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From seabirds to polar bears, primates to orangutans, various animals appear to kiss. Now, researchers suggest that Neanderthals did it too – and possibly exchanged kisses with early Homo sapiens.

Shared Oral Clues

This isn't the initial instance scientists have proposed Neanderthals and early modern humans were closely connected. Among previous studies, researchers have discovered modern people and their thick-browed cousins possessed the identical oral bacteria for millions of years after the evolutionary divergence, implying they exchanged oral fluids.

"Likely they were engaging in intimate contact," the researcher noted, adding that the concept aligned with research that has found people of certain genetic backgrounds contain Neanderthal DNA in their genetic makeup, revealing genetic mixing was at play.

Intimate Spin

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

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

Describing Intimate Contact

"There have been some efforts to define a kiss, but it's very much been focused on humans, which implies that basically other animals do not engage in this. Now we understand that they likely engage, it might just not look from what our intimate contact looks like," said the evolutionary biologist.

Nonetheless, she noted some actions that resembled intimate contact were something rather different – such as the chewing and food sharing, or "mouth contact", observed in fish called French grunts.

Consequently the research group developed a description of kissing based on friendly interactions involving intentional oral interaction with a individual of the identical group, with some motion of the oral area but absence of nutrition.

Study Methods

Brindle explained they focused on accounts of kissing in primates from Africa and Asian regions, including primates, apes and great apes, and employed online videos to verify the reports.

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

Historical Timeline

The team propose the findings indicate kissing evolved 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 likely they, too, indulged in a kiss, the researchers say. But the activity may not have been limited to their own species.

"The fact that humans engage intimately, the fact that we currently have demonstrated that Neanderthals very likely kissed, suggests that the both groups are also likely to have engage," Brindle added.

Evolutionary Significance

Although the scientific reasoning is debated, Brindle said intimate contact could be used in reproductive situations to potentially increase mating outcomes or help choose between mates, while it might help reinforce bonding when used in a non-sexual manner.

A separate researcher in the behavior of primates commented that as intimate contact was observed in a wide range of apes it was logical its roots lie deep in our ancient history, and an examination of various types of kissing among a wider variety of species might extend its beginnings back further still.

"Things that we consider as signatures of human life, like kissing, are not exclusive to us if we examine carefully at other animals," he said.

Social Elements

Another professor explained that intimate contact had a cultural element as it was not universal to all human groups.

"Nonetheless, as humans we succeed or struggle on the quality of our relationships, and methods of promoting confidence and closeness will have been significant for eons," she said. "It might be an concept that seems a bit incongruous to our misplaced ideas of a supposedly aggressive and ancient history, but actually it ought to be expected that Neanderthals – and including them and our human ancestors collectively – engaged intimately."