Chimp friends
Chimps are more trusting of their friends than strangers, just like humans patries71/Flickr

Just like humans, chimps build their friendships on trust. A new study shows they are much more trusting of their friends, than those they do not know as much.

The research tested the chimps' trust by offering them two different types of food. They either had the option to share their favourite type of food, which resembles trust, or take a whole portion of an average food for themselves, because they did not trust the second chimp to share with them.

"We were very surprised by our findings since some researchers depict chimpanzee social life as dominated by conflict, competition, and dominance," Jan Englemann, a researcher on the study, told IBTimes UK. "Our research suggests that chimpanzees are able to form friendships that are based on trust; so chimpanzees, like humans, show trust-based co-operation."

The results suggest human friendships are not so unique. They are as a result of evolutionary history that goes back further than anybody believed.

To test their theory, the researchers from the Max Planck Institute for Evolutionary Anthropology analysed 15 chimpanzees over a five-month period, and published the results in Current Biology. Initially, they made assumptions on each chimp's friends, based on their grooming habits, contact, whether they ate together, and even whether they just spent time with each other. They were subsequently grouped as "friends" or "non-friends".

Scientists then carried out an exercise whereby each chimp had the opportunity to show their trust to either a friend, or a non-friend. They could decide whether they wanted to give a second chimp a large portion of their favourite foods – which in turn their team-mate would deliver half of it back to them – or take a portion of a lesser-liked food all to themselves, because they did not believe the other chimp would share when they received the spoils.

The results showed that chimps were far more likely to choose sharing their favourite foods with their friends. Likewise, more often than not, they would choose the alternative when dealing with a non-friend.

"Research with other primates – baboons – has shown that friendships entail important evolutionary benefits," Englemann said. "Individuals with friends live longer, have more children, and lower stress-levels. I can imagine that the same benefits apply to chimpanzees. So forming trusting, long-term relationships was probably selected for by natural selection."