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From seabirds to polar bears, primates to orangutans, various animals appear to kiss. Currently, researchers propose that Neanderthals did it too – and possibly exchanged kisses with early Homo sapiens.

Common Oral Evidence

This isn't the initial instance experts have suggested ancient relatives and Homo sapiens were closely connected. Among previous studies, scientists have found modern people and their thick-browed cousins shared the same mouth microbe for hundreds of thousands of years after the two species split, implying they exchanged oral fluids.

"Probably they were kissing," the researcher noted, explaining that the concept chimed with research that has revealed people of certain genetic backgrounds have bits of ancient genetic material in their genetic makeup, demonstrating genetic mixing was at play.

Romantic Spin

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

Publishing in the publication a scientific periodical, the researcher and colleagues detail how, to investigate the evolutionary origins of intimate contact, they first had to come up with a definition that was not limited to how humans kiss.

Describing Intimate Contact

"Previously there were some efforts to describe a intimate act, but it's largely human-centric, which implies that basically non-human species don't kiss. Now we understand that they likely engage, it might just not look from what our intimate contact resembles," said the evolutionary biologist.

However, she noted some behaviors that looked like intimate contact were something rather different – such as the chewing and food sharing, or "mouth contact", seen in fish known as certain marine animals.

As a result the research group developed a description of kissing based on friendly interactions involving intentional oral interaction with a member of the identical group, with some movement of the oral area but no transfer of food.

Research Methods

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

Scientists then combined this information with details on the evolutionary relationships between living and extinct types of such animals.

Historical Timeline

The team propose the findings indicate kissing evolved somewhere between 21.5m and 16.9 million years ago in the predecessors of the great primates.

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

"The fact that modern people kiss, the fact that we now have demonstrated that ancient relatives very likely kissed, indicates that the two [species] are probably did engage," Brindle added.

Biological Significance

Although the evolutionary explanation is discussed, Brindle explained kissing could be used in reproductive situations to potentially increase mating outcomes or help choose between partners, while it might help strengthen connections when practiced in a platonic way.

Another expert in the behavior of primates commented that as intimate contact was seen in a broad spectrum of apes it made sense its origins extend far into our ancient history, and an analysis of different forms of intimate behavior among a wider variety of species might push its origins back even earlier still.

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

Cultural Elements

An archaeology expert explained that intimate contact had a cultural element as it was not common to all human groups.

"Nonetheless, as humans we thrive or fail on the strength of our relationships, and ways of promoting trust and closeness will have been significant for eons," the professor stated. "It might be an image that seems a bit incongruous to our incorrect assumptions of a supposedly aggressive and ancient history, but really it should be expected that ancient hominins – and even them and our own species together – kissed."