Touching, embracing and kissing before stressful events may be an ancient way of building trust, according to scientists studying the behaviour of our closest ape relatives.

Researchers at Durham University studied chimpanzees and bonobos using physical contact to reassure each other ahead of conflicts over food.

One of the most surprising findings was that chimpanzees, despite their reputation for aggression, engaged in close contact, including placing fingers in one another's mouths.

"Before stressful events, they come together, they reassure each other, they touch each other, they hug each other," said Prof Zanna Clay.

She described the behaviour as "a rallying cry" before a stressful event, much like a football huddle before a big match.

"It's like a 'we' rather than a 'me'," she said.

The experts studied chimpanzees and bonobos living at two great ape sanctuaries in the Democratic Republic of Congo and Zambia.

They designed an experiment to mimic natural feeding in the wild - using peanuts.

Use of touch to build trust and cooperation

The apes were observed during the five minutes before the peanuts arrived, when they knew food was coming.

Researchers recorded instances of reassuring physical contact, including touching, embracing and kissing.

The team found that individuals who touched and hugged were more likely to access food and eat alongside each other peacefully.

More tolerant groups showed higher levels of reassuring touch, including what researchers described as "reassurance trains", in which multiple apes embraced one another in succession.

"Comparing bonobos and chimpanzees - our two closest relatives - offers fascinating insight into the evolutionary roots of social behaviour and how they, and we, manage tension, competition and cooperation," said Dr Jake Brooker.

He said social touch was one of the oldest forms of communication and likely predated language.

The researchers say the use of touch to build trust and cooperation may date back at least seven million years, before humans, chimpanzees and bonobos split from a common ancestor.

So when humans gather in a football huddle, hug a teammate or offer a pat on a shoulder before a stressful event, they may be drawing on a social toolkit that is millions of years old.

The research is published in the journal, Proceedings of the Royal Society B: Biological Sciences.