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From Galápagos albatrosses to polar bears, chimpanzees to great apes, certain species appear to kiss. Now, researchers propose that Neanderthals did it too – and possibly locked lips with modern humans.

Shared Oral Clues

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

"Probably they were engaging in intimate contact," she said, adding that the concept chimed with studies that has found humans of certain genetic backgrounds contain ancient genetic material in their genetic makeup, demonstrating genetic mixing was at play.

Romantic Interpretation

"This offers a more romantic spin on ancient interactions," the lead researcher commented.

Writing in the journal Evolution and Human Behavior, Brindle and her team report how, to investigate the historical roots of kissing, they first had to come up with a description that was not limited to how people smooch.

Defining Intimate Contact

"There have been some previous attempts to define a kiss, but it's very much been human-centric, which implies that essentially other animals do not engage in this. Now we know that they probably do, it may appear different from what human kissing looks like," explained Brindle.

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

Consequently the research group developed a definition of intimate contact based on social behaviors involving directed oral interaction with a individual of the same species, with some motion of the oral area but no transfer of food.

Research Approach

The lead researcher said they concentrated on reports of kissing in primates from Africa and Asian regions, including primates, chimpanzees and orangutans, and used digital recordings to verify the observations.

The researchers then combined this information with information on the evolutionary relationships between living and extinct species of such primates.

Historical Timeline

The team propose the results indicate intimate contact evolved approximately 21.5m and 16.9 million years ago in the ancestors of the great primates.

The position of Neanderthals on this evolutionary lineage means it is probable they, too, engaged in a intimate act, the researchers conclude. But the behavior might not have been limited to their own species.

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

Evolutionary Significance

While the scientific reasoning is debated, Brindle said kissing could be used in reproductive situations to possibly increase reproductive success or help choose between partners, while it might help strengthen connections when practiced in a platonic way.

A separate researcher in the activities of great apes said that as kissing behavior was observed in a broad spectrum of apes it made sense its origins lie deep in our evolutionary past, and an analysis of different forms of intimate behavior among a broader range of animals might extend its beginnings back even earlier still.

"Things that we think of as characteristics of our species, like intimate contact, are not exclusive to us if we look closely at different species," the expert noted.

Social Aspects

Another professor said that kissing had a social component as it was not common to all human groups.

"However, as people we thrive or fail on the strength of our emotional bonds, and methods of encouraging trust and closeness will have been significant for eons," she said. "It might be an concept that appears a bit contradictory to our incorrect assumptions of a rather ruthless and ancient history, but really it should be expected that ancient hominins – and including them and our own species collectively – kissed."