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From Galápagos albatrosses to polar bears, chimpanzees to orangutans, various animals engage in mouth-to-mouth contact. Now, researchers suggest that Neanderthals did it too – and possibly locked lips with early Homo sapiens.

Shared Oral Clues

This isn't the initial instance scientists have proposed Neanderthals and early modern humans were intimately acquainted. Among previous studies, researchers have found modern people and their thick-browed cousins possessed the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Likely they were engaging in intimate contact," she said, explaining that the idea chimed with research that has revealed people of non-African ancestry contain ancient genetic material in their genetic makeup, demonstrating genetic mixing was at play.

Romantic Spin

"This offers a more romantic spin on ancient interactions," Brindle commented.

Publishing in the journal a scientific periodical, Brindle and her team detail how, to explore the historical roots of kissing, they first had to come up with a definition that was not restricted by how people smooch.

Describing Kissing

"There have been some previous attempts to describe a intimate act, but it's very much been human-centric, which implies that essentially non-human species don't kiss. Now we understand that they likely engage, it may appear different from what our intimate contact resembles," said Brindle.

However, she said some behaviors that resembled kissing were something rather different – such as the processing and food sharing, or "kiss-fighting", observed in fish known as French grunts.

Consequently the team came up with 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 absence of nutrition.

Research Approach

The lead researcher explained they concentrated on accounts of intimate behavior in non-human species from Africa and Asia, including primates, apes and orangutans, and used digital recordings to confirm the reports.

The researchers then integrated this data with details on the evolutionary relationships between extant and extinct types of such animals.

Historical Origins

Researchers propose the findings suggest kissing developed somewhere between 21.5m and 16.9 million years ago in the predecessors of the large apes.

Placement of ancient hominins on this family tree means it is probable they, too, engaged in a intimate act, the researchers say. But the behavior might not have been confined to their specific group.

"The fact that modern people engage intimately, the reality that we now have demonstrated that ancient relatives probably kissed, indicates that the two [species] are also likely to have kissed," Brindle added.

Evolutionary Significance

Although the scientific reasoning is discussed, the expert explained kissing could be used in sexual contexts to potentially enhance mating outcomes or assist in selecting between mates, while it could assist reinforce bonding when used in a non-sexual manner.

A separate researcher in the behavior of primates said that as intimate contact was seen in a broad spectrum of primates it was logical its roots extend far into our evolutionary past, and an examination of various types of kissing among a wider variety of species might extend its origins back further still.

"Behaviors that we consider as characteristics of our species, like intimate contact, are not unique to us if we look closely at different species," he said.

Social Aspects

Another professor said that intimate contact had a cultural element as it was not common to all human groups.

"Nonetheless, as people we thrive or fail on the quality of our relationships, and methods of encouraging trust and intimacy will have been important for millions of years," the professor stated. "It might be an image that seems a bit contradictory to our misplaced ideas of a rather ruthless and aggressive past, but actually it should be no surprise that Neanderthals – and including Neanderthals and our human ancestors together – kissed."