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Among seabirds to polar bears, chimpanzees to orangutans, various animals engage in mouth-to-mouth contact. Now, researchers propose that Neanderthals also engaged in this behavior – and might even have locked lips with early Homo sapiens.

Shared Microbial Clues

This isn't the initial instance scientists have suggested Neanderthals and early modern humans were intimately acquainted. Among earlier research, researchers have found modern people and their thick-browed cousins possessed the same mouth microbe for millions of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Likely they were engaging in intimate contact," she said, explaining that the concept chimed with studies that has revealed people of non-African ancestry have bits of Neanderthal DNA in their genetic makeup, revealing genetic mixing was occurring.

Romantic Interpretation

"This offers a different spin on human-Neanderthal relations," the lead researcher said.

Writing in the journal a scientific periodical, Brindle and colleagues report how, to explore the evolutionary origins of kissing, they first had to develop a description that was not limited to how humans kiss.

Describing Intimate Contact

"There have been some previous attempts to define a kiss, but it's largely focused on humans, which means that basically other animals don't kiss. Currently we know that they probably do, it might just not look from what our intimate contact looks like," said Brindle.

Nonetheless, she said some actions that resembled intimate contact were something rather different – such as the processing and food sharing, or "kiss-fighting", observed in fish called certain marine animals.

As a result the research group came up with a description of intimate contact centered around friendly interactions involving directed mouth-to-mouth contact with a individual of the same species, with some movement of the mouth but absence of food.

Research Methods

The lead researcher explained they focused on reports of intimate behavior in primates from the African continent and Asian regions, including primates, chimpanzees and great apes, and employed digital recordings to confirm the reports.

Scientists then integrated this information with information on the genetic connections between living and ancient types of such primates.

Evolutionary Timeline

The team propose the findings indicate intimate contact evolved approximately 21.5m and 16.9m years ago in the ancestors of the large apes.

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

"Reality that modern people engage intimately, the reality that we currently have shown that Neanderthals probably engaged, suggests that the two [species] are also likely to have kissed," Brindle noted.

Biological Significance

Although the evolutionary explanation is debated, the expert explained intimate contact could be used in reproductive situations to possibly enhance mating outcomes or assist in selecting between partners, while it might help strengthen connections when practiced in a non-sexual manner.

A separate researcher in the behavior of great apes commented that as intimate contact was observed in a wide range of apes it was logical its origins lie deep in our evolutionary past, and an examination of various types of intimate behavior among a wider variety of animals might push its beginnings back further still.

"Things that we think of as characteristics of human life, like intimate contact, are not unique to us if we look closely at different species," he said.

Social Aspects

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

"However, as people we succeed or struggle on the strength of our relationships, and methods of encouraging trust and intimacy will have been significant for eons," the professor stated. "This could represent an concept that seems a bit contradictory to our misplaced ideas of a rather ruthless and aggressive past, but actually it should be expected that ancient hominins – and even them and our own species together – engaged intimately."