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

Common Oral Evidence

It is not the first time scientists have suggested ancient relatives and early modern humans were closely connected. In earlier research, scientists have found modern people and their Neanderthal relatives possessed the same mouth microbe for hundreds of thousands of years after the two species split, implying they swapped saliva.

"Probably they were kissing," the researcher noted, adding that the idea chimed with research that has revealed humans of non-African ancestry contain ancient genetic material in their genome, demonstrating genetic mixing was occurring.

Romantic Interpretation

"This offers a more romantic spin on ancient interactions," Brindle said.

Publishing in the journal Evolution and Human Behavior, the researcher 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.

Describing Kissing

"There have been some previous attempts to define a kiss, but it's largely focused on humans, which implies that essentially other animals do not engage in this. Currently we understand that they likely engage, it might just not look from what human kissing looks like," said Brindle.

Nonetheless, she said some behaviors that resembled intimate contact were something rather different – such as the chewing and food sharing, or "mouth contact", observed in fish called certain marine animals.

Consequently the research group came up with a description of kissing based on friendly interactions involving directed oral interaction with a individual of the same species, with some motion of the oral area but absence of nutrition.

Research Approach

Brindle explained they concentrated on reports of intimate behavior in non-human species from the African continent and Asian regions, including primates, apes and orangutans, and used digital recordings to confirm the observations.

Scientists then combined this data with information on the genetic connections between extant and extinct species of such primates.

Evolutionary Origins

Researchers say the results indicate intimate contact developed approximately 21.5 million and 16.9m years ago in the predecessors of the great primates.

The position of Neanderthals on this evolutionary lineage means it is probable they, too, engaged in a kiss, the researchers say. But the activity might not have been limited to their own species.

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

Evolutionary Importance

Although the scientific reasoning is debated, Brindle said kissing could be used in sexual contexts to potentially increase reproductive success or assist in selecting between partners, while it could assist strengthen connections when used in a non-sexual manner.

Another expert in the behavior of great apes commented that as intimate contact was observed in a wide range of apes it made sense its origins extend far into our evolutionary past, and an examination of different forms of kissing among a wider variety of species might push its origins back even earlier still.

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

Cultural Elements

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

"Nonetheless, as people we thrive or fail 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 concept that seems a bit incongruous to our misplaced ideas of a supposedly aggressive and aggressive past, but really it should be expected that Neanderthals – and including them and our own species together – engaged intimately."