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Among seabirds to polar bears, primates to orangutans, certain species appear to kiss. Currently, researchers suggest that ancient hominins also engaged in this behavior – and might even have locked lips with early Homo sapiens.

Shared Oral Evidence

It is not the first time experts have proposed ancient relatives and Homo sapiens were closely connected. Among earlier research, researchers have found modern people and their thick-browed cousins shared the identical oral bacteria for millions of years after the two species split, suggesting they swapped saliva.

"Likely they were engaging in intimate contact," she said, adding that the concept aligned with research that has found humans of certain genetic backgrounds have bits of Neanderthal DNA in their genome, revealing genetic mixing was at play.

Romantic Interpretation

"It certainly puts a different spin on human-Neanderthal relations," the lead researcher commented.

Publishing in the publication a scientific periodical, the researcher and her team detail how, to investigate the evolutionary origins of intimate contact, they first had to come up with a description that was not restricted by how people smooch.

Describing Intimate Contact

"There have been some efforts to describe a intimate act, but it's largely human-centric, which implies that essentially other animals do not engage in this. Currently we know that they probably do, it may appear different from what human kissing looks like," explained the evolutionary biologist.

Nonetheless, she said some behaviors that resembled kissing were something rather different – such as the processing and transfer of food, or "mouth contact", observed in fish known as certain marine animals.

Consequently the research group developed a definition of intimate contact centered around friendly interactions involving directed mouth-to-mouth contact with a member of the identical group, with some movement of the oral area but no transfer of nutrition.

Study Approach

The lead researcher said they concentrated on accounts of kissing in non-human species from Africa and Asian regions, including primates, apes and orangutans, and used digital recordings to confirm the reports.

The researchers then integrated this data with details on the genetic connections between extant and ancient types of such animals.

Evolutionary Origins

The team propose the results indicate intimate contact developed somewhere between 21.5 million and 16.9 million years ago in the predecessors of the great primates.

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

"The fact that humans kiss, the reality that we now have shown that ancient relatives probably engaged, suggests that the both groups are probably did kissed," the researcher added.

Biological Importance

While the scientific reasoning is debated, Brindle explained kissing could be employed in reproductive situations to potentially increase reproductive success or assist in selecting between partners, while it could assist strengthen connections when used in a non-sexual manner.

A separate researcher in the behavior of great apes said that as intimate contact was observed in a broad spectrum of primates it made sense its roots lie deep in our ancient history, and an analysis of various types of kissing among a broader range of species might push its origins back further still.

"Things that we consider as characteristics of our species, like kissing, are not unique to us if we examine carefully at different species," the expert noted.

Social Aspects

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

"However, as people we thrive or fail on the strength of our relationships, and methods of encouraging confidence and closeness will have been significant for eons," she said. "This could represent an image that appears a bit incongruous to our misplaced ideas of a rather ruthless and aggressive past, but actually it ought to be expected that Neanderthals – and including Neanderthals and our human ancestors collectively – kissed."