Kissing has been a well-established behaviour throughout human history. It is a symbol of affection and intimacy. But why do we kiss? Why do humans protrude their lips with slight suction, while capuchin monkeys opt for a more…unique approach, poking their fingers into their friends’ eyes and nostrils? New research delves into the origins of this intriguing behaviour.
Many theories have been proposed to explain the human practice of kissing. One suggests it evolved from nurturing behaviors like premastication, where caregivers fed infants pre-chewed food. Another suggests that kissing might have served as a compatibility test, allowing mates to assess each other’s health. However, a new theory proposes that kissing originated as the final step in a grooming ritual, designed to remove parasites and debris.
Great apes engage in grooming as a social behaviour, to strengthen bonds and remove parasites. While mouth-to-mouth contact is rare among great apes, typically occurring only after conflict, some species exhibit “kissing” as a final stage of grooming. In this stage, the groomer uses their lips to suck on the fur or skin of their partner to remove debris or parasites.
The theory suggests that humans may have once engaged in similar grooming practices. As we lost our fur, the hygienic necessity of grooming decreased. However, the final “kissing” stage persisted, evolving into a symbolic gesture to signal and strengthen social bonds. Once again, great apes have shed fascinating insight into our own evolutionary history.
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