In social interactions, our faces can become like mirrors, reflecting subtle expressions back at our conversation partner. It might be for validation, or sympathy, but whatever the purpose, facial mimicry is a key part of humanity’s complex social world. We aren’t alone among animals in the use of facial communication, but our degree of finesse and precision had only been seen in our relatives, gorillas. Now, researchers have recently uncovered this social superpower in another species, one very different from hypersocial apes—the sun bear.
Sun bears (Helarctos malayanus) are the world’s smallest bears, Rottweiler-sized animals found in Southeast Asian rainforests. Unlike primates, which tend to show the most frequent and sophisticated use of facial expressions, sun bears don’t form large, hierarchical groups in which complex facial expressions would seem to play an important role in communication. They’re not exactly antisocial, but sun bears mostly opt to go their own ways, says Marina Davila-Ross, a comparative psychologist at the University of Portsmouth and senior author on the study, which published today in the journal Scientific Reports.
“As wild individuals, they are living more or less by themselves,” says Davila-Ross. “The males are quite territorial and the females are with their offspring, so it's as close to a solitary species as it can get.”
It’s this solitary nature that makes the discovery of sun bears’ facial mimicry prowess so unexpected. The findings suggest that sophisticated social skills like facial mimicry aren’t limited to species that are inherently social. If even mammals that evolved for a life of relative solitude can interact this way, then facial mimicry may not be an elite, social trait at all. Perhaps complex social interactions are more widespread among mammals than we thought.
Mimes in the Forest
Davila-Ross was studying orangutans at a wildlife rehabilitation center in Sabah, Malaysia, on the island of Borneo, when she became intrigued by the bears at the nearby Bornean Sun Bear Conservation Centre, a rescue and rehabilitation organization. After watching the bears play with each other, she noticed something curious about their interactions: They seemed to be mimicking each other’s facial expressions. Realizing that very little was known about sun bear behavior, Davila-Ross and her colleagues decided to investigate further.
She and her team observed 22 sun bears in their forested enclosures, recording more than 370 different play bouts on video. The researches then pored over the footage, meticulously evaluating and tallying differences in the bears’ facial expressions and their timing.
The bears would often open their mouths towards their play partner in one of two ways, either with the teeth exposed or hidden under the lips. The researchers found that the bears were predominantly producing either of these open-mouth expressions when they saw their play partner was looking at them. Changing a facial expression when given attention by someone else, until now, was only known in primates and dogs—the latter of which shares a life with, and has been domesticated by, humans.
When met with an open-mouthed signal, most of the bears would copy the expression right back, often within one second of seeing the expression. This “rapid facial mimicry,” also had only been seen in primates and dogs.
Most interestingly, the copycats reproduced an exact match of their partner’s chosen face, not just throwing out any old open-mouthed mug. This precise expression matching was thought to be the domain of humans and gorillas only, so bears trying it out is completely new.
Apes and dogs are social butterflies compared to sun bears, so the bears possessing such complex facial communication skills is unexpected. Evolutionarily speaking, the bears aren’t closely related to dogs, and far less so to apes, so it’s not even a relic of kinship. This finding raises the possibility that sun bears—and other solitary species—can interact with each other in more complex ways than we thought.
Setting May Be Everything
Davila-Ross doesn’t think she and her colleagues were just lucky to have found the one, oddball, non-primate outlier that can copy faces. Rather, she thinks the results show that we may need to rethink what is possible across all mammals.
“It seems likely that other species also have these abilities,” says Davila-Ross, even the more solitary species.
For Elisabetta Palagi, an ethologist at the University of Pisa in Italy not involved in this study, the research provides an important illustration of social potential across the entire mammal family tree.
“I think it's a good paper,” Palagi says, but she notes that it’s important to consider that the bears’ environmental setting at the Centre doesn’t match their wild, solo state.
“These are rehabilitated animals, so they were forced to live together,” Palagi says. Such an opportunity to become familiar with one another might make it easier to adopt new social cues. Orangutans, for example aren’t particularly social in the wild, she says, but they make connections and alliances once in group settings in captivity.
Palagi is curious if the degree of facial mimicry differs between bears with more or less familiarity with their play partner. She also thinks it’s interesting that the mirroring doesn’t influence the length of the play session, like it does in dogs. They signal to each other a “synchrony” of playful moods, letting the playing go on longer. So what is the facial mimicry in sun bears even for?
It’s an avenue of research that Davila-Ross says needs more investigation, noting that we know little about facial communication in general across all species. In the future, Davila-Ross hopes to look into how personality differences between bears may influence the success of releasing rehabilitated animals back into the forest.
She hopes other groups will look into facial expressions in other, non-social mammals to see just how widespread this mimicry skill set may be. There may be a lot more going on behind the eyes of our more distant, fuzzy cousins than we assumed.