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From Galápagos albatrosses to Arctic mammals, primates to great apes, certain species engage in mouth-to-mouth contact. Now, researchers suggest that Neanderthals also engaged in this behavior – and possibly locked lips with modern humans.

Common Microbial Evidence

This isn't the initial instance experts have proposed ancient relatives and Homo sapiens were closely connected. In previous studies, scientists have discovered modern people and their thick-browed cousins possessed the same mouth microbe for millions of years after the two species split, suggesting they exchanged oral fluids.

"Likely they were engaging in intimate contact," the researcher noted, explaining that the idea chimed with studies that has revealed people of certain genetic backgrounds have bits of ancient genetic material in their genome, demonstrating genetic mixing was at play.

Intimate Interpretation

"This offers a more romantic spin on ancient interactions," Brindle commented.

Writing in the publication a scientific periodical, Brindle and her team report how, to explore the evolutionary origins of kissing, they first had to come up with a description that was not restricted by how humans kiss.

Defining Intimate Contact

"Previously there were some efforts to define a kiss, but it's very much been focused on humans, which implies that basically non-human species do not engage in this. Now we understand that they probably do, it may appear different from what human kissing looks like," said the evolutionary biologist.

Nonetheless, she said some behaviors that looked like intimate contact were distinct activities – such as the chewing and transfer of food, or "kiss-fighting", seen in aquatic species called certain marine animals.

Consequently the team came up with a description of kissing based on social behaviors involving intentional oral interaction with a member of the identical group, with some motion of the mouth but no transfer of nutrition.

Research Approach

The lead researcher said they focused on accounts of kissing in non-human species from Africa and Asia, including primates, chimpanzees and orangutans, and used online videos to verify the reports.

Scientists then integrated this information with details on the genetic connections between living and extinct species of such primates.

Evolutionary Origins

Researchers propose the results suggest intimate contact evolved approximately 21.5 million and 16.9 million years ago in the ancestors of the large apes.

The position of ancient hominins on this family tree means it is probable they, too, engaged in a kiss, the researchers conclude. But the activity might not have been confined to their own species.

"Reality that modern people kiss, the reality that we now have demonstrated that Neanderthals probably kissed, indicates that the both groups are probably did engage," the researcher noted.

Evolutionary Importance

While the scientific reasoning is debated, Brindle said kissing could be employed in sexual contexts to potentially increase mating outcomes or help choose between partners, while it might help reinforce bonding when used in a platonic way.

Another expert in the activities of great apes said that as kissing behavior was observed in a broad spectrum of primates it made sense its roots extend far into our ancient history, and an analysis of different forms of kissing among a broader range of animals might extend its origins back even earlier still.

"Behaviors that we think of as signatures of our species, like intimate contact, are not unique to us if we look closely at other animals," he said.

Social Elements

Another professor explained that intimate contact had a social component as it was not common to all societies.

"Nonetheless, as humans we succeed or struggle on the quality of our emotional bonds, and methods of encouraging trust and closeness will have been important for eons," the professor stated. "It might be an image that seems a bit incongruous to our misplaced ideas of a supposedly aggressive and ancient history, but really it ought to be no surprise that Neanderthals – and even Neanderthals and our human ancestors together – kissed."