The research also found that chimpanzees are able to produce these smile types silently, without being constrained by the accompanying laughing sound, ScienceDaily reported.
Lead researcher Marina Davila-Ross said…
Humans have the flexibility to show their smile with and without talking or laughing. This ability to flexibly use our facial expressions allows us to communicate in more explicit and versatile ways, but until now we didn’t know chimps could also flexibly produce facial expressions free from their vocalizations
The researchers filmed 46 chimpanzees at the Chimfunshi Wildlife Orphanage and used ChimpFACS –a facial action coding system adapted from the original research by Dr Paul Ekman – designed for chimpanzees– to measure their facial movements. FACS is used by EIA for forensic reports and research and features as a key module in the Behavioral Analysis and Investigative Interviewing module.
Co-author on the paper, Kim Bard, who designed ChimpFACS, said…
The coding system allows us to examine very subtle facial movements and compare human and chimpanzee facial expressions, based on their shared musculature.
The study investigated specific types of smiles that accompany laugh sounds and found that these smile types have the same evolutionary origin as human smiles when they are laughing. It suggests that these smile types of humans must have evolved from positive expressions of ancestral apes.
The study further suggests that flexibility in facial expressions was already present in ancestral apes and emerged long before humans evolved.