Trust does not seem to be unique to humans and may have a long evolutionary history, according to a study in chimpanzees.

Credit: Esther Herrmann

Jan Engelmann and Esther Herrmann at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, identified captive chimps (Pan troglodytes) that were friends with each other — individuals that frequently groomed and spent time together. The animals were then paired up and each chimp was presented with a choice of two ropes that it could pull. The 'no-trust' rope gave the chimp a small food reward and left the partner empty-handed. The 'trust' rope gave the partner a reward, part of which could be sent back to the other chimp.

Chimps were more likely to choose the trust rope when paired with friends than with non-friends, showing that trust in close relationships is not unique to humans. The characteristic might have evolved to stabilize social bonds in primates, the authors say.

Curr. Biol. (2016)