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Among Galápagos albatrosses to polar bears, chimpanzees to great apes, various animals engage in mouth-to-mouth contact. Now, researchers propose that ancient hominins did it too – and might even have locked lips with early Homo sapiens.

Shared Microbial Evidence

It is not the first time scientists have proposed ancient relatives and early modern humans were intimately acquainted. In earlier research, researchers have discovered humans and their thick-browed cousins possessed the same mouth microbe for hundreds of thousands 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 research that has found humans of certain genetic backgrounds have bits of Neanderthal DNA in their genome, revealing genetic mixing was occurring.

Romantic Spin

"It certainly puts a more romantic spin on ancient interactions," the lead researcher said.

Writing in the journal a scientific periodical, the researcher and her team detail how, to explore the historical roots of kissing, they first had to develop a description that was not limited to how humans smooch.

Defining Intimate Contact

"There have been some previous attempts to describe a kiss, but it's very much been focused on humans, which means that basically other animals don't kiss. Currently we know that they probably do, it may appear different from what our intimate contact resembles," said the evolutionary biologist.

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

Consequently the research group developed a definition of kissing based on friendly interactions involving intentional mouth-to-mouth contact with a member of the same species, with some motion of the oral area but no transfer of food.

Study Approach

Brindle explained they concentrated on reports of kissing in primates from the African continent and Asian regions, including primates, apes and orangutans, and employed digital recordings to verify the observations.

The researchers then integrated this information with details on the genetic connections between living and extinct species of such animals.

Evolutionary Timeline

The team say the findings indicate kissing evolved approximately 21.5 million and 16.9m years ago in the predecessors of the large apes.

The position of Neanderthals on this evolutionary lineage suggests it is likely they, too, indulged in a intimate act, the scientists conclude. But the activity may not have been limited to their own species.

"Reality that humans kiss, the reality that we now have demonstrated that ancient relatives very likely engaged, indicates that the both groups are also likely to have kissed," Brindle noted.

Biological Importance

While the evolutionary explanation is debated, Brindle said kissing could be used in reproductive situations to possibly enhance mating outcomes or help choose between mates, while it might help strengthen connections when used in a platonic way.

A separate researcher in the activities of great apes commented that as intimate contact was seen in a broad spectrum of apes it made sense its origins lie deep in our ancient history, and an analysis of different forms of intimate behavior among a broader range of species might extend its beginnings back further still.

"Things that we think of as characteristics of human life, like intimate contact, are not exclusive to us if we look closely at other animals," the expert noted.

Social Elements

An archaeology expert explained that kissing had a cultural element as it was not universal to all societies.

"However, as humans we succeed or struggle on the strength of our emotional bonds, and ways of promoting trust and closeness will have been significant for millions of years," the professor stated. "It might be an image that seems a bit contradictory to our incorrect assumptions of a supposedly aggressive and ancient history, but actually it ought to be expected that ancient hominins – and including Neanderthals and our own species together – kissed."