Some chimpanzees use sticks to fish for termites
Manoj Shah/Getty Images
Wild chimpanzees appear to learn skills from each other and then – much as humans do – improve on those techniques from one generation to the next.
In particular, young females that migrate between groups bring their cultural knowledge with them, and groups can combine new techniques with existing ones to get better at foraging for food. Such “cumulative culture” means some chimpanzee communities are becoming more technologically advanced over time – albeit very slowly, says Andrew Whiten at the University of St Andrews, UK.
“If chimpanzees have some cultural knowledge that the community they’re moving into doesn’t have, they may pass it on – just in the same way they’re passing the genes on,” he says. “And then that culture builds up from there.”
Scientists already knew that chimpanzees were capable of using tools in sophisticated ways and passing on that knowledge to their offspring. But in comparison with the rapid technological development of humans, it seemed that chimpanzees weren’t improving on previous innovations, says Whiten. The fact that chimpanzee tools are often made from biodegrading plants makes it difficult for scientists to track their cultural evolution.
Cassandra Gunasekaram at the University of Zurich in Switzerland suspected she might be able to apply genetic analysis to the puzzle. While male chimpanzees stay in their home area, young females leave their native communities to find mates elsewhere. She wondered if those females have brought their skill sets with them into their new groups.
To find out, she and her colleagues acquired data on 240 chimpanzees representing all four subspecies, which were previously collected by other research groups at 35 study sites in Africa. The data included precise information about what tools, if any, each of the animals used, and their genetic connections over the past 15,000 years. “The genetics give us a kind of time machine into the way culture has been transmitted across chimpanzees in the past,” says Whiten. “It’s quite a revelation that we can have these new insights.”
Some chimpanzees used complex combinations of tools, for example a drilling stick and a fishing brush fashioned by pulling a plant stem between their teeth, for hunting termites. The researchers found that the chimpanzees with the most advanced tool sets were three to five times more likely to share the same DNA than those that used simple tools or no tools at all, even though they might live thousands of kilometres away. And advanced tool use was also more strongly associated with female migration compared with simple or no tool use.
“Our interpretation is that these complex tool sets are really invented by perhaps building on a simpler form from before, and therefore they have to depend on transmission by females from the communities that invented them initially to all the other communities along the way,” says Whiten.
“It shows that complex tools would rely on social exchanges across groups – which is very surprising and exciting,” says Gunasekaram.
Thibaud Gruber at the University of Geneva isn’t surprised by the results, but says the definition of complex behaviour is debatable. “After working with chimps for 20 years, I would argue that stick use itself is complex,” he says.
His own team, for example, found what they called cumulative culture in chimpanzees that make sponges out of moss instead of leaves – which is no more complex, but works more efficiently to soak up mineral-rich water from clay pits. “It’s not a question of being more complex, but of just having a technique that builds on a previously established one,” he says.
Cumulative culture is still markedly slower in chimpanzees compared with humans, probably due to their different cognitive abilities and lack of speech, says Gunasekaram. Also, chimpanzees interact far less with others outside their communities compared with humans, giving them fewer opportunities to share culture.
Topics:
