Chimpanzees usually form friendships based on trust, which may have various evolutionary advantages, a new study suggests.

For the new study – led by Esther Herrmann and Jan Engelmann, both of the Department of the Developmental and Comparative Psychology at Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany – the researchers looked at fifteen chimpanzees from the Sweetwaters Chimpanzee Sanctuary in Kenya.

Dr. Engelmann said that the results of the study were surprising because normally the social lives of chimpanzees are depicted as ruled by competition, conflict, and dominance. However, the new research shows that chimps are actually able to form trust-based friendships, according to Engelmann.

At first, Dr. Herrmann and Dr. Engelmann looked at the chimps’ interactions, like mutual eating and grooming, to determine which pairs were ‘fiends’ and which were not. Then, the researchers came up with a trust game to demonstrate their hypothesis.

In the game there is a ‘trust rope’ and a ‘no-trust rope’ and each chimp can pull on either one of them. When a chimp pulls on the trust rope, a box, filled with bananas and apples, moves to the chimp’s partner. (note: bananas and apples are some of the chimps’ favourite foods)

After the partner eats half of the food, it has to make a decision: it either sends the other half back to its partner, which means that it is a ‘trustworthy’ chimp, or it keeps the food, meaning that it is an ‘untrustworthy’ chimp.

On the other end of the spectrum, the ‘no-trust rope’ lets the chimp have immediate access to a type of food that is not so tasty.

According to Dr. Engelmann, on one hand, the ‘no-trust rope’ option is a lot safer for the chimp, but it also provides low-quality food. On the other hand, the ‘trust rope’ option is a little more risky, since the chimps that pulls on the rope may be left with no food at all, but it contains high-quality food.

The researchers concluded that when the chimpanzees were friends, they were more likely to go for the ‘trust rope’ option and share the food with their partners. Relationships based on trust are very important, because they help individuals have more offspring, have lower stress levels, and increase their chances of survival, Dr. Engelmann said.

The findings were published January 14 in the journal Current Biology.

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