It may not be the most romantic thing to say, but kissing accomplishes very little from a biological standpoint. If anything, a smooch’s ability to facilitate the spread of communicable diseases can do more harm than good. But according to a review of humanity’s evolutionary journey, there was a time when kisses potentially signified a more hygienic—and hairier—ape.
Adriano Lameira, a primatologist and evolutionary psychologist at the University of Warwick, recently conducted a comprehensive examination of existing hypotheses behind kissing’s potential origins, such as nursing infants and pre-chewing food for young apes. And while Lameira’s conclusion also offers far more utilitarian beginnings than today’s sign of love, he theorizes kissing may come from adults cleaning each other.
“[K]issing isn’t a derived signal of affection in humans, it instead represents a surviving devolved… form of primate grooming that conserved its ancestral form, context, and function,” Lameira argued in a paper published in the journal, Evolutionary Anthropology.
Today’s primates usually finish grooming sessions by protruding their lips and carefully sucking excess debris, insects, and parasites caught in another ape’s fur. According to Lameira, this moment marks the conclusion of an often “time- and labor-intensive ritual” that forges and reinforces social bonds. But cleaning sessions are only long and focused as an ape’s body hair allows.
[Related: Ancient Mesopotamian texts show when and why humans first kissed.]
Grooming logically took less time and effort as human ancestors gradually evolved less fur over thousands of years, but Lameria argues these rudimentary kisses remained social staples despite being less of a health necessity. He theorizes these subsequently “shorter sessions would have predictably retained a final ‘kissing’ stage,” until it eventually became the “only vestige of a once ritualistic behavior for signaling and strengthening social and kinship ties in an ancestral ape.”
As Phys.org explained on October 26th, however, it’s important to note that kissing isn’t universal across human cultures. A 2015 study in the journal American Anthropologist cites that just 46-percent of 168 surveyed cultures around the world maintain romantic and social kissing practices, while indigenous hunter-gatherer communities even view kisses as somewhat gross. Not only that, but many non-ape primates engage in different social bonding rituals. The capuchin monkey, for example, sticks their fingers in the nostrils and eyes of their closest community members.
Lameira, however, takes time to note such exceptions in their paper. He also cites how grooming behaviors traditionally appear in terrestrial-based apes more prone to parasites than their tree-dwelling relatives such as capuchins, potentially further supporting his theory. Either way, Lameira expressed hope in his conclusion that the “final kiss hypothesis” will inspire further research and today’s great ape grooming behaviors, especially those with varying amounts of fur.
“For future evolutionary insight into the evolution of human kissing, and other behaviors uniquely exhibited by our species, it will be important to retain in mind and ponder the influence of the broader socio-ecological, cognitive, and communicative context of human ancestors,” he wrote.
