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From Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, certain species engage in mouth-to-mouth contact. Currently, researchers propose that Neanderthals did it too – and possibly locked lips with early Homo sapiens.

Shared Oral Evidence

This isn't the initial instance experts have proposed ancient relatives and early modern humans were closely connected. Among previous studies, scientists have discovered 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 kissing," she said, explaining that the idea chimed with research that has found humans of certain genetic backgrounds have bits of Neanderthal DNA in their genetic makeup, revealing interbreeding was at play.

Intimate Interpretation

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

Publishing in the journal a scientific periodical, Brindle and her team detail how, to investigate the evolutionary origins of intimate contact, they first had to come up with a definition that was not limited to how humans smooch.

Defining Kissing

"There have been some previous attempts to describe a kiss, but it's very much been human-centric, which means that essentially other animals do not engage in this. Now we know that they probably do, it may appear different from what our intimate contact looks like," explained Brindle.

However, she said some behaviors that resembled kissing were distinct activities – such as the chewing and transfer of food, or "kiss-fighting", observed in aquatic species called French grunts.

As a result the team came up with a description of kissing centered around social behaviors involving directed mouth-to-mouth contact with a member of the same species, with some movement of the oral area but no transfer of food.

Study Approach

Brindle said they concentrated on reports of kissing in primates from the African continent and Asia, including primates, chimpanzees and great apes, and employed digital recordings to verify the reports.

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

Historical Timeline

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

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

"The fact that modern people kiss, the fact that we now have shown that ancient relatives very likely kissed, indicates that the two [species] are also likely to have kissed," the researcher noted.

Biological Importance

Although the scientific reasoning is discussed, the expert said intimate contact could be employed in reproductive situations to potentially enhance reproductive success or help choose between partners, while it might help reinforce bonding when practiced in a platonic way.

A separate researcher in the behavior of great apes said that as intimate contact was seen in a wide range of primates it was logical its roots lie deep in our ancient history, and an analysis of various types of kissing among a broader range of animals might push its beginnings back even earlier still.

"Behaviors that we consider as signatures of our species, like intimate contact, are not unique to us if we examine carefully at different species," the expert noted.

Social Elements

Another professor explained that kissing had a cultural element as it was not common to all human groups.

"However, as humans we thrive or fail on the strength of our emotional bonds, and methods of encouraging trust and closeness 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 ancient history, but actually it ought to be expected that ancient hominins – and even Neanderthals and our human ancestors collectively – kissed."