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From seabirds to polar bears, primates to great apes, certain species appear to kiss. Now, scientists suggest that Neanderthals also engaged in this behavior – and possibly locked lips with early Homo sapiens.

Shared Microbial Clues

It is not the first time scientists have proposed Neanderthals and Homo sapiens were intimately acquainted. Among earlier research, scientists have found modern people and their Neanderthal relatives shared the same mouth microbe for millions of years after the two species split, suggesting they swapped saliva.

"Probably they were engaging in intimate contact," the researcher noted, adding that the idea chimed with research that has found people of certain genetic backgrounds have bits of Neanderthal DNA in their genetic makeup, revealing interbreeding was at play.

Intimate Spin

"It certainly puts a more romantic spin on ancient interactions," the lead researcher said.

Publishing in the journal Evolution and Human Behavior, Brindle and colleagues detail how, to investigate the evolutionary origins of kissing, they first had to come up with a description that was not limited to how humans kiss.

Defining Intimate Contact

"There have been some previous attempts to describe a kiss, but it's largely focused on humans, which means that basically non-human species do not engage in this. Now we understand that they probably do, it might just not look from what our intimate contact resembles," explained Brindle.

Nonetheless, she said some actions that looked like intimate contact were distinct activities – such as the chewing and transfer of food, or "kiss-fighting", seen in fish known as certain marine animals.

As a result the research group developed a definition of intimate contact centered around friendly interactions involving directed mouth-to-mouth contact with a member of the same species, with some motion of the mouth but no transfer of food.

Research Approach

Brindle explained they concentrated on reports of kissing in primates from Africa and Asian regions, including bonobos, apes and orangutans, and used digital recordings to verify the observations.

Scientists then integrated this data with information on the genetic connections between extant and ancient types of such primates.

Historical Origins

The team propose the results suggest intimate contact developed somewhere between 21.5 million and 16.9m years ago in the predecessors of the large apes.

Placement of ancient hominins on this evolutionary lineage means it is likely they, too, indulged in a kiss, the scientists say. But the behavior might not have been confined to their own species.

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

Evolutionary Importance

While the evolutionary explanation is debated, Brindle explained kissing could be employed in reproductive situations to potentially increase reproductive success or help choose between mates, while it could assist strengthen connections when used in a platonic way.

Another expert in the behavior of primates commented that as kissing behavior was observed in a wide range of primates it made sense its roots lie deep in our evolutionary past, and an examination of various types of intimate behavior among a wider variety of animals might extend its beginnings back even earlier still.

"Behaviors that we think of as characteristics of our species, like kissing, are not unique to us if we examine carefully at different species," the expert noted.

Cultural Aspects

An archaeology expert explained that intimate contact had a cultural element as it was not universal to all societies.

"Nonetheless, as humans we thrive or fail on the quality of our emotional bonds, and methods of encouraging confidence and intimacy will have been significant for millions of years," the professor stated. "It might be an image that seems a bit incongruous to our incorrect assumptions of a supposedly aggressive and ancient history, but actually it ought to be expected that ancient hominins – and even them and our own species collectively – engaged intimately."