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From seabirds to Arctic mammals, chimpanzees to orangutans, various animals appear to kiss. Currently, scientists propose that ancient hominins did it too – and possibly locked lips with early Homo sapiens.

Common Oral Clues

It is not the first time experts have suggested ancient relatives and early modern humans were closely connected. Among previous studies, researchers have discovered humans and their thick-browed cousins shared the identical oral bacteria for millions of years after the two species split, implying they swapped saliva.

"Likely they were kissing," she said, explaining that the concept chimed with research that has found people of certain genetic backgrounds have bits of Neanderthal DNA in their genetic makeup, revealing genetic mixing was at play.

Intimate Spin

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

Publishing in the publication a scientific periodical, Brindle and colleagues report how, to explore the historical roots of kissing, they first had to come up with a description that was not limited to how people kiss.

Defining Kissing

"There have been some previous attempts to define a kiss, but it's very much been focused on humans, which implies that basically non-human species don't kiss. Now we know that they likely engage, it may appear different from what our intimate contact looks like," explained Brindle.

Nonetheless, she said some behaviors that resembled intimate contact were distinct activities – such as the chewing and transfer of food, or "kiss-fighting", seen in aquatic species called certain marine animals.

Consequently the research group developed a description of kissing based on social behaviors involving directed mouth-to-mouth contact with a member of the identical group, with some motion of the oral area but no transfer of nutrition.

Study Approach

Brindle explained they focused on accounts of kissing in primates from Africa and Asia, including bonobos, apes and great apes, and used online videos to confirm the reports.

The researchers then combined this information with details on the genetic connections between living and extinct types of such primates.

Historical Timeline

Researchers propose the findings indicate intimate contact evolved approximately 21.5 million and 16.9m years ago in the ancestors of the large apes.

The position of ancient hominins on this evolutionary lineage means it is probable they, too, indulged in a intimate act, the researchers say. But the behavior may not have been limited to their own species.

"The fact that humans engage intimately, the reality that we currently have demonstrated that Neanderthals very likely kissed, indicates that the both groups are also likely to have engage," Brindle added.

Biological Importance

While the evolutionary explanation is discussed, Brindle explained intimate contact could be used in reproductive situations to potentially enhance reproductive success or help choose between mates, while it could assist strengthen connections when used in a non-sexual manner.

A separate researcher in the activities of great apes commented that as intimate contact was observed in a broad spectrum of primates it made sense its origins lie deep in our ancient history, and an analysis of various types of intimate behavior among a wider variety of species might push its beginnings back even earlier still.

"Things that we consider as characteristics of human life, like intimate contact, are not unique to us if we look closely at different species," the expert noted.

Cultural Aspects

An archaeology expert explained that kissing had a social component as it was not universal to all societies.

"Nonetheless, as people we succeed or struggle on the strength of our relationships, and ways of promoting confidence and intimacy will have been significant for eons," she said. "It might be an image that seems a bit contradictory to our incorrect assumptions of a rather ruthless and ancient history, but actually it ought to be no surprise that ancient hominins – and including Neanderthals and our own species together – kissed."