New research suggests that humanity's most intimate gesture evolved from a surprising source: our ancestors' need to groom one another.
A study published this month reveals kissing likely began as a grooming behavior in early humans, not as a sign of affection. University of Warwick psychologist Adriano R. Lameira found that our ancestors used protruded lips to clean each other's fur and skin.
According to Lameira, evidence suggests kissing originated as a grooming technique used by early primates to remove parasites and debris from each other's fur. The behavior involved using protruded lips to suck on the skin or fur of another individual.
"Kissing is likely the conserved final mouth-contact stage of a grooming bout when the groomer sucks with protruded lips the fur or skin of the groomed to latch onto debris or a parasite," Lameira said.
As humans evolved to have less body hair over millions of years, this grooming behavior became less necessary for hygiene. However, the mouth-to-mouth contact persisted and eventually developed into what we now recognize as kissing.
Lameira estimates humans became a "kissing ape" species approximately 2 million to 4 million years ago. The earliest known record of human kissing appears in Mesopotamian texts from around 2500 B.C.
The researcher noted that how kissing transitioned into a sexual or romantic act remains unclear and requires further study. He explained that kissing with "sexual intent" represents a special case of the behavior that developed later.
"Only once kissing was used as a general convention for showing affection could kissing become a mutual mouth-to-mouth act," Lameira said.
Today, kissing serves as a "crystallized symbol of trust and affiliation" in human society, according to the study. Lameira emphasized that few natural human behaviors carry the same symbolic weight and social significance as kissing in modern culture.
The research challenges common assumptions about the inherently romantic nature of kissing. It suggests that this ubiquitous human behavior may have mundane evolutionary origins rooted in practical grooming rather than expressions of love or attraction.