Why Do We Smooch? There's a 'Final Kiss Hypothesis'

It is, quite possibly, the least romantic definition of a kiss in the annals of history, one that describes the kisser kissing the kissee "with protruding lips and sucking action to latch on and remove a parasite or debris." But that description in Evolutionary Anthropology may go a long way in explaining why humans smooch, reports Phys.org. The study out of the UK's University of Warwick traces the evolutionary origin of human kissing back to great apes—and more specifically to their grooming habits. The apes pluck parasites off each other with their hands and mouth, and the practice is important not only in terms of hygiene but in establishing and maintaining social bonds, says lead researcher Adriano R. Lameira.

The very last part of the grooming practice refers to the aforementioned habit of using the lips to clear a bug or a bit of debris. Because this "resembles the form, context, and function of human kissing today," researchers have dubbed this the "groomer's final kiss hypothesis," per Interesting Engineering. Humans evolved to have less hair, reducing the need for this type of hygienic grooming. But the "kissing" practice stuck around and evolved because it helped with social bonding, according to the hypothesis. "What was once a time- and labor-intensive ritual to cement and strengthen close social ties became gradually compressed until a groomer's final kiss turned into a crystalized symbol of trust and affiliation," reads the study. (More kissing stories.)