WHAT was the basis for the earliest friendships? If wild chimps are any guide: support in a fight, borrowing a valued tool, and a bite to eat now and then. Quite similar to our friendships today, in fact. Indeed, some chimps are so modern they have relationships that we would classify as friends with benefits.

Primatologists are reassessing the complexity of chimpanzee society in the light of new findings that also suggest answers to a long-standing question: why share things with non-relatives?

For the first time wild chimps in Senegal have been observed taking plant foods and tools from other chimps, who don’t react to the intrusion. The chimps donating their stuff don’t get paid, but neither do they protest. Instead, the trade appears to help build social cohesion.

What’s more, in another west African study, this time in Ivory Coast, a “market” has been described where chimps exchange commodities in the shape of both social behaviours including grooming and sex, and resources such as meat.

Christophe Boesch of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, says we have only recently begun to appreciate the time and energy chimps invest in reciprocal relationships, and he compares chimp relationships to friendship. “These findings have prompted primatologists to use some terms that have in the past been reserved for humans.”

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