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Among Galápagos albatrosses to Arctic mammals, primates to orangutans, certain species engage in mouth-to-mouth contact. Now, researchers suggest that Neanderthals did it too – and might even have exchanged kisses with early Homo sapiens.

Common Oral Clues

It is not the first time experts have suggested ancient relatives and Homo sapiens were intimately acquainted. In previous studies, scientists have found modern people and their Neanderthal relatives shared the identical oral bacteria for millions of years after the evolutionary divergence, suggesting they swapped saliva.

"Likely they were kissing," the researcher noted, explaining that the concept chimed with research that has found people of non-African ancestry have bits of ancient genetic material in their genetic makeup, demonstrating genetic mixing was occurring.

Intimate Interpretation

"It certainly puts a different spin on ancient interactions," Brindle said.

Writing in the journal Evolution and Human Behavior, the researcher and her team detail how, to investigate the historical roots of intimate contact, they first had to develop a definition that was not limited to how people kiss.

Describing Kissing

"There have been some previous attempts to define a kiss, but it's largely focused on humans, which implies that essentially non-human species do not engage in this. Currently we know that they probably do, it may appear different from what our intimate contact resembles," explained the evolutionary biologist.

Nonetheless, she said some actions that resembled kissing were something rather different – such as the chewing and transfer of food, or "mouth contact", observed in fish known as French grunts.

Consequently the team came up with a definition of kissing based on social behaviors involving directed mouth-to-mouth contact with a individual of the identical group, with some motion of the oral area but no transfer of nutrition.

Research Approach

Brindle said they focused on reports of kissing in non-human species from Africa and Asian regions, including bonobos, apes and great apes, and used digital recordings to confirm the observations.

The researchers then integrated this information with details on the genetic connections between extant and ancient species of such animals.

Historical Timeline

Researchers say the findings indicate kissing developed somewhere between 21.5m and 16.9 million years ago in the predecessors of the great primates.

The position of ancient hominins on this evolutionary lineage suggests it is likely they, too, indulged in a intimate act, the researchers say. But the behavior may not have been confined to their specific group.

"The fact that modern people kiss, the fact that we now have demonstrated that ancient relatives very likely kissed, suggests that the two [species] are also likely to have kissed," the researcher added.

Biological Importance

Although the scientific reasoning is debated, the expert explained kissing could be used in reproductive situations to potentially enhance reproductive success or assist in selecting between partners, while it might help strengthen connections when practiced in a platonic way.

A separate researcher in the activities of primates commented that as intimate contact was observed in a wide range of apes it made sense its origins extend far into our ancient history, and an examination of different forms of intimate behavior among a broader range of animals might extend its origins back further still.

"Behaviors that we think of as characteristics of our species, like intimate contact, are not exclusive to us if we examine carefully at different species," he said.

Social Elements

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

"Nonetheless, as humans we thrive or fail on the quality of our relationships, and methods of encouraging confidence and intimacy will have been important for millions of years," the professor stated. "It might be an image that seems a bit contradictory to our misplaced ideas of a supposedly aggressive and ancient history, but actually it should be expected that ancient hominins – and even Neanderthals and our human ancestors collectively – engaged intimately."