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From Galápagos albatrosses to polar bears, chimpanzees to great apes, various animals appear to kiss. Currently, researchers propose that Neanderthals did it too – and might even have exchanged kisses with early Homo sapiens.

Shared Oral Evidence

It is not the first time scientists have proposed ancient relatives and early modern humans were intimately acquainted. In earlier research, researchers have discovered humans and their Neanderthal relatives shared the same mouth microbe for millions of years after the evolutionary divergence, suggesting they swapped saliva.

"Likely they were engaging in intimate contact," she said, adding that the idea chimed with research that has revealed people of non-African ancestry contain Neanderthal DNA in their genome, revealing genetic mixing was occurring.

Romantic Interpretation

"This offers a different spin on human-Neanderthal relations," Brindle said.

Publishing in the publication Evolution and Human Behavior, the researcher and her team report how, to explore the historical roots of intimate contact, they first had to come up with a description that was not limited to how humans kiss.

Defining Intimate Contact

"Previously there were some efforts to describe a intimate act, but it's very much been focused on humans, which implies that basically other animals do not engage in this. Now we understand that they probably do, it may appear different from what human kissing looks like," said the evolutionary biologist.

However, she noted some behaviors that resembled kissing were distinct activities – such as the processing and transfer of food, or "kiss-fighting", seen in aquatic species called certain marine animals.

Consequently the research group came up with a description of kissing centered around friendly interactions involving directed mouth-to-mouth contact with a member of the identical group, with some motion of the oral area but no transfer of nutrition.

Study Approach

Brindle said they focused on reports of intimate behavior in primates from Africa and Asia, including bonobos, chimpanzees and orangutans, and employed digital recordings to confirm the observations.

Scientists then combined this information with information on the evolutionary relationships between living and extinct species of such animals.

Evolutionary Timeline

Researchers say the findings indicate intimate contact evolved approximately 21.5m and 16.9 million years ago in the predecessors of the large apes.

Placement of Neanderthals on this evolutionary lineage means it is probable they, too, indulged in a intimate act, the researchers conclude. But the activity may not have been confined to their specific group.

"Reality that modern people engage intimately, the reality that we currently have demonstrated that ancient relatives very likely kissed, suggests that the both groups are probably did engage," Brindle noted.

Evolutionary Significance

Although the evolutionary explanation is debated, the expert said kissing could be employed in reproductive situations to potentially enhance reproductive success or help choose between mates, while it might help reinforce bonding when practiced in a non-sexual manner.

A separate researcher in the behavior of primates said that as intimate contact was observed in a wide range of apes it made sense its roots extend far into our ancient history, and an analysis of different forms of kissing among a wider variety of species might extend its beginnings back even earlier still.

"Things that we consider as signatures of human life, like kissing, are not unique to us if we examine carefully at other animals," the expert noted.

Cultural Aspects

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

"However, as people we thrive or fail on the quality of our relationships, and methods of promoting confidence and intimacy will have been significant for eons," the professor stated. "It might be an concept that seems a bit incongruous to our incorrect assumptions of a rather ruthless and aggressive past, but actually it should be no surprise that ancient hominins – and even them and our own species collectively – kissed."