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Among seabirds to Arctic mammals, primates to orangutans, certain species engage in mouth-to-mouth contact. Now, scientists suggest that Neanderthals also engaged in this behavior – and might even have exchanged kisses with modern humans.

Common Microbial Clues

It is not the first time scientists have proposed ancient relatives and Homo sapiens were closely connected. In previous studies, researchers have discovered modern people and their thick-browed cousins possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, implying they exchanged oral fluids.

"Likely they were engaging in intimate contact," the researcher noted, explaining that the concept aligned with studies that has revealed humans of certain genetic backgrounds contain ancient genetic material in their genetic makeup, demonstrating genetic mixing was occurring.

Intimate Interpretation

"It certainly puts a different spin on ancient interactions," Brindle commented.

Publishing in the journal a scientific periodical, Brindle and her team detail how, to investigate the historical roots of kissing, they first had to come up with a description that was not restricted by how humans smooch.

Defining Intimate Contact

"There have been some efforts to describe a kiss, but it's very much been focused on humans, which means that essentially non-human species don't kiss. Currently we understand that they likely engage, it may appear different from what our intimate contact resembles," said the evolutionary biologist.

Nonetheless, she said some actions that looked like intimate contact were distinct activities – such as the chewing and food sharing, or "mouth contact", seen in aquatic species known as French grunts.

As a result the team came up with a definition of kissing based on social behaviors involving intentional oral interaction with a member of the identical group, with some motion of the oral area but absence of nutrition.

Study Approach

The lead researcher said they concentrated on accounts of kissing in non-human species from the African continent and Asian regions, including bonobos, apes and orangutans, and employed online videos to verify the reports.

Scientists then combined this information with information on the evolutionary relationships between extant and ancient types of such animals.

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.

The position of ancient hominins on this evolutionary lineage means it is probable they, too, engaged in a kiss, the researchers say. But the activity might not have been limited to their own species.

"Reality that humans kiss, the reality that we now have demonstrated that ancient relatives very likely kissed, indicates that the both groups are probably did kissed," the researcher added.

Evolutionary Importance

Although the scientific reasoning is discussed, the expert said kissing could be employed in sexual contexts to possibly increase reproductive success or help choose between mates, while it might help reinforce bonding when used in a platonic way.

Another expert in the activities of great apes commented that as intimate contact was observed in a wide range of primates it was logical its origins extend far into our evolutionary past, and an examination of different forms of kissing among a wider variety of animals might push its beginnings back even earlier 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.

Social Elements

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

"However, as humans we succeed or struggle on the quality of our relationships, and ways of promoting trust and closeness will have been important for millions of years," she said. "This could represent an image that appears a bit contradictory to our incorrect assumptions of a rather ruthless and ancient history, but actually it should be expected that Neanderthals – and even them and our own species collectively – engaged intimately."