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.
However, the findings published in the American Journal of Primatology show their smiles mean different things. The Portsmouth researchers found these expressions, observed in Western Lowland gorillas, expressed a number of emotions.
One, a “play face”, featuring an open mouth and showing no teeth, denotes a playful mood, usually accompanied with physical contact. Another, which is open-mouthed and displaying top teeth, could be a submissive smile — as it mixes the play face and a bared-teeth expression, which indicates appeasement. “Many primate species also show their teeth when they scream,”
Bridget Waller, the lead researcher told Wired.co.uk in an email. “These expressions tend to look different to the expressions I studied in gorillas, as the upper and lower teeth are both exposed, and the mouth widely open. The expression is more tense, and accompanied by very different vocalisations. The vocalised element of the scream can differ depending on whether the screamer is an aggressor or a victim.”
In short: subtle differences in facial expression and vocals mean quite different things in primate posturing — one is obedient and appeasing, the other screaming and aggressive. But does this mean that our own smile is inherently passive and submissive? “In some primate species the bared-teeth display (the expression similar to the human smile) is used only by subordinates, but these species have a very different social organisation to humans,” says Waller. “They tend to have very strict dominance hierarchies, whereas we have a more relaxed social structure. So, in some circumstances humans might use smiling as a subordinate signal, but is can also be used as a genuine signal of friendliness.”
