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From seabirds to polar bears, chimpanzees to great apes, certain species appear to kiss. Now, researchers propose that Neanderthals did it too – and possibly exchanged kisses with early Homo sapiens.

Shared Oral Clues

This isn't the initial instance experts have proposed Neanderthals and Homo sapiens were intimately acquainted. In earlier research, scientists have found modern people and their Neanderthal relatives possessed the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, suggesting they swapped saliva.

"Likely they were engaging in intimate contact," the researcher noted, explaining that the idea aligned with studies that has revealed humans of non-African ancestry have bits of ancient genetic material in their genetic makeup, revealing interbreeding was occurring.

Intimate Interpretation

"It certainly puts a more romantic perspective on ancient interactions," the lead researcher commented.

Writing in the publication Evolution and Human Behavior, the researcher and colleagues detail how, to investigate the historical roots of kissing, they first had to come up with a description that was not limited to how people kiss.

Defining Intimate Contact

"Previously there were some previous attempts to describe a kiss, but it's largely focused on humans, which means that basically non-human species don't kiss. Now we know that they likely engage, it might just not look from what our intimate contact resembles," explained Brindle.

Nonetheless, she said some actions that looked like intimate contact were something rather different – such as the chewing and food sharing, or "kiss-fighting", seen in aquatic species known as certain marine animals.

As a result the team came up with a description of intimate contact centered around social behaviors involving directed oral interaction with a individual of the same species, with some movement of the oral area but no transfer of nutrition.

Research Methods

The lead researcher explained they concentrated on reports of intimate behavior in non-human species from Africa and Asia, including bonobos, apes and great apes, and used online videos to verify the reports.

Scientists then combined this data with details on the genetic connections between living and extinct types of such animals.

Evolutionary Origins

The team propose the results suggest intimate contact developed approximately 21.5 million and 16.9 million years ago in the predecessors of the great primates.

Placement of ancient hominins on this family tree means it is probable they, too, engaged in a intimate act, the researchers conclude. But the activity may not have been limited to their specific group.

"Reality that humans kiss, the fact that we now have shown that ancient relatives very likely engaged, indicates that the two [species] are also likely to have kissed," Brindle added.

Biological Importance

Although the scientific reasoning is discussed, Brindle explained kissing could be employed in sexual contexts to potentially enhance reproductive success or assist in selecting between partners, while it might help strengthen connections when used in a non-sexual manner.

A separate researcher in the behavior of great apes commented that as intimate contact was observed in a broad spectrum of primates it was logical its origins lie deep in our evolutionary past, and an analysis of different forms of kissing 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 examine carefully at other animals," he said.

Social Aspects

Another professor said 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 methods of promoting trust and intimacy will have been significant for eons," the professor stated. "This could represent an concept that appears a bit contradictory to our incorrect assumptions of a supposedly aggressive and aggressive past, but really it should be no surprise that ancient hominins – and even them and our human ancestors together – kissed."