If you’ve noticed the darkening facial expression of your friend as you describe something terrible that happened, you’re witnessing emotional mimicry. Sometimes without even realizing it, we display empathy by mirroring the expressions of others. Non-human primates, such as rhesus macaques, also have been shown to mirror human expressions, in what’s perhaps a show of cross-species empathy. Now, a new study in PLOS One shows that the emotional mimicry between primates goes both ways.
Psychologists from Germany, Italy, and the United Kingdom experimented to determine whether humans would naturally mirror the facial expressions of other primates. A sample of 212 study participants who had no expert experience with other primates watched videos of monkeys and apes making various faces—from threat displays to play faces to neutral expressions. Next, each participant was asked to categorize the primate facial expressions they’d seen as representing positive or negative emotions and rank them relative to happiness, anger, sadness, fear, disgust, and surprise.
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The results showed that humans are surprisingly good at diagnosing the facial expressions of non-human primates. The study participants also were adept at associating the faces with emotional labels, like “angry” or “happy,” even though both of those emotions in other primates may include open-mouth displays of the teeth.
“The research suggests that humans are capable of perceiving and resonating with the emotional states of non-human animals,” said the study authors in a press release.
Furthermore, videos of the participants’ own faces as they watched other primate expressions revealed significant emotional mimicry. When the monkey or ape made a negative face, participants tended to make a negative face too, and the converse for happy facial expressions. The strength of the human’s mimicry of other primates depended on how close they felt to each primate—in particular, they felt closer to primates making positive facial expressions.
“By demonstrating the emotional and communicative bridges that connect humans with other animals, we challenge the long-standing divide between species,” explained lead author and Humboldt University in Berlin psychologist Ursula Hess, “and invite a shift in perspective—one that places all living beings at the center of moral consideration.”
So the next time you see another species of primate, be sure to flash it your best friendly smile. 
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Lead image: Patrick Rolands / Shutterstock
