Findings of a new study have revealed that, just like humans, chimpanzees are able to smile without producing a laughing sound.
Marina Davila-Ross, from the University of Portsmouth, and colleagues who conducted the study have found that chimps can produce facial expressions as a means of communicating their emotions.
For the new study published in the journal PLOS ONE on Wednesday, the researchers videotaped 46 chimpanzees living in the Chimfunshi Wildlife Orphanage in Zambia.
Half of the animals were born in the wild but were rescued and brought to the sanctuary as orphans. The other half of these chimps, on the other hand, were bred in the sanctuary.
Using a program called ChimpFACS, a scientific tool designed to record and analyze the facial movements of primates, the researchers were able to examine the subtle facial movements of the animals.
The researchers then compared the facial expressions of humans and chimpanzees. They found that chimps make the same types of "laugh faces" when there were laugh sounds as when there were none.
The researchers said that humans can smile without laughing or talking, which allows better communication, but the new study reveals that chimps can also produce these facial expressions without vocalizations.
"Humans have the flexibility to show their smile with and without talking or laughing," Davila-Ross said. "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."
By looking into particular types of smiles, the researchers also found that the smile types of chimpanzees have the same evolutionary origin as the smiles that humans produce when they laugh, which suggests that these types of smiles in humans have likely evolved from ancestral apes.
"During laughter, the chimpanzees frequently showed three distinctive facial muscle activations that characterize human laugh faces," the researchers wrote. "The ChimpFACS data, thus, support the claim of fewest possible evolutionary changes, where laugh faces of humans must have gradually emerged in morph from open-mouth faces of ancestral apes not from silent-bared teeth displays of ancestral apes."
The researchers likewise found that there were different uses for facial expression and vocalization, as well as facial expression alone, in social play, such as when the primates are in physical contact with their playmates or when they match their playmates' open-mouthed faces.
Photo: Rod Waddington | Flickr
