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Among seabirds to polar bears, primates to great apes, various animals appear to kiss. Currently, researchers suggest that Neanderthals also engaged in this behavior – and possibly locked lips with modern humans.

Shared Oral Evidence

This isn't the initial instance scientists have proposed Neanderthals and Homo sapiens were closely connected. In previous studies, scientists have discovered humans and their Neanderthal relatives shared the same mouth microbe for hundreds of thousands of years after the two species split, implying they exchanged oral fluids.

"Probably they were engaging in intimate contact," she said, explaining that the idea chimed with research that has found people of certain genetic backgrounds contain ancient genetic material in their genome, revealing interbreeding was at play.

Intimate Spin

"It certainly puts a different perspective on ancient interactions," the lead researcher commented.

Writing in the journal a scientific periodical, Brindle and her team detail how, to explore the evolutionary origins of kissing, they first had to develop a description that was not limited to how people smooch.

Describing Intimate Contact

"There have been some efforts to define a kiss, but it's very much been focused on humans, which means that basically non-human species do not engage in this. Now we know that they likely engage, it may appear different from what human kissing resembles," said Brindle.

However, she noted some behaviors that looked like kissing were something rather different – such as the processing and food sharing, or "mouth contact", seen in aquatic species called certain marine animals.

As a result the research group came up with a definition of kissing centered around social behaviors involving directed oral interaction with a individual of the same species, with some motion of the mouth but absence of nutrition.

Research Approach

The lead researcher said they focused on reports of kissing in primates from the African continent and Asian regions, including primates, apes and great apes, and employed digital recordings to confirm the reports.

The researchers then integrated this information with information on the evolutionary relationships between extant and ancient species of such animals.

Evolutionary Timeline

The team propose the results indicate intimate contact developed somewhere between 21.5 million and 16.9m years ago in the ancestors of the great primates.

The position of ancient hominins on this family tree suggests it is probable they, too, indulged in a intimate act, the scientists conclude. But the behavior might not have been confined to their own species.

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

Evolutionary Significance

Although the evolutionary explanation is discussed, the expert explained kissing could be used in reproductive situations to potentially enhance reproductive success or assist in selecting between mates, while it could assist reinforce bonding when used in a non-sexual manner.

A separate researcher in the activities of primates commented that as kissing behavior was seen in a wide range of apes it was logical its roots extend far into our ancient history, and an analysis of different forms of intimate behavior among a wider variety of species might extend its beginnings back even earlier still.

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

Social Aspects

An archaeology expert said that kissing had a cultural element as it was not common to all human groups.

"Nonetheless, as humans we succeed or struggle on the strength of our emotional bonds, and methods of encouraging confidence and closeness will have been significant for millions of years," she said. "It might be an concept that appears a bit incongruous to our misplaced ideas of a supposedly aggressive and aggressive past, but really it ought to be no surprise that Neanderthals – and even them and our own species collectively – kissed."