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From Galápagos albatrosses to polar bears, chimpanzees to great apes, various animals appear to kiss. Currently, scientists propose that ancient hominins did it too – and possibly exchanged kisses with early Homo sapiens.

Shared Oral Clues

This isn't the initial instance scientists have suggested ancient relatives and Homo sapiens were intimately acquainted. Among previous studies, researchers have discovered humans and their thick-browed cousins possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, implying they swapped saliva.

"Probably they were kissing," the researcher noted, adding that the idea chimed with studies that has revealed people of certain genetic backgrounds contain ancient genetic material in their genome, revealing interbreeding was occurring.

Intimate Interpretation

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

Publishing in the journal a scientific periodical, Brindle and colleagues detail how, to investigate the historical roots of intimate contact, they first had to come up with a description that was not limited to how people smooch.

Describing Kissing

"Previously there were some efforts to describe a intimate act, but it's very much been focused on humans, which implies that essentially non-human species do not engage in this. Now we understand that they probably do, it might just not look from what human kissing looks like," said Brindle.

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

Consequently the research group developed a definition of intimate contact based on friendly interactions involving directed oral interaction with a individual of the same species, with some movement of the mouth but no transfer of nutrition.

Study Approach

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

The researchers then integrated this information with information on the evolutionary relationships between extant and extinct types of such primates.

Historical Origins

The team propose the findings indicate intimate contact evolved somewhere between 21.5m and 16.9 million years ago in the ancestors of the large apes.

The position of Neanderthals on this evolutionary lineage means it is probable they, too, engaged in a intimate act, the scientists say. But the activity may not have been limited to their specific group.

"The fact that humans kiss, the reality that we currently have shown that ancient relatives very likely kissed, indicates that the both groups are also likely to have engage," the researcher added.

Biological Significance

Although the evolutionary explanation is discussed, the expert explained kissing could be used in reproductive situations to potentially increase mating outcomes or help choose between mates, while it could assist strengthen connections when practiced in a non-sexual manner.

Another expert in the activities of great apes commented that as kissing behavior was seen in a wide range of primates it made sense its roots lie deep in our evolutionary past, and an examination of various types of kissing among a broader range of animals might push its beginnings back further 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," he said.

Cultural Aspects

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

"However, as humans we succeed or struggle on the quality of our emotional bonds, and ways of promoting trust and intimacy will have been important for millions of years," the professor stated. "This could represent an concept that seems a bit contradictory to our incorrect assumptions of a supposedly aggressive and ancient history, but really it ought to be no surprise that Neanderthals – and even them and our own species together – kissed."