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From Galápagos albatrosses to Arctic mammals, primates to great apes, certain species appear to kiss. Currently, scientists suggest that Neanderthals also engaged in this behavior – and possibly locked lips with modern humans.

Shared Microbial Clues

This isn't the initial instance experts have proposed ancient relatives and Homo sapiens were intimately acquainted. Among previous studies, scientists have discovered modern people and their thick-browed cousins possessed the same mouth microbe for millions of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Probably they were engaging in intimate contact," the researcher noted, explaining that the idea aligned with studies that has found people of non-African ancestry contain ancient genetic material in their genome, revealing interbreeding was occurring.

Intimate Interpretation

"This offers a more romantic spin on human-Neanderthal relations," Brindle commented.

Writing in the publication a scientific periodical, the researcher and her team detail how, to investigate the historical roots of intimate contact, they first had to come up with a definition that was not restricted by how people smooch.

Defining Intimate Contact

"There have been some efforts to define a kiss, but it's very much been focused on humans, which implies that essentially non-human species don't kiss. Currently we know that they likely engage, it may appear different from what our intimate contact resembles," said Brindle.

However, she noted some actions that looked like intimate contact were something rather different – such as the processing and transfer of food, or "kiss-fighting", observed in aquatic species called certain marine animals.

Consequently the research group came up with a definition of intimate contact centered around friendly interactions involving directed mouth-to-mouth contact with a individual of the identical group, with some movement of the mouth but absence of food.

Study Methods

Brindle said they concentrated on accounts of kissing in primates from the African continent and Asian regions, including primates, chimpanzees and great apes, and employed digital recordings to verify the reports.

Scientists then combined this information with information on the genetic connections between living and ancient species of such primates.

Historical Origins

The team say the findings suggest kissing developed somewhere between 21.5 million and 16.9 million years ago in the ancestors of the large apes.

The position of Neanderthals on this evolutionary lineage suggests it is likely they, too, indulged in a kiss, the scientists conclude. But the activity might not have been confined to their own species.

"Reality that humans engage intimately, the fact that we currently have demonstrated that ancient relatives very likely kissed, indicates that the both groups are also likely to have engage," the researcher noted.

Evolutionary Importance

While the evolutionary explanation is discussed, the expert explained kissing could be employed in reproductive situations to possibly increase mating outcomes or assist in selecting between mates, while it might help strengthen connections when used in a platonic way.

Another expert in the behavior of primates said that as kissing behavior was seen in a wide range of apes it was logical its origins extend far into our evolutionary past, and an analysis of various types of intimate behavior among a broader range of species might push its beginnings back even earlier still.

"Behaviors that we consider as signatures of our species, like intimate contact, are not unique to us if we look closely at other animals," the expert noted.

Cultural Elements

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

"However, as humans we succeed or struggle on the strength of our relationships, and methods of encouraging confidence and intimacy will have been significant for eons," the professor stated. "This could represent an image that seems a bit contradictory to our misplaced ideas of a rather ruthless and aggressive past, but really it ought to be expected that Neanderthals – and even Neanderthals and our own species together – engaged intimately."