As they reported this year in the journal PLoS One, Jingzhi Tan and Brian Hare of Duke University and their colleagues showed that bonobos, those chimpanzee kin much celebrated for their peaceable ways and their nondomineering males, may be alone among apes, if not among animals generally, in preferring to share food with strangers over friends and family.

When wild-born bonobos were placed in a room and supplied with treats like slices of apples and bananas, and given the choice of opening a gate to admit either a familiar or an unknown bonobo, the provisioned bonobo would lift the latch of the stranger’s enclosure and then push food in the unfamiliar ape’s direction as though saying, “Eat, eat!”

“The first time we watched this on a video, it was so shocking, like seeing an alien on Mars,” Dr. Hare said.

The researchers propose that bonobos use food gifts to expand their social network, which could enhance their own odds of survival and reproductive success.

“If I’ve got an established relationship with somebody, me sharing food won’t change that relationship at all,” Dr. Hare said. “But if it’s somebody I haven’t met before, why not get the new relationship off to a good start?”

But bonobo xenophilia has its limits. In experiments where the bonobos could allow strangers into a food room but could not interact with them physically, they didn’t bother opening the door. What good does it do me if you don’t know what a good friend I can be?