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Among seabirds to Arctic mammals, primates to orangutans, various animals appear to kiss. Currently, researchers suggest that Neanderthals also engaged in this behavior – and might even have locked lips with early Homo sapiens.

Shared Oral Evidence

It is not the first time scientists have suggested ancient relatives and Homo sapiens were intimately acquainted. Among previous studies, scientists have found humans and their thick-browed cousins shared the identical oral bacteria for millions of years after the evolutionary divergence, implying they exchanged oral fluids.

"Likely they were engaging in intimate contact," the researcher noted, explaining that the concept chimed with studies that has revealed people of certain genetic backgrounds contain Neanderthal DNA in their genome, revealing interbreeding was at play.

Intimate Interpretation

"It certainly puts a more romantic spin on ancient interactions," the lead researcher commented.

Publishing in the journal a scientific periodical, the researcher and her team detail how, to explore the evolutionary origins of intimate contact, they first had to develop a description that was not restricted by how humans kiss.

Defining Kissing

"There have been some previous attempts to define a intimate act, but it's largely human-centric, which means that essentially non-human species do not engage in this. Now we know that they probably do, it may appear different from what human kissing resembles," explained Brindle.

Nonetheless, she said some actions that resembled kissing were something rather different – such as the processing and food sharing, or "mouth contact", seen in aquatic species known as certain marine animals.

As a result the team developed a definition of kissing based on social behaviors involving intentional oral interaction with a individual of the identical group, with some movement of the oral area but absence of nutrition.

Research Approach

Brindle said they concentrated on accounts of kissing in primates from Africa and Asia, including primates, chimpanzees and great apes, and employed digital recordings to verify the observations.

Scientists then integrated this data with details on the evolutionary relationships between living and ancient species of such primates.

Evolutionary Origins

Researchers say the results suggest intimate contact evolved somewhere between 21.5 million and 16.9 million years ago in the ancestors of the large apes.

Placement of ancient hominins on this evolutionary lineage suggests it is probable they, too, engaged in a intimate act, the researchers conclude. But the behavior may not have been confined to their own species.

"The fact that modern people kiss, the fact that we now have shown that ancient relatives probably kissed, indicates that the both groups are probably did engage," the researcher noted.

Evolutionary Importance

Although the evolutionary explanation is debated, the expert said intimate contact could be used in reproductive situations to possibly enhance mating outcomes or help choose between mates, while it might help reinforce bonding when used in a non-sexual manner.

Another expert in the behavior of great apes commented that as intimate contact was observed in a wide range of primates it made sense its roots extend far into our ancient history, and an analysis of various types of intimate behavior among a wider variety of species might push its beginnings back even earlier still.

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

Social Aspects

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

"Nonetheless, as people we thrive or fail on the strength of our relationships, and methods of encouraging confidence and intimacy will have been important for millions of years," the professor stated. "This could represent an concept that appears a bit contradictory to our misplaced ideas of a supposedly aggressive and ancient history, but really it should be expected that Neanderthals – and including Neanderthals and our own species together – engaged intimately."