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Among Galápagos albatrosses to polar bears, primates to orangutans, certain species appear to kiss. Currently, scientists suggest that ancient hominins did it too – and might even have locked lips with early Homo sapiens.

Shared Oral Evidence

It is not the first time scientists have proposed Neanderthals and early modern humans were closely connected. Among earlier research, scientists have discovered modern people and their thick-browed cousins shared the identical oral bacteria for hundreds of thousands of years after the two species split, implying they exchanged oral fluids.

"Likely they were kissing," she said, adding that the concept aligned with research that has found people of certain genetic backgrounds contain ancient genetic material in their genome, revealing genetic mixing was occurring.

Romantic Spin

"It certainly puts a different spin on ancient interactions," Brindle said.

Publishing in the publication a scientific periodical, the researcher and colleagues report how, to explore the historical roots of kissing, they first had to come up with a definition that was not limited to how people kiss.

Defining Intimate Contact

"Previously there were some previous attempts to describe a kiss, but it's very much been focused on humans, which implies that essentially other animals do not engage in this. Now we understand that they likely engage, it may appear different from what human kissing looks like," said Brindle.

Nonetheless, she noted some behaviors that looked like kissing were distinct activities – such as the processing and transfer of food, or "kiss-fighting", seen in fish called French grunts.

Consequently the research group came up with a definition of kissing based on social behaviors involving directed oral interaction with a individual of the identical group, with some movement of the mouth but absence of nutrition.

Research Approach

The lead researcher explained they focused on accounts of intimate behavior in primates from Africa and Asian regions, including bonobos, apes and great apes, and employed digital recordings to verify the observations.

Scientists then combined this data with information on the evolutionary relationships between living and ancient types of such primates.

Evolutionary Timeline

Researchers say the findings indicate intimate contact evolved approximately 21.5 million and 16.9m years ago in the predecessors of the great primates.

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

"Reality that humans engage intimately, the fact that we currently have shown that Neanderthals probably engaged, indicates that the both groups are probably did engage," Brindle noted.

Evolutionary Significance

Although the evolutionary explanation is debated, Brindle explained kissing could be employed in reproductive situations to potentially enhance reproductive success or help choose between partners, while it could assist strengthen connections when used in a platonic way.

A separate researcher in the activities of great apes said that as kissing behavior was seen in a wide range of apes it was logical its roots extend far into our ancient history, and an examination of different forms of intimate behavior among a broader range of animals might extend its origins back further still.

"Things that we consider as signatures of human life, like intimate contact, are not exclusive to us if we examine carefully at other animals," he said.

Cultural Aspects

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

"Nonetheless, as humans we succeed or struggle on the strength of our relationships, and methods of promoting confidence and intimacy will have been important for eons," the professor stated. "It might be an concept that seems a bit incongruous to our incorrect assumptions of a supposedly aggressive and aggressive past, but actually it ought to be expected that ancient hominins – and even them and our human ancestors collectively – kissed."