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From seabirds to Arctic mammals, chimpanzees to great apes, various animals appear to kiss. Now, scientists suggest that Neanderthals did it too – and might even have locked lips with early Homo sapiens.

Shared Microbial Clues

This isn't the initial instance experts have suggested Neanderthals and early modern humans were intimately acquainted. Among earlier research, scientists have found modern people and their Neanderthal relatives shared the identical oral bacteria for millions of years after the two species split, implying they exchanged oral fluids.

"Likely they were engaging in intimate contact," she said, adding that the idea chimed with studies that has revealed humans of non-African ancestry contain ancient genetic material in their genome, revealing genetic mixing was occurring.

Romantic Interpretation

"This offers a more romantic spin on human-Neanderthal relations," Brindle said.

Writing in the publication a scientific periodical, the researcher and colleagues report how, to investigate the historical roots of intimate contact, they first had to develop a description that was not limited to how humans smooch.

Defining Kissing

"Previously there were some previous attempts to describe a kiss, but it's largely focused on humans, which means that essentially non-human species do not engage in this. Now we know that they likely engage, it may appear different from what our intimate contact resembles," explained the evolutionary biologist.

Nonetheless, she noted some behaviors that looked like intimate contact were something rather different – such as the chewing and food sharing, or "kiss-fighting", seen in fish known as certain marine animals.

As a result the research group developed a description of kissing based on social behaviors involving directed oral interaction with a individual of the identical group, with some movement of the mouth but no transfer of nutrition.

Research Approach

The lead researcher said they concentrated on reports of intimate behavior in non-human species from Africa and Asia, including bonobos, apes and great apes, and employed digital recordings to confirm the reports.

Scientists then combined this data with information on the genetic connections between living and ancient species of such animals.

Historical Origins

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

The position of Neanderthals on this family tree suggests it is probable they, too, engaged in a kiss, the scientists conclude. But the activity may not have been limited to their specific group.

"Reality that modern people kiss, the fact that we currently have demonstrated that ancient relatives probably kissed, suggests that the both groups are probably did engage," Brindle noted.

Evolutionary Significance

Although the evolutionary explanation is discussed, Brindle explained intimate contact could be used in reproductive situations to potentially enhance reproductive success or assist in selecting between partners, while it might help strengthen connections when practiced in a non-sexual manner.

Another expert in the activities of primates commented that as intimate contact was observed in a broad spectrum of apes it was logical its roots extend far into our evolutionary past, and an analysis of various types of kissing among a broader range of animals might push its beginnings back even earlier still.

"Behaviors that we think of as signatures of human life, like intimate contact, are not unique to us if we examine carefully at different species," the expert noted.

Social Elements

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

"Nonetheless, as humans we thrive or fail on the quality of our relationships, and methods of encouraging confidence and closeness will have been significant for eons," the professor stated. "This could represent an image that appears a bit contradictory to our incorrect assumptions of a rather ruthless and ancient history, but really it ought to be expected that ancient hominins – and even them and our own species together – engaged intimately."