But just when many scientists have come to accept the existence of animal cultures, many of those cultures might vanish. Kalan and her colleagues have shown, through years of intensive fieldwork, that the very presence of humans has eroded the diversity of chimpanzee behavior. Where we flourish, their cultures shrivel. It is a bitterly ironic thing to learn on the 20th anniversary of Whiten’s classic study.
“It’s amazing to think that just 60 years ago, we knew next to nothing of the behavior of our sister species in the wild,” Whiten says. “But now, just as we are truly getting to know our primate cousins, the actions of humans are closing the window on all we have discovered.”
Read: Can humans understand chimps?
“Sometimes in the rush to conserve the species, I think we forget about the individuals,” says Cat Hobaiter, a primatologist at the University of St. Andrews. “Each population, each community, even each generation of chimpanzees is unique. An event might only have a small impact on the total population of chimpanzees, but it may wipe out an entire community—an entire culture. No matter what we do to restore habitat or support population growth, we may never be able to restore that culture.”
Since 2010, Kalan has been working on the Pan African Programme, an intensive effort to catalog chimp behavior in 46 sites across the species’ entire range, led by Hjalmar Kühl, Christophe Boesch, and Mimi Arandjelovic. At each site, the team checked whether chimps were carrying out any of 31 different behaviors, including many from Whiten’s original list, and some that had only been recently discovered. “We had things like termite fishing, ant fishing, algae fishing, stone throwing, leaf clipping, using sticks as marrow picks, using caves, bathing, and nut cracking,” Kalan says.
After all this work, the team showed that chimps living in areas most affected by humans were 88 percent less likely to show any one of the 31 behaviors than those living in the most unaffected regions. “However we divided up the data, we got the same very obvious pattern,” Kalan says.
It’s hard to prove a negative, though, and it’s always possible that the chimps were up to their old tricks without the team noticing. But the Pan African Programme team filmed the apes using camera traps, to capture behavior without disturbing the animals. It checked for certain traditions by looking for discarded tools, or checking for specific foods among the apes’ poop. And it scored the chimps generously: Even if it only saw a particular behavior once, it recorded the behavior as being present. If anything, the new results underestimate the extent to which humans suppress chimpanzee cultures.
Such suppression isn’t deliberate. Chimpanzees and other apes learn skills and customs from one another, and those chains of tradition depend on having enough individuals to learn from. So when humans kill chimps for bushmeat, they aren’t just killing individuals—they are also destroying opportunities for the survivors to learn new things. When they fragment the forests in which chimps live, they’re stopping the flow of ideas between populations.