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Among seabirds to polar bears, chimpanzees to great apes, various animals appear to kiss. Now, scientists suggest that Neanderthals did it too – and possibly exchanged kisses with early Homo sapiens.

Common Microbial Clues

It is not the first time experts have suggested Neanderthals and Homo sapiens were intimately acquainted. Among previous studies, researchers have found modern people and their thick-browed cousins possessed the same mouth microbe for millions of years after the evolutionary divergence, implying they swapped saliva.

"Probably they were kissing," she said, adding that the concept chimed with studies that has found humans of non-African ancestry have bits of Neanderthal DNA in their genetic makeup, revealing interbreeding was at play.

Romantic Interpretation

"This offers a different perspective on human-Neanderthal relations," Brindle said.

Publishing in the journal a scientific periodical, the researcher and colleagues detail how, to explore the historical roots of intimate contact, they first had to develop a definition that was not restricted by how people kiss.

Defining Kissing

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

However, she said some actions that resembled kissing were distinct activities – such as the processing and food sharing, or "mouth contact", observed in aquatic species called French grunts.

Consequently the research group developed a description of kissing based on friendly interactions involving directed mouth-to-mouth contact with a member of the identical group, with some movement of the mouth but no transfer of food.

Research Approach

Brindle explained they focused on accounts of intimate behavior in non-human species from Africa and Asia, including bonobos, chimpanzees and orangutans, and used online videos to confirm the observations.

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

Historical Origins

The team propose the results indicate kissing developed approximately 21.5m and 16.9 million years ago in the predecessors of the large apes.

Placement of Neanderthals on this family tree means it is probable they, too, engaged in a intimate act, the scientists conclude. But the behavior may not have been limited to their own species.

"The fact that modern people kiss, the reality that we now have demonstrated that Neanderthals probably engaged, suggests that the both groups are probably did engage," the researcher noted.

Evolutionary Significance

While the evolutionary explanation is discussed, the expert explained kissing could be employed in reproductive situations to possibly enhance mating outcomes or help choose between partners, while it could assist strengthen connections when used in a platonic way.

Another expert in the behavior of primates said that as intimate contact was seen in a wide range of apes it was logical its roots lie deep in our evolutionary past, and an examination of different forms of intimate behavior among a wider variety of species might push its beginnings back further still.

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

Social Elements

An archaeology expert said that intimate contact had a cultural element as it was not common to all societies.

"However, as people we thrive or fail on the quality of our emotional bonds, and ways of promoting confidence and intimacy will have been significant for millions of years," the professor stated. "It might be an image that appears a bit incongruous to our misplaced ideas of a rather ruthless and ancient history, but actually it should be expected that ancient hominins – and including Neanderthals and our own species collectively – engaged intimately."