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Among seabirds to Arctic mammals, chimpanzees to orangutans, various animals appear to kiss. Currently, scientists propose that Neanderthals also engaged in this behavior – and possibly exchanged kisses with early Homo sapiens.

Shared Oral Evidence

It is not the first time scientists have proposed Neanderthals and Homo sapiens were closely connected. Among previous studies, scientists have discovered humans and their thick-browed cousins possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Probably they were engaging in intimate contact," the researcher noted, explaining that the concept chimed with research that has revealed humans of certain genetic backgrounds contain Neanderthal DNA in their genetic makeup, revealing genetic mixing was occurring.

Intimate Interpretation

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

Writing in the publication a scientific periodical, Brindle and colleagues report how, to explore the evolutionary origins of intimate contact, they first had to develop a description that was not restricted by how people smooch.

Defining Intimate Contact

"There have been some previous attempts to define a intimate act, but it's largely human-centric, which implies that essentially other animals do not engage in this. Now we understand that they probably do, it might just not look from what human kissing looks like," said the evolutionary biologist.

Nonetheless, she noted some behaviors that looked like kissing were distinct activities – such as the processing and transfer of food, or "kiss-fighting", observed in aquatic species called certain marine animals.

Consequently the research group came up with a definition of kissing based on social behaviors involving intentional mouth-to-mouth contact with a individual of the identical group, with some movement of the mouth but absence of nutrition.

Research Approach

The lead researcher said they concentrated on accounts of kissing in non-human species from the African continent and Asia, including bonobos, chimpanzees and great apes, and used online videos to verify the reports.

Scientists then integrated this data with information on the genetic connections between extant and ancient species of such animals.

Historical Origins

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

Placement of Neanderthals on this family tree suggests 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.

"Reality that humans engage intimately, the reality that we currently have demonstrated that Neanderthals very likely kissed, suggests that the both groups are probably did kissed," Brindle added.

Biological Importance

While the scientific reasoning is debated, Brindle explained kissing could be used in reproductive situations to possibly enhance mating outcomes or help choose between partners, while it might help strengthen connections when practiced in a platonic way.

A separate researcher in the activities of great apes commented that as intimate contact was observed in a wide range of primates it made sense its roots lie deep in our evolutionary past, and an examination of various types of intimate behavior among a broader range of animals might push its origins back even earlier still.

"Things that we think of as characteristics of our species, like intimate contact, are not unique to us if we look closely at other animals," the expert noted.

Social Elements

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

"Nonetheless, as people we thrive or fail on the strength of our relationships, and methods of encouraging trust and closeness will have been significant for eons," the professor stated. "This could represent an image that seems a bit contradictory to our misplaced ideas of a rather ruthless and ancient history, but actually it ought to be no surprise that Neanderthals – and even them and our own species together – engaged intimately."