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From Galápagos albatrosses to polar bears, chimpanzees to orangutans, certain species appear to kiss. Currently, scientists suggest that ancient hominins did it too – and might even have locked lips with early Homo sapiens.

Shared Oral Clues

It is not the first time experts have suggested Neanderthals and early modern humans were intimately acquainted. In previous studies, researchers have found modern people and their thick-browed cousins possessed the identical oral bacteria for hundreds of thousands of years after the two species split, suggesting they swapped saliva.

"Probably they were kissing," the researcher noted, adding that the idea aligned with studies that has found humans of certain genetic backgrounds contain ancient genetic material in their genetic makeup, revealing interbreeding was at play.

Intimate Spin

"It certainly puts a different spin on human-Neanderthal relations," the lead researcher commented.

Publishing in the publication a scientific periodical, the researcher and colleagues report how, to investigate the historical roots of kissing, they first had to develop a description that was not limited to how people kiss.

Defining Kissing

"Previously there were some previous attempts to define a kiss, but it's largely human-centric, which implies that essentially other animals do not engage in this. Now we know that they likely engage, it might just not look from what our intimate contact resembles," explained Brindle.

However, she said some behaviors that looked like intimate contact were distinct activities – such as the chewing and food sharing, or "mouth contact", seen in fish called French grunts.

As a result the research group developed a description of intimate contact based on social behaviors involving directed mouth-to-mouth contact with a individual of the identical group, with some motion of the mouth but absence of food.

Research Approach

The lead researcher said they concentrated on reports of intimate behavior in non-human species from Africa and Asia, including bonobos, chimpanzees and orangutans, and used online videos to verify the observations.

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

Historical Origins

Researchers propose the findings suggest intimate contact developed somewhere between 21.5 million and 16.9m years ago in the ancestors of the large apes.

The position of Neanderthals on this evolutionary lineage means it is probable they, too, indulged in a intimate act, the scientists conclude. 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 engage," the researcher added.

Evolutionary Importance

While the evolutionary explanation is discussed, Brindle explained kissing could be used in reproductive situations to potentially increase reproductive success or assist in selecting between mates, while it could assist reinforce bonding when used in a platonic way.

Another expert in the behavior of primates said that as intimate contact was observed in a broad spectrum of primates it made sense its roots extend far into our evolutionary past, and an analysis of different forms of kissing among a wider variety of animals might push its beginnings back even earlier still.

"Behaviors that we think of as characteristics of human life, like intimate contact, are not unique to us if we examine carefully at different species," the expert noted.

Social Elements

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

"Nonetheless, as people we succeed or struggle on the quality of our emotional bonds, and ways of encouraging confidence and closeness will have been significant for millions of years," the professor stated. "This could represent an concept that appears a bit contradictory to our incorrect assumptions of a rather ruthless and aggressive past, but really it ought to be expected that Neanderthals – and including them and our human ancestors collectively – engaged intimately."