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From Galápagos albatrosses to polar bears, primates to great apes, certain species appear to kiss. Now, researchers propose that ancient hominins also engaged in this behavior – and might even have exchanged kisses with modern humans.

Shared Microbial Evidence

It is not the first time experts have suggested Neanderthals and early modern humans were closely connected. Among previous studies, researchers have found humans and their Neanderthal relatives possessed the same mouth microbe for hundreds of thousands of years after the two species split, suggesting they swapped saliva.

"Likely they were engaging in intimate contact," she said, adding that the concept chimed with research that has found people of non-African ancestry contain Neanderthal DNA in their genome, demonstrating interbreeding was occurring.

Intimate Spin

"It certainly puts a different spin on human-Neanderthal relations," the lead researcher commented.

Publishing in the journal a scientific periodical, Brindle and her team detail how, to investigate the historical roots of kissing, they first had to develop a description that was not limited to how humans smooch.

Defining Kissing

"There have been some efforts to define a kiss, but it's very much been human-centric, which means that essentially other animals don't kiss. Now we understand that they probably do, it might just not look from what our intimate contact resembles," said Brindle.

Nonetheless, she said some behaviors that looked like kissing were distinct activities – such as the processing and food sharing, or "mouth contact", observed in aquatic species known as French grunts.

Consequently the team developed a description of intimate contact centered around social behaviors involving directed oral interaction with a member of the same species, with some motion of the oral area but no transfer of nutrition.

Study Methods

Brindle said they concentrated on reports of intimate behavior in non-human species from Africa and Asian regions, including primates, apes and great apes, and used online videos to confirm the observations.

The researchers then combined this information with details on the evolutionary relationships between living and extinct types of such primates.

Evolutionary Origins

Researchers say the findings suggest kissing evolved 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 likely they, too, engaged in a intimate act, the researchers conclude. But the activity may not have been confined to their own species.

"The fact that humans engage intimately, the fact that we currently have shown that Neanderthals very likely engaged, indicates that the two [species] are probably did engage," the researcher noted.

Evolutionary Importance

While the scientific reasoning is debated, the expert said kissing could be used in sexual contexts to potentially enhance reproductive success or help choose between mates, while it could assist strengthen connections when used in a non-sexual manner.

Another expert in the activities of primates said that as intimate contact was seen in a broad spectrum of primates it made sense its roots extend far into our ancient history, and an analysis of various types of intimate behavior among a broader range of species might extend its beginnings back further still.

"Behaviors that we consider as signatures of our species, like kissing, are not unique to us if we examine carefully at different species," he said.

Cultural Aspects

An archaeology expert explained that kissing had a social component as it was not universal to all human groups.

"However, as humans we succeed or struggle on the quality of our relationships, and ways of encouraging trust and intimacy will have been significant for millions of years," the professor stated. "This could represent an concept that appears a bit contradictory to our incorrect assumptions of a supposedly aggressive and ancient history, but really it should be no surprise that Neanderthals – and including them and our own species collectively – engaged intimately."