Study: Great Apes Precisely Mirror Facial Expressions
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- University of Portsmouth research published in Scientific Reports found that great apes mirror facial expressions with surprising precision, drawing direct comparisons to the human Duchenne smile — a genuine smile engaging both mouth and eyes.
- The study analyzed 96 great apes — 39 orangutans and 57 chimpanzees living in eight separate groups, with subjects ranging across ages and genders.
- The findings suggest great apes 10–16 million years ago already matched the level of facial communication exactness seen in humans, an ability that likely conferred important social advantages.
- Apes were most likely to mirror each other's expressions when the upper teeth were not exposed, identified as a gentler expression, while chimpanzees actively avoided mimicking upper tooth rows to avoid signaling risky play, especially with older partners or males.
- Orangutans in longer play sessions showed greater precision in mirroring their playmate's expression, linking play duration to mimicry accuracy.
- Lead author Diane Austry said the animals "copy the exact same facial movement pattern their social partner uses, much like when a human mirrors another person's natural Duchenne smile," noting the pattern held for both automatic rapid responses and more delayed ones.
- Co-author Dr. Marina Davila Ross pointed to prior muscle-activity research showing chimpanzees and humans use the same muscles to produce laugh faces, calling the explicit replication "not previously known across the great apes."
Why it matters: By demonstrating that facial mimicry exactness isn't uniquely human but is shared across great ape species separated by 10–16 million years of evolution, the University of Portsmouth study gives researchers a measurable window into the evolutionary roots of emotional communication and challenges long-held assumptions about what separates primate social signaling from our own.
