A new study indicates that kissing likely originated in ancestral apes between 21.5 million and 16.9 million years ago. Researchers analyzed primate behaviors and found an 84 percent chance that Neanderthals also engaged in the practice. The findings challenge the idea that romantic kissing is a recent cultural invention.
Researchers led by Matilda Brindle at the University of Oxford have traced the evolutionary origins of kissing, suggesting it emerged in early apes millions of years ago. By reviewing scientific literature and consulting primate experts, the team defined kissing as non-antagonistic mouth-to-mouth contact involving lip movement, excluding food transfer or kisses on other body parts. This definition helped identify instances in modern primates like chimpanzees, bonobos, and orangutans.
Using Bayesian modeling on a primate family tree, the study simulated evolutionary scenarios and concluded that kissing probably evolved between 21.5 million and 16.9 million years ago. "Kissing seems a bit of an evolutionary paradox," Brindle says. "It probably doesn’t aid survival and could even be risky in terms of helping pathogen transmission."
The research also points to an 84 percent likelihood that Neanderthals kissed, supported by evidence of shared oral bacteria with Homo sapiens and Neanderthal DNA in non-African humans. "Obviously, that’s just Neanderthals kissing; we don’t know who they’re kissing," Brindle notes. "But together with the evidence that humans and Neanderthals had a similar oral microbiome... we would argue they were probably kissing each other."
Historical records show sexual kissing in ancient Mesopotamia and Egypt at least 4,500 years ago, but it appears in only 46 percent of human cultures, fueling debates on its origins. Brindle proposes two hypotheses: sexual kissing may assess mate quality, such as detecting bad breath, or promote arousal for reproductive success; alternatively, it could stem from grooming to strengthen bonds and reduce social tension, as seen in chimpanzees "kissing and making up" after fights.
Zanna Clay at Durham University agrees on its affiliative role in primates but questions the sexual aspect. "I think our results show very clearly that kissing has evolved," Brindle asserts. Troels Pank Arbøll from the University of Copenhagen, who studied ancient Mesopotamian texts, says the work provides a stronger basis for kissing's long human history, though cultural influences likely play a role in its varying prevalence.