Humans are known to possess the trait of sharing with others, including strangers. It was thought that sharing is a feature unique to humans developed from social networks, the ability to use language, warfare and/or cooperative breeding.

Now, a new study by researchers from Duke University has found that bonobos, one of the closest relatives to humans, also have an inclination to share with other animals. But, they prefer to share their food with strangers before sharing with an animal they know well, in a bid to extend social interactions.

"It seems kind of crazy to us, but bonobos prefer to share with strangers," Brian Hare, a professor of evolutionary anthropology at Duke University, said in a statement.

"They're trying to extend their social network. And they apparently value that more than maintaining the friendships they already have."

For their study, Hare and his team carried out a series of experiments with bonobos living in the Lola ya Bonobo sanctuary in Kinshasa, Democratic Republic of Congo, to measure their willingness to share.

The first experiment involved three bonobos in three different enclosures adjacent to each other. The bonobo in the central enclosure was the test subject. One of the other two enclosures had a bonobo that the test subject knew from their group and the other enclosure had a stranger. The test subject had the knowledge to open a door to either of the other two chambers, or both.

When a pile of food was placed, the test subject had the option to eat the food all for itself or invite one of the other bonobos to share.

In more than 70 percent of the trials, the bonobos shared their food at least once. They preferred to release the stranger first and share their food. The third bonobo was also often allowed to share, but in most cases it was the stranger, and not the test subject, that opened the door, reports

Further experiments showed that the bonobos chose to open and release the stranger or the acquaintance to reach the food even if it was not able to access the food or contact the other animal for social connections.

But the surprising part was revealed when researchers conducted their final experiment. This time, the test subject was given access to the food and to share it with the other animal, but was not allowed to interact socially with the stranger or the friend. In this case, the animal chose not to share its food as it did not receive any social contact.

"They care about others," Hare said, adding, "They'll share when it's a low-cost/low-benefit kind of situation. But when it's a no-benefit situation, they won't share. That's different from a human playing the dictator game. You really have to care about others to give anonymously."

The findings of the study appear online in the open access journal PLOS ONE.