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Among Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, various animals appear to kiss. Currently, researchers propose that Neanderthals did it too – and possibly locked lips with early Homo sapiens.

Common Oral Evidence

It is not the first time experts have suggested ancient relatives and Homo sapiens were intimately acquainted. Among earlier research, scientists have discovered modern people and their Neanderthal relatives possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Likely they were engaging in intimate contact," she said, adding that the concept chimed with studies that has revealed humans of certain genetic backgrounds have bits of ancient genetic material in their genetic makeup, demonstrating genetic mixing was at play.

Intimate Spin

"This offers a different perspective on human-Neanderthal relations," the lead researcher commented.

Publishing in the journal a scientific periodical, Brindle and her team report how, to investigate the historical roots of intimate contact, they first had to develop a definition that was not restricted by how humans smooch.

Defining Intimate Contact

"There have been some efforts to define a kiss, but it's very much been human-centric, which implies that essentially non-human species do not engage in this. Currently we know that they likely engage, it might just not look from what human kissing resembles," explained the evolutionary biologist.

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

As a result the team developed a description of intimate contact based on social behaviors involving directed oral interaction with a member of the identical group, with some movement of the oral area but absence of nutrition.

Research Approach

The lead researcher said they concentrated on accounts of kissing in primates from the African continent and Asia, including primates, chimpanzees and orangutans, and used online videos to confirm the observations.

Scientists then combined this information with details on the evolutionary relationships between extant and extinct species of such primates.

Evolutionary Origins

The team propose the findings indicate intimate contact developed approximately 21.5m and 16.9m years ago in the ancestors of the great primates.

Placement of Neanderthals on this evolutionary lineage means it is probable they, too, indulged in a intimate act, the researchers say. But the behavior might not have been confined to their specific group.

"Reality that humans kiss, the fact that we now have demonstrated that Neanderthals probably engaged, suggests that the two [species] are probably did engage," Brindle added.

Evolutionary Significance

While the evolutionary explanation is debated, the expert explained intimate contact could be employed in sexual contexts to possibly enhance mating outcomes or assist in selecting between partners, while it might help strengthen connections when practiced in a platonic way.

A separate researcher in the activities of primates commented that as intimate contact was observed in a broad spectrum of primates it made sense its roots lie deep in our evolutionary past, and an examination of various types of intimate behavior among a wider variety of animals might push its beginnings back further still.

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

Social Aspects

Another professor said that kissing had a cultural element as it was not common to all societies.

"However, as humans we succeed or struggle on the quality of our relationships, and ways of encouraging trust and intimacy will have been important for millions of years," the professor stated. "It might be an concept that seems a bit contradictory to our incorrect assumptions of a rather ruthless and aggressive past, but really it ought to be no surprise that ancient hominins – and even them and our own species together – kissed."