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From Galápagos albatrosses to polar bears, primates to great apes, certain species appear to kiss. Now, researchers suggest that ancient hominins did it too – and possibly exchanged kisses with early Homo sapiens.

Common Oral Clues

It is not the first time experts have proposed Neanderthals and Homo sapiens were intimately acquainted. Among earlier research, researchers have discovered modern people and their Neanderthal relatives shared the identical oral bacteria for millions of years after the two species split, implying they exchanged oral fluids.

"Likely they were kissing," the researcher noted, explaining that the idea aligned with studies that has found people of certain genetic backgrounds contain ancient genetic material in their genome, revealing interbreeding was at play.

Intimate Interpretation

"This offers a more romantic perspective on human-Neanderthal relations," Brindle said.

Writing in the publication a scientific periodical, the researcher and colleagues detail how, to investigate the historical roots of intimate contact, they first had to develop a description that was not limited to how humans smooch.

Describing Intimate Contact

"Previously there were some previous attempts to describe a kiss, but it's very much been focused on humans, which implies that essentially other animals don't kiss. Now we know that they probably do, it may appear different from what human kissing resembles," explained Brindle.

However, she noted some behaviors that resembled intimate contact were something rather different – such as the chewing and transfer of food, or "mouth contact", seen in aquatic species known as certain marine animals.

Consequently the research group came up with a description of intimate contact centered around social behaviors involving intentional mouth-to-mouth contact with a individual of the identical group, with some motion of the mouth but no transfer of food.

Study Approach

Brindle explained they focused on accounts of kissing in non-human species from Africa and Asian regions, including bonobos, apes and great apes, and employed online videos to confirm the observations.

The researchers then combined this data with information on the genetic connections between extant and ancient species of such primates.

Historical Origins

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

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

"The fact that humans kiss, the reality that we now have demonstrated that ancient relatives probably engaged, suggests that the two [species] are also likely to have kissed," Brindle added.

Evolutionary Importance

While the evolutionary explanation is debated, the expert explained intimate contact could be used in sexual contexts to potentially enhance mating outcomes or assist in selecting between partners, while it might help reinforce bonding when practiced in a platonic way.

Another expert in the behavior of great apes said that as kissing behavior was seen in a broad spectrum of apes it was logical its roots extend far into our ancient history, and an examination of various types of kissing among a wider variety of species might extend its beginnings back further still.

"Things that we think of as signatures of our species, like intimate contact, are not exclusive to us if we look closely at different species," the expert noted.

Cultural Aspects

Another professor said that intimate contact had a cultural element as it was not common to all societies.

"However, as people we succeed or struggle on the quality of our relationships, and methods of promoting trust and closeness will have been significant for eons," she said. "This could represent an image that appears a bit incongruous to our incorrect assumptions of a rather ruthless and ancient history, but really it ought to be expected that Neanderthals – and including Neanderthals and our human ancestors collectively – kissed."