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From seabirds to Arctic mammals, chimpanzees to great apes, various animals engage in mouth-to-mouth contact. Now, scientists propose that Neanderthals did it too – and might even have locked lips with early Homo sapiens.

Common Oral Evidence

It is not the first time experts have proposed ancient relatives and early modern humans were intimately acquainted. Among previous studies, scientists have discovered modern people and their Neanderthal relatives possessed the identical oral bacteria for millions of years after the evolutionary divergence, implying they exchanged oral fluids.

"Probably they were engaging in intimate contact," she said, adding that the idea aligned with studies that has found people of non-African ancestry have bits of ancient genetic material in their genetic makeup, revealing interbreeding was at play.

Intimate Spin

"This offers a different spin on human-Neanderthal relations," the lead researcher said.

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

Describing Intimate Contact

"There have been some previous attempts to define a kiss, but it's very much been human-centric, which implies that basically other animals do not engage in this. Currently we understand that they likely engage, it may appear different from what human kissing resembles," said the evolutionary biologist.

Nonetheless, she noted some behaviors that resembled kissing were distinct activities – such as the processing and food sharing, or "kiss-fighting", observed in aquatic species known as French grunts.

As a result the research group developed a definition of intimate contact based on friendly interactions involving directed mouth-to-mouth contact with a individual of the same species, with some motion of the oral area but no transfer of nutrition.

Research Methods

The lead researcher said they focused on reports of kissing in non-human species from Africa and Asia, including primates, chimpanzees and orangutans, and employed online videos to confirm the observations.

The researchers then integrated this information with information on the genetic connections between extant and extinct species of such animals.

Evolutionary Timeline

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

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

"The fact that humans kiss, the fact that we now have shown that ancient relatives very likely kissed, suggests that the both groups are probably did engage," Brindle noted.

Biological Significance

Although the evolutionary explanation is discussed, the expert explained kissing could be employed in sexual contexts to possibly enhance reproductive success or assist in selecting between partners, while it could assist reinforce bonding when used in a non-sexual manner.

A separate researcher in the activities of great apes commented that as kissing behavior was observed in a wide range of apes it made sense its roots extend far into our evolutionary past, and an examination of different forms of kissing among a wider variety of animals might extend its beginnings back even earlier still.

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

Social Elements

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

"Nonetheless, as humans we thrive or fail on the quality of our emotional bonds, and ways of encouraging confidence and intimacy will have been important for eons," she said. "This could represent an image that appears a bit contradictory to our misplaced ideas of a rather ruthless and aggressive past, but really it ought to be expected that Neanderthals – and including Neanderthals and our own species collectively – engaged intimately."