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From seabirds to Arctic mammals, primates to great apes, certain species appear to kiss. Currently, scientists suggest that ancient hominins also engaged in this behavior – and might even have locked lips with early Homo sapiens.

Shared Microbial Evidence

It is not the first time experts have suggested Neanderthals and Homo sapiens were closely connected. Among earlier research, scientists have discovered modern people and their thick-browed cousins possessed the identical oral bacteria for hundreds of thousands of years after the two species split, suggesting they swapped saliva.

"Likely they were kissing," the researcher noted, explaining that the concept aligned with studies that has revealed humans of non-African ancestry contain Neanderthal DNA in their genetic makeup, revealing genetic mixing was at play.

Romantic Interpretation

"This offers a more romantic spin on ancient interactions," the lead researcher commented.

Writing in the journal a scientific periodical, the researcher and colleagues detail how, to investigate the evolutionary origins of kissing, they first had to come up with a description that was not limited to how people smooch.

Defining Intimate Contact

"Previously there were some efforts to define a intimate act, but it's largely focused on humans, which implies that essentially other animals don't kiss. Currently we understand that they likely engage, it might just not look from what our intimate contact resembles," explained the evolutionary biologist.

Nonetheless, she noted some behaviors that resembled kissing were something rather different – such as the chewing and food sharing, or "kiss-fighting", seen in aquatic species called French grunts.

As a result the team came up with a definition of kissing based on friendly interactions involving directed mouth-to-mouth contact with a member of the identical group, with some movement of the oral area but absence of nutrition.

Research Methods

Brindle explained they concentrated on accounts of intimate behavior in non-human species from Africa and Asia, including primates, apes and orangutans, and employed online videos to verify the observations.

Scientists then integrated this information with details on the genetic connections between extant and extinct types of such animals.

Evolutionary Timeline

The team propose the findings indicate kissing evolved approximately 21.5m and 16.9m years ago in the ancestors of the large apes.

Placement of ancient hominins on this evolutionary lineage suggests it is likely they, too, indulged in a kiss, the scientists conclude. But the activity may not have been limited to their specific group.

"Reality that modern people engage intimately, the reality that we currently have shown that ancient relatives very likely engaged, suggests that the two [species] are also likely to have engage," the researcher noted.

Evolutionary Significance

While the scientific reasoning is discussed, Brindle explained intimate contact could be employed in reproductive situations to potentially increase mating outcomes or help choose between partners, while it might help reinforce bonding when used in a non-sexual manner.

Another expert in the behavior of primates commented that as kissing behavior was seen in a broad spectrum of primates it made sense its origins extend far into our evolutionary past, and an analysis of different forms of intimate behavior among a broader range of species might push its beginnings back even earlier still.

"Behaviors that we consider as characteristics of our species, like intimate contact, are not exclusive to us if we look closely at other animals," he said.

Social Aspects

An archaeology expert explained that kissing had a cultural element as it was not common to all human groups.

"However, as people we thrive or fail on the quality of our emotional bonds, and ways of encouraging trust and intimacy will have been significant for millions of years," the professor stated. "It might be an concept that appears a bit incongruous to our misplaced ideas of a supposedly aggressive and aggressive past, but actually it should be expected that Neanderthals – and even Neanderthals and our human ancestors together – engaged intimately."