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From Galápagos albatrosses to Arctic mammals, primates to orangutans, certain species appear to kiss. Currently, scientists suggest that ancient hominins also engaged in this behavior – and might even have exchanged kisses with modern humans.

Shared Oral Evidence

It is not the first time experts have proposed Neanderthals and early modern humans were intimately acquainted. In previous studies, scientists have discovered modern people and their thick-browed cousins shared the identical oral bacteria for millions of years after the two species split, implying they swapped saliva.

"Probably they were kissing," the researcher noted, adding that the idea aligned with studies that has found humans of non-African ancestry contain ancient genetic material in their genetic makeup, demonstrating genetic mixing was at play.

Intimate Spin

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

Publishing in the journal a scientific periodical, the researcher and colleagues detail how, to explore the historical roots of intimate contact, they first had to develop a description that was not limited to how people kiss.

Defining Intimate Contact

"Previously there were some efforts to define a intimate act, but it's largely focused on humans, which means that essentially non-human species do not engage in this. Currently we understand that they probably do, it might just not look from what human kissing resembles," explained Brindle.

Nonetheless, she noted some behaviors that looked like kissing were something rather different – such as the chewing and food sharing, or "kiss-fighting", observed in fish known as French grunts.

As a result the team came up with a description of intimate contact based on friendly interactions involving directed mouth-to-mouth contact with a member of the identical group, with some movement of the mouth but absence of nutrition.

Research Methods

The lead researcher explained they focused on accounts of kissing in non-human species from Africa and Asia, including primates, chimpanzees and orangutans, and employed digital recordings to confirm the observations.

The researchers then integrated this information with information on the evolutionary relationships between living and ancient types of such primates.

Evolutionary Timeline

Researchers say the results suggest kissing evolved approximately 21.5 million and 16.9m years ago in the predecessors of the large apes.

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

"The fact that humans engage intimately, the reality that we currently have shown that ancient relatives very likely engaged, indicates that the two [species] are probably did kissed," the researcher noted.

Biological Importance

While the evolutionary explanation is debated, the expert explained intimate contact could be employed in reproductive situations to potentially increase mating outcomes or assist in selecting between mates, while it could assist strengthen connections when practiced in a non-sexual manner.

Another expert in the behavior of primates said that as intimate contact was observed in a wide range of apes it made sense its roots lie deep in our evolutionary past, and an analysis of different forms of intimate behavior among a broader range of animals might push its origins back further still.

"Things that we consider as characteristics of our species, like intimate contact, are not unique to us if we examine carefully at other animals," he said.

Cultural Aspects

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

"Nonetheless, as humans we thrive or fail on the quality of our emotional bonds, and ways of promoting trust and intimacy will have been significant for millions of years," the professor stated. "It might be an image that appears a bit contradictory to our misplaced ideas of a rather ruthless and aggressive past, but actually it should be expected that Neanderthals – and including them and our human ancestors together – engaged intimately."