"Our study adds new evidence supporting the hypothesis that some of the behavioural diversity seen in wild chimpanzees is the result of social transmission and can therefore be interpreted as cultural," an international research team writes today in the journal PLOS ONE.
The findings suggest that the ability of individuals to learn from one another originated long ago in a common ancestor of chimpanzees and humans, the researchers add.
"This study tells us that chimpanzee culture changes over time, little by little, by building on previous knowledge found within the community," said Thibaud Gruber, a co-author of the study, in a statement. "This is probably how our early ancestors' cultures also changed over time."
Scientists already knew that chimpanzees in different groups have certain behaviours unique to their group, such as using a particular kind of tool. They suspected that wild chimpanzees learn those behaviours from other chimpanzees within their group, as scientists have observed in captive chimps. But they could never be sure.
The new study documents the spread of two new behaviours among chimpanzees living in Uganda's Budongo Forest. It shows that chimps learned one of them — the making and use of a new tool called a moss sponge — by observing other chimps who had already adopted the behaviour. Chimps dip the tool in water and then put it in their mouth to drink.
The other behaviour, picking up and re-using a similar tool called a leaf sponge discarded by another chimp, didn't appear to be learned by observing other chimps.
"We were incredibly lucky to be in the right place at the right time to document the appearance and spread of two novel tool-use behaviours, something that is extraordinarily rare in the wild," said Catherine Hobaiter, a lecturer in psychology at the University of St Andrews in Scotland.
Quebec researcher involved
The research team also included Timothée Poisot, a postdoctoral researcher at the University of Quebec at Rimouski; Klaus Zuberbuhler, a colleague of Gruber at the University of Neuchatel in Switzerland; and William Hoppitt at Anglia Ruskin University in England.
The first chimpanzee in the group ever seen making a moss sponge was "Nick," the 29-year-old alpha male — the top-ranked male in the group. Over the next six days, the researchers saw another seven chimps making and using moss sponges. In six of the cases, the chimps had recently watched another chimp making and using a moss sponge.
An analysis showed the chimps were 15 times more likely to start making and using a moss sponge if they had previously seen another chimp do it. That was not the case for the other new behaviour, re-using discarded leaf sponges.
The researchers acknowledged that while the chimpanzees appeared to learn to make moss sponges from other chimps, they weren't exactly sure how — whether it was by direct observation, or independently trying to come up with a similar design, for example. That means they don't necessarily learn in the same way as humans.
Thibaud also noted that there is a difference in what humans can transmit to one another compared to apes that allows human culture to be far more complex than that of apes.