Under a tree in Uganda’s Budongo forest in 2013, Catherine Hobaiter first mentioned the strange chimp behaviors she'd seen two years before. Hobaiter, a chimpanzee researcher at the University of St. Andrews in the UK, told fellow primatologist Thibaud Gruber that she had witnessed a group of chimps using a mix of moss and leaves to soak up drinking water from a watering hole in the forest. In 20 years of research, no one had observed this behavior in this community of chimps, and yet Hobaiter had managed to capture the behavior on video — numerous times.

"When she told me that she had all the videos on her laptop and, most importantly, that we could probably extract from these videos all the information necessary to document the spread of the behavior within the community," Gruber says in an email to The Verge, "I knew we were in business!"

"The chimpanzees just decided to display this novel behavior right in front of us."

Chimpanzees are widely considered the most "cultural" of all non-human animals, Gruber says. Their ability to use tools is well-known, and their capacity to transmit those behaviors socially has garnered a lot of attention in recent years. Until now, though, observations of chimps learning to use tools from each other had only taken place in captivity — a setting that, necessarily, doesn't resemble the wild. Captivity had limited the ecological validity of the earlier findings, says Gruber, who works at the University of Neuchâtel in Switzerland. "This has been a major point in the animal culture debate for the last 25 years," he explains, "with critics pointing out that there was no evidence so far that any of the presumed cultural behavior found in wild chimpanzees, were in fact socially learnt." As a result, some scientists think that "chimp culture" has nothing to do with the social transmission of culture in humans.

But that might soon change. Thanks to Hobaiter’s videos, researchers have been given a rare look at wild chimp society — one that, for the first time, shows the spread of a cultural behavior in the wild.

In the study, published today in PLOS Biology, Gruber and his team investigated how two new variations of "leaf-sponge" use spreads across a population. These single-use tools are usually the result of a chimp folding leaves into its mouth and subsequently using it to drink, or even to collect honey in experimental conditions. But Hobaiter’s footage showed that some chimps reuse their sponges, whereas others make them by mixing moss into the leaves. "The chimpanzees just decided to display this novel behavior right in front of us," Gruber says, "and we only needed our camcorders to capture the scenes."

With the footage in hand, the researchers gathered data and ran statistical models. The goal was to see if these novel behaviors were socially transmitted from chimp to chimp. And, according to their results, moss-sponging was a product of social learning among the chimp population. Leaf-sponge reuse, on the other hand, wasn't. What's more, every time an individual sees another chimpanzee perform a behavior, that first chimp is 15 times more likely to develop the behavior, the research showed. "Most interestingly," Gruber says, "the spread of the behavior was very fast, with seven individuals acquiring the novel behavior in only six days." This shows that chimpanzees can adopt new tools very quickly.

Critics think it's "just a bunch of anecdotes."

Due to the study’s observational nature, some researchers might object to the findings, Gruber says. "Many critics continue to think that what we collect in the field is a bunch of anecdotes, and like to claim that 'the plural of anecdotes’ isn’t data." But Gruber, who mostly focuses on experimental work, thinks that there’s value in collecting observational data in the field. It’s "highly frustrating" when people universally suggest otherwise, he says, even if you’ve collected "over 1,000 instances of the same behavior."

Still, some researchers have embraced the results. Shinya Yamamoto, a primatologist at Kobe University in Japan, told The Verge that the study’s results provide sound evidence of tool-use transmission. "We are now almost sure that chimpanzees have socially transmitted culture," he says. Yamamoto’s own work also focused on social learning and tool-use in chimps, but his experiments took place in a lab. "This is the start point of further investigation of what are similar and different between human and chimpanzee cultures — to know the basis of technology would be helpful to know the future of our technological societies."

human ancestors likely learned cultural behaviors from each other

Along those lines, Gruber thinks the findings strongly support the idea that the last common ancestors of chimps and humans could have learned cultural behaviors from each other. Moreover, chimps appear to build upon old knowledge "little by little," Gruber says, so it’s also likely that "little changes in cultural knowledge — in contrast to big qualitative jumps — characterized early hominin species." But before he can dive further into the possible implications for human evolution, researchers will have to address the specific mechanisms that allow for the transmission of chimpanzee culture. "Unless we do that, there will always be questions about whether the two phenomena are really comparable."

Unfortunately, figuring out just how "chimp culture" works will take time — time that chimpanzees might not have. Like many forests in Africa, the Budongo Forest is under constant threat from deforestation. So "it is great to have finally this evidence of social learning in wild chimpanzees, but it will be to no use if chimpanzees disappear in the wild in the next 50 years," Gruber says. That’s why "it’s of utmost importance to conserve chimpanzees, for themselves, for their cultural knowledge, and for all the still unknown information that they can give us about our past."