Gorillas use human-life facial expressions to communicate with each other, however the Western Lowland gorilla equivalent of a grin means something completely different, as psychologists from the University of Portsmouth recently discovered.
Psychologists from the University of Portsmouth have published a paper suggesting gorillas use human-like facial expressions to communicate moods with one another. Not only that, but two of the expressions, both of which resemble grinning, could show the origins of the human smile.
The findings were published in the American Journal of Primatology and the observed gorillas used a variety of different expressions. Their play face, featuring an open mouth and showing no teeth, shows a playful mood, and it’s usually accompanied by physical contact. An open-mouthed face, displaying the top teeth, could be a submissive smile, as it mixes both the play face and the bared-teeth expression, showing appeasement.
Subtle differences in facial expression and vocalization could mean very different things. Some primate species display the bared-teeth expression, which is similar to the human smile, but it is used only by subordinates. These species have very different social organizations than humans.
This does partly explain why some people have a nervous or fake grin to hide their own feelings. Observant people tend to remark that the smiles don’t include a twinkling of the eyes.