Grooming in Apes Led to Kissing in Humans

Kissing has been a popular practice in human society for an eternity. But its evolutionary roots are somewhat of a mystery, given the fact that it is a pleasant activity that would seem to offer no survival-related advantages—at least none that are obvious.

But in an article recently published in the journal Evolutionary Anthropology, University of Warwick primatologist and evolutionary psychologist Adriano Lameira introduces an intriguing theory that links kissing to ancient primate behavior, creating a scenario where evolution could have gradually brought the practice into being.

Grooming Felt Good, but Kissing Felt Even Better

According to Lameira, the primate behavior that laid the groundwork for the “invention” of kissing was grooming, which has been observed in different primate species and presumably was also common among ancient hominins (human ancestors).

Grooming involves the removal of parasites, debris, and dead skin from the body by picking with the fingers or, in some cases, by sucking with the mouth and lips. The latter behavior normally would occur at the last stage of the process, when a primate grooming another primate might need to suck out whatever the fingers were not nimble enough to remove from the hair or fur of their primate partner or buddy.

Snow monkey grooming another snow monkey in pool. (Trey Ratcliff/CC BY-NC-SA 2.0)

As time passed and some hominin species lost body hair (evolution working its magic), grooming would have become less common. Grooming regimens likely would have become shorter and less complicated as well, until most of these behaviors would have been abandoned—except for that final touch, the sucking with the lips and mouth at the end, which eventually evolved into a mouth-to-mouth phenomena.

“The hygienic relevance of grooming decreased over human evolution due to fur-loss,” Lameira wrote in his paper, “but shorter sessions would have predictably retained a final ‘kissing’ stage, ultimately, remaining the only vestige of a once ritualistic behavior for signaling and strengthening social and kinship ties in an ancestral ape.”

In other words, for even the most hairless primate species, that activity was just too satisfying to give up.

There is inevitably a high degree of speculation involved in this theory, which is unavoidable when the subject involves the evolution of behavior in ancient hominin species. At this point researchers can only trace kissing in humans back as far as 4,500 years ago in Mesopotamia, where it was displayed in artwork. Beyond that, there is real uncertainty about the history of this fun and seemingly rather unusual practice.

Nevertheless, it is interesting to note that two other currently-living primates who display animal versions of kissing behavior are chimpanzees and bonobos. These are the two primate species that are most closely related to humans, which may offer some support for Dr. Lameira’s evolutionary theory about how kissing came to be.

So why would grooming have persisted long enough through time in primates and hominins to evolve into the Homo sapiens lip hug?

“Grooming helps to establish and maintain alliances, hierarchies, and group cohesion through social touch, with the consequent release of endorphins, which reduces stress and promotes feelings of well-being between groomer and groomed, further cementing social ties,” Dr. Lameira wrote, explaining why grooming is good for a primate’s health, and presumably would enhance long-term survival odds as a result.

Everyone Loves to Kiss … or Do They?

In Adriano Lameira’s theory that kissing in essence represents an extremely simplified and somewhat abstracted form of grooming does link the practice to actual behavior observed in nature. And his narrative about how more complex grooming practices in ancient times devolved into simple lip-locking in modern humans seems logical and plausible.

Adult Barbary Ape kissing baby monkey. (Public Domain).

It must be noted, however, that the whole observed range of kissing behavior, from polite pecking to passionate smooching, isn’t as popular as one might think given its ubiquity in the culture we inhabit.

A 2015 study that appeared in the journal American Anthropologist reported that only 46% of 168 cultures surveyed embraced romantic and/or social kissing practices. This raises the possibility that kissing is not as deeply rooted in evolutionary forces as might be expected.

It is possible that ancient humans (or other primates, for that matter) only discovered the pleasures of kissing by accident, or through some fun experimentation, which didn’t necessarily take place everywhere. This could be why the planet is split nearly 50-50 between smooching and non-smooching cultures.

For his part, Dr. Lameira recognizes that his theory doesn’t explain every aspect of the history of kissing, and that other uniquely human factors are undoubtedly involved.

“For future evolutionary insight into the evolution of human kissing, and other behaviors uniquely exhibited by our species,” he wrote, “it will be important to retain in mind and ponder the influence of the broader socioecological, cognitive, and communicative context of human ancestors.”

Top image: Cary Grant kissing Eva Marie Saint in the movie ‘North by Northwest.’

Source: Public Domain.

By Nathan Falde