Thibaud Gruber
By Sam Wong
Six years ago, a chimpanzee had the bright idea to use moss to soak up water, then drink from it, and seven others soon learned the trick. Three years later, researchers returned to the site to see if the practice had persisted to become part of the local chimp culture.
They now report that the technique has continued to spread, and it’s mostly been learned by relatives of the original moss-spongers. This adds to earlier evidence that family ties are the most important routes for culture to spread in animals.
After the first report of chimps using moss as a sponge in Budongo Forest, Uganda, researchers rarely saw the behaviour again, and wondered whether chimps still knew how to do it. So they set up an experiment, providing moss and leaves at the clay pit where the chimps had demonstrated the technique before.
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Then they watched to see whether chimpanzees would use leaves – a more common behaviour – or moss to soak up the mineral-rich water from the pit.
Most of the original moss-spongers used moss again during the experiment, and so did another 17 chimps, showing the practice had become more widespread. The researchers wondered what factors influenced which individuals adopted it: were they connected socially, or through families, for instance?
Keeping it in the family
This group of chimps has been observed for a long time, so the researchers were able to look through field data to calculate an index of how much time each chimpanzee spent with other individuals. It turned out that this metric wasn’t a good predictor of which chimps would use the moss sponge. Instead, moss-sponging was strongly correlated with having moss-sponging relatives.
The chimpanzees didn’t only learn from their parents: it was spread between any family members in either direction. “It’s like the family is the [crucible] where the behaviour is transmitted,” says Thibaud Gruber of the University of Geneva, Switzerland, one of the study authors.
But there were also individuals who learned the technique from non-family members. “Once a behaviour has been developed and spread to a few individuals, the majority of transmission will appear in the family, but if you hang out with some tool users, you’re still likely to develop a behaviour by social learning,” says Gruber.
“This is a wonderful contribution to the study of animal cultures,” says Andrew Whiten at the University of St Andrews, UK. “The accumulated evidence suggests that chimpanzees pass on scores of different traditions across Africa, but being able to see any of them originate and then spread is very much rarer.”
One of few previous studies to record new behaviours emerging and spreading in animal populations involved Japanese macaques on Koshima Island in the 1950s. A young female began washing sand off sweet potatoes in a river before eating them, and her peers soon did the same. Since then, the behaviour has spread from mother to offspring.
Imitation or invention
Moss-sponging seems to be following a similar pattern, says Frans de Waal of Emory University in Atlanta, Georgia.
“Social closeness is most of the time a bias in social learning, so that individuals learn the best from those they hang out with and whose behaviour interests them,” he says. We learn more readily from those we can identify with, and so do animals, he adds.
The origins of human culture may lie in the sharing of useful behaviours this way, says Whiten.
“What has been revealed in recent studies of cultural practices in all the great apes – chimpanzees, gorillas and orangutans – means it would be surprising if humans’ ape ancestors did not show similar behaviour, the foundations of the rich human cultures that have evolved in more recent times.”
However, some researchers think moss-sponging chimpanzees and potato-washing macaques aren’t learning by imitation at all, and each one invents the behaviour by itself.
“Chimpanzees fail to imitate in controlled experiments, and moss sponging does indeed occur in naive individuals,” says Claudio Tennie at the University of Tübingen, Germany. “Neither this nor the potato washing study – or indeed any other study – shows similar cultures in chimpanzees to our own.”
Gruber takes a different point of view. “Chimps are able, to a certain extent, to imitate, although it may not be as fine grained as in humans,” he says.
Journal reference: Science Advances, DOI: 10.1126/sciadv.1602750
Read more: Chimp social network shows how new ideas catch on; Well-travelled chimps more likely to pick up tools and innovate; Chimp filmed cleaning a corpse’s teeth in a mortuary-like ritual
Article amended on 27 April 2017
We corrected the number of chimps seen using the sponges,
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