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Among seabirds to polar bears, chimpanzees to orangutans, certain species appear to kiss. Now, researchers propose that ancient hominins did it too – and might even have exchanged kisses with modern humans.

Common Microbial Evidence

This isn't the initial instance experts have suggested ancient relatives and Homo sapiens were closely connected. In earlier research, researchers have discovered humans and their Neanderthal relatives possessed the same mouth microbe for millions of years after the evolutionary divergence, implying they exchanged oral fluids.

"Probably they were kissing," she said, adding 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 Interpretation

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

Writing in the publication a scientific periodical, Brindle and colleagues detail how, to investigate the evolutionary origins of intimate contact, they first had to develop a definition that was not restricted by how humans kiss.

Defining Intimate Contact

"There have been some efforts to define a kiss, but it's largely human-centric, which implies that essentially non-human species do not engage in this. Currently we understand that they likely engage, it might just not look from what our intimate contact resembles," said Brindle.

Nonetheless, she said some actions that resembled intimate contact were distinct activities – such as the processing and transfer of food, or "mouth contact", seen in fish known as French grunts.

Consequently the team came up with a description of kissing centered around social behaviors involving intentional oral interaction with a individual of the identical group, with some movement of the mouth but absence of food.

Study Methods

Brindle explained they focused on accounts of intimate behavior in non-human species from Africa and Asian regions, including primates, apes and orangutans, and employed online videos to confirm the observations.

Scientists then integrated this information with details on the evolutionary relationships between extant and extinct species of such animals.

Historical Timeline

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

The position of ancient hominins on this evolutionary lineage means it is likely they, too, indulged in a intimate act, the researchers conclude. But the activity might 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, indicates that the two [species] are probably did kissed," the researcher noted.

Biological Importance

While the scientific reasoning is discussed, the expert said kissing could be used in sexual contexts to possibly enhance mating outcomes or assist in selecting between partners, while it could assist reinforce bonding when practiced in a platonic way.

Another expert in the activities of primates commented that as kissing behavior was observed 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 animals might push its origins back further still.

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

Cultural Aspects

An archaeology expert explained that kissing 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 confidence and intimacy will have been significant for eons," she said. "This could represent an concept that seems a bit incongruous to our incorrect assumptions of a supposedly aggressive and ancient history, but actually it ought to be no surprise that Neanderthals – and including Neanderthals and our own species together – kissed."