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Among Galápagos albatrosses to polar bears, primates to orangutans, various animals engage in mouth-to-mouth contact. Now, scientists propose that ancient hominins also engaged in this behavior – and possibly locked lips with modern humans.

Shared Microbial Clues

This isn't the initial instance experts have proposed Neanderthals and Homo sapiens were intimately acquainted. Among earlier research, researchers have found humans and their Neanderthal relatives shared the same mouth microbe for millions of years after the evolutionary divergence, implying they swapped saliva.

"Likely they were kissing," the researcher noted, explaining that the concept aligned with studies that has revealed people of non-African ancestry have bits of ancient genetic material in their genome, revealing genetic mixing was occurring.

Intimate Interpretation

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

Writing in the journal a scientific periodical, the researcher and colleagues detail how, to investigate the historical roots of kissing, they first had to come up with a definition that was not limited to how humans kiss.

Describing Intimate Contact

"Previously there were some efforts to describe a intimate act, but it's very much been human-centric, which implies that essentially non-human species don't kiss. Now we understand that they probably do, it may appear different from what human kissing looks like," said the evolutionary biologist.

Nonetheless, she said some behaviors that looked like kissing were something rather different – such as the processing and food sharing, or "mouth contact", observed in aquatic species known as French grunts.

As a result the research group developed a definition of kissing centered around friendly interactions involving directed oral interaction with a individual of the identical group, with some motion of the mouth but absence of food.

Study Methods

Brindle said they focused on reports of intimate behavior in non-human species from Africa and Asia, including primates, apes and orangutans, and employed digital recordings to verify the observations.

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

Historical Origins

Researchers propose the findings suggest intimate contact developed approximately 21.5m and 16.9 million years ago in the ancestors of the great primates.

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

"The fact that modern people engage intimately, the fact that we currently have demonstrated that ancient relatives probably kissed, suggests that the both groups are also likely to have kissed," Brindle noted.

Biological Significance

Although the scientific reasoning is discussed, the expert explained intimate contact could be used in reproductive situations to potentially enhance mating outcomes or help choose between partners, while it could assist reinforce bonding when used in a platonic way.

Another expert in the activities of great apes commented that as intimate contact was seen in a broad spectrum of primates it was logical its origins lie deep in our ancient history, and an analysis of various types of intimate behavior among a broader range of animals might extend its beginnings back even earlier still.

"Things that we consider as signatures of human life, like intimate contact, are not exclusive to us if we examine carefully at different species," he said.

Cultural Elements

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

"Nonetheless, as people we thrive or fail on the quality of our relationships, and ways of encouraging confidence and intimacy will have been important for millions of years," she said. "It might be an image that appears a bit contradictory to our misplaced ideas of a supposedly aggressive and ancient history, but really it ought to be expected that ancient hominins – and even them and our own species collectively – engaged intimately."