enough to share their food (which, among all animals, is huge)?
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METHODOLOGY: One by one, 14 bonobos were placed in central enclosure, with a feast laid out before them. Two bonobos were locked in cages on either side of them. One was part of their in-group, and the other was a bonobo who they knew of, but to whom they had never been formally introduced. The bonobo could decide whether to keep all the food to himself, or to let one or both of the others in to share.
In other variations of this basic set-up, researchers at Duke tested to see whether withholding the motivations of social contact and recognition would affect the bonobos' sharing behavior.
RESULTS: Nine out of the 14 bonobos unlocked the stranger's cage and invited him in before their groupmate.
Most often, the third bonobo would eventually be allowed to share the food as well, but it would often be the stranger who, having been given access to the central enclosure, would then go let them in -- even though that meant he would then be outnumbered by two members of the same group.