Whether it’s a college student playing a roommate their favorite song or a child showing their parent a dirty rock they found on the ground (“Not again!”), humans love sharing things we find fascinating just for the sake of it. The desire to sit your loved ones down and force them to watch your favorite movie has long been thought to be distinctly human— an inclination not shared by our primate relatives.
Still, that might not keep an animal behavior researcher from wondering from time to time whether an activity considered unique to humans might turn up in some form in chimps, orangutans, bonobos or gorillas.
A chance observation in Uganda’s Kibale National Park provides a small hint that such a possible behavior exists—and that further research on chimps sharing just for the hell of it might well be worth pursuing.
The ability to “share” attention is thought to be a pivotal development in human evolution, serving as a needed precursor to more complex cooperative behaviors. Babies as young as 10 months hold out items for their caretakers to see, with seemingly no other purpose beyond letting mom, dad or big sister in on something they find cool or interesting. “Being really motivated to do this a lot, from a very early age, is absolutely critical to us engaging in joint action together,” says Katie Slocombe, a comparative psychologist at the University of York in England and senior author of the study.
It’s not that chimps don’t ever share attention. They have been known to direct the attention of a companion or a human caretaker to communicate what they want. A chimp might point to a specific spot on its body where it desires to be groomed or gesture to a favorite toy it wants to play with.
But Slocombe and her team were astonished in the midafternoon on May 18, 2019, when they were studying the Ngogo chimp community in Kibale and saw something remarkable. An adult female named Fiona was fiddling with a leaf while her infant was in her lap and her mother, Sutherland, was by her side. Fiona then held out the leaf in front of Sutherland’s face, making tiny readjustments to be sure it was directly in her gaze, until she looked down at it. Fiona only resumed fiddling with the leaf when she was satisfied that her mother noticed what she was doing. Slocombe, who has worked with chimps for close to two decades, was blown away. “I’ve never seen them do anything like that,” she says.
This all happened just once and has not yet been seen again—either with Fiona or the other chimps that Slocombe follows. But that one instance was enough to add an exciting twist to Slocombe’s research. Confirming that Fiona’s goal was just for her mom to pay attention to something and nothing more is tricky to ascertain, especially with only one observation. The team was particularly interested in whether Fiona’s action could be part of a mysterious behavior known as “leaf grooming.”
The exact function of leaf grooming, in which a chimp fiddles with and closely inspects a leaf, isn’t clear, but the apes tend to do it after they’ve been grooming themselves or another chimp. Slocombe says that the chimps might be trying to point out parasites they find on the leaves during grooming to get a better look at them or that the behavior may just be a way to relieve anxiety, a simian version of a fidget spinner.
The team combed through video footage to look for other instances of leaf grooming behavior that resembled what Fiona was doing before she showed the leaf to her mom. Looking back at 84 previous observations of leaf grooming performed by 37 different chimps from Ngogo and the nearby community of Kanyawara, the researchers saw no evidence that the behavior tended to lead to play or more grooming, so Fiona likely wasn’t trying to initiate either activity by holding out a leaf. Food sharing is also an unlikely explanation because the chimps never ate anything off the leaves they groomed or ate the leaves themselves. This makes the researchers confident that Fiona had no ulterior motive other than to stick her leaf in Sutherland’s face—she just wanted to share something neat with her mom. Slocombe and her colleagues published their research on November 14 in Proceedings of the National Academy of Sciences USA.
Others are a bit more skeptical that Fiona truly had no other intention but to share the experience of leaf contemplation with her family. “It does look like the daughter is showing something to her mother,” says Garriy Shteynberg, a psychologist at the University of Tennessee, Knoxville, who was not involved with the study. “It is heartening for me to see this.” He adds that he “can’t tell whether this is instrumental sharing or sharing for sharing’s sake,” however. Shteynberg also notes that Fiona and Sutherland don’t exchange a “knowing look” like humans do when sharing attention and feels the chimps may be demonstrating a rudimentary version of a much more complex behavior in humans. “It would be surprising that our closest relatives wouldn’t have some inkling of this kind of sociality,” he says.
Michael Tomasello, a psychologist at Duke University, who was also not involved in the study, agrees that more evidence is needed to support the claim. “I would be much more convinced if it was either a large body of observations under reasonably controlled circumstances or even an experiment,” he says.
Slocombe welcomes the skepticism. “I think that’s very healthy in science,” she says. She is also hopeful that her team’s finding will prompt other chimpanzee researchers to look more closely for similar behaviors in their own subjects to see if the result holds up. And she thinks it would be worthwhile to see if nonprimates, such as dogs, ever just want you to check out something cool, too. “Generally … most dogs bring you things because they want you to do something with [it],” she says. “But maybe not always.”
