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From Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, certain species appear to kiss. Now, scientists suggest that ancient hominins did it too – and possibly locked lips with early Homo sapiens.

Shared Microbial Evidence

It is not the first time experts have suggested ancient relatives and early modern humans were closely connected. Among previous studies, researchers have found humans and their thick-browed cousins shared the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Probably they were kissing," she said, adding that the concept chimed with studies that has found humans of certain genetic backgrounds have bits of ancient genetic material in their genetic makeup, revealing interbreeding was at play.

Intimate Interpretation

"This offers a different perspective on ancient interactions," Brindle commented.

Publishing in the publication a scientific periodical, Brindle and her team report how, to explore the evolutionary origins of intimate contact, they first had to come up with a description that was not restricted by how humans kiss.

Defining Intimate Contact

"There have been some previous attempts to define a intimate act, but it's largely human-centric, which means that essentially other animals don't kiss. Now we know that they likely engage, it might just not look from what human kissing looks like," said the evolutionary biologist.

Nonetheless, she said some behaviors that looked like intimate contact were distinct activities – such as the chewing and transfer of food, or "mouth contact", observed in fish called French grunts.

Consequently the team developed a description of kissing centered around social behaviors involving directed mouth-to-mouth contact with a member of the same species, with some movement of the oral area but no transfer of nutrition.

Research Methods

The lead researcher explained they concentrated on reports of kissing in primates from the African continent and Asian regions, including bonobos, apes and orangutans, and employed online videos to verify the observations.

Scientists then combined this data with details on the genetic connections between extant and ancient species of such animals.

Historical Origins

The team propose the results suggest kissing developed somewhere between 21.5 million and 16.9m years ago in the predecessors of the great primates.

The position of Neanderthals on this evolutionary lineage suggests it is likely they, too, engaged in a kiss, the researchers conclude. But the activity might not have been confined to their specific group.

"Reality that modern people kiss, the fact that we now have shown that Neanderthals very likely kissed, indicates that the two [species] are probably did kissed," Brindle added.

Evolutionary Importance

Although the evolutionary explanation is discussed, Brindle said intimate contact could be employed in reproductive situations to possibly increase reproductive success or assist in selecting between mates, while it might help strengthen connections when used in a platonic way.

Another expert in the activities of great apes commented that as intimate contact was seen in a wide range of primates it was logical its origins lie deep in our evolutionary past, and an analysis of various types of intimate behavior among a broader range of species might extend its beginnings back further still.

"Things that we consider as signatures of human life, like intimate contact, are not exclusive to us if we look closely at different species," he said.

Social Aspects

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

"Nonetheless, as humans we thrive or fail on the strength of our emotional bonds, and ways of promoting trust and intimacy will have been significant for eons," the professor stated. "This could represent an concept that appears a bit incongruous to our misplaced ideas of a supposedly aggressive and aggressive past, but really it ought to be no surprise that ancient hominins – and including Neanderthals and our human ancestors together – engaged intimately."