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From seabirds to Arctic mammals, primates to orangutans, certain species appear to kiss. Currently, scientists suggest that Neanderthals also engaged in this behavior – and might even have locked lips with modern humans.

Shared Oral Clues

It is not the first time experts have suggested ancient relatives and early modern humans were intimately acquainted. In earlier research, researchers have discovered humans and their thick-browed cousins possessed the same mouth microbe for millions of years after the evolutionary divergence, implying they swapped saliva.

"Likely they were engaging in intimate contact," she said, explaining that the concept chimed with studies that has revealed humans of non-African ancestry have bits of ancient genetic material in their genetic makeup, revealing genetic mixing was occurring.

Romantic Spin

"This offers a more romantic perspective on human-Neanderthal relations," the lead researcher said.

Writing in the journal a scientific periodical, Brindle and her team detail how, to explore the historical roots of kissing, they first had to develop a description that was not restricted by how people kiss.

Defining Intimate Contact

"Previously there were some efforts to describe a kiss, but it's very much been focused on humans, which means that essentially other animals do not engage in this. Currently we understand that they likely engage, it might just not look from what human kissing looks like," explained Brindle.

However, she said some actions that resembled kissing were something rather different – such as the chewing and food sharing, or "kiss-fighting", observed in fish known as certain marine animals.

Consequently the research group developed a description of kissing centered around social behaviors involving directed oral interaction with a member of the same species, with some motion of the mouth but no transfer of nutrition.

Research Methods

Brindle explained they focused on reports of intimate behavior in non-human species from Africa and Asian regions, including bonobos, apes and great apes, and employed online videos to verify the observations.

Scientists then combined this information with details on the genetic connections between extant and ancient species of such primates.

Historical Origins

The team propose the results suggest kissing evolved somewhere between 21.5 million and 16.9 million years ago in the predecessors of the great primates.

Placement of Neanderthals on this evolutionary lineage means it is probable they, too, engaged in a intimate act, the researchers conclude. But the activity may not have been confined to their specific group.

"The fact that humans kiss, the reality that we currently have shown that Neanderthals very likely engaged, indicates that the both groups are probably did engage," the researcher added.

Evolutionary Significance

Although the evolutionary explanation is debated, Brindle explained kissing could be employed in reproductive situations to possibly increase mating outcomes or help choose between mates, while it could assist strengthen connections when practiced in a non-sexual manner.

A separate researcher in the behavior of great apes said that as intimate contact was seen in a broad spectrum of primates it made sense its origins lie deep in our ancient history, and an examination of different forms of kissing among a broader range of species might extend its beginnings back even earlier still.

"Things that we think of as signatures of human life, like kissing, are not unique to us if we look closely at different species," he said.

Cultural Aspects

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

"Nonetheless, as humans we succeed or struggle on the quality of our relationships, and methods of encouraging trust and intimacy will have been significant for eons," the professor stated. "It might be an image that appears a bit incongruous to our misplaced ideas of a rather ruthless and aggressive past, but really it ought to be expected that ancient hominins – and including Neanderthals and our own species collectively – kissed."