Bonobos will share some bread with strangers rather than with old friends, new research shows. The finding, led by Dr. Brian Hare, from Duke University, USA, was published online in the January 2 edition of PLoS ONE. Such behaviour has never been observed in non-human primates before and may help guide our understanding of how certain altruistic and social behaviors evolved in human ancestors. 

Bonobos are very social creatures, and researchers think this behaviour may help. "...they're trying to extend their social network," Dr. Hare said. It seems that for these species such social networks are just as important, if not more, as existing friendships. 

In their research, Dr. Hare's team experimented with a group of bonobos from the Democratic Republic of Congo. In one set of experiments researchers left food in a single enclosure, accessible by a door leading to two more enclosures, each hosting a bonobo. The bonobo in the food-laden enclosure could open the door to either one of the outside enclosures. One bonobo was known, the other was a stranger. Almost all the bonobos opened the door to share food with the stranger. Often, a third animal was offered food, as well. 

In a second experiment, the bonobo controling the door wouldn't get any food, even if it allowed a strange animal to get food. Nearly all the animals helped the stranger anyway, as it would allow them to secure a new social contact.

The only time the bonobos would not share with strangers was when they would have no social contact, but could get the food. This was the first experiment where the bonobos had no social benefit of sharing. The care bonobos showed for others still had an element of selfishness to it: no benefit, no sharing. This last experiment illustrated one key difference between most humans and bonobos. While both species will share with strangers, only humans will do it anonymously, without immediate social benefit.