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From seabirds to Arctic mammals, chimpanzees to orangutans, various animals appear to kiss. Currently, researchers propose that Neanderthals did it too – and might even have exchanged kisses with early Homo sapiens.

Shared Microbial Clues

It is not the first time scientists have suggested ancient relatives and Homo sapiens were closely connected. Among previous studies, researchers have discovered modern people and their thick-browed cousins possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, suggesting they swapped saliva.

"Probably they were engaging in intimate contact," the researcher noted, explaining that the concept chimed with research that has found people of non-African ancestry contain ancient genetic material in their genetic makeup, revealing interbreeding was occurring.

Romantic Spin

"It certainly puts a more romantic spin on ancient interactions," the lead researcher said.

Writing in the publication a scientific periodical, Brindle and her team detail how, to investigate the historical roots of intimate contact, they first had to develop a description that was not restricted by how humans smooch.

Defining Kissing

"There have been some efforts to describe a intimate act, but it's largely focused on humans, which implies that essentially non-human species don't kiss. Currently we know that they probably do, it might just not look from what our intimate contact resembles," said Brindle.

Nonetheless, she said some actions that resembled kissing were distinct activities – such as the processing and food sharing, or "mouth contact", seen in aquatic species known as certain marine animals.

As a result the research group came up with a definition of intimate contact based on social behaviors involving intentional oral interaction with a individual of the identical group, with some movement of the mouth but no transfer of nutrition.

Research Methods

The lead researcher said they concentrated on reports of kissing in non-human species from Africa and Asian regions, including bonobos, apes and orangutans, and used digital recordings to confirm the observations.

Scientists then combined this information with information on the evolutionary relationships between living and ancient types of such animals.

Historical Timeline

Researchers propose the findings indicate intimate contact evolved approximately 21.5m and 16.9 million years ago in the predecessors of the large apes.

The position of Neanderthals on this evolutionary lineage suggests it is likely they, too, indulged in a intimate act, the scientists conclude. But the behavior might not have been confined to their specific group.

"Reality that humans kiss, the fact that we currently have demonstrated that Neanderthals very likely kissed, indicates that the two [species] are probably did engage," Brindle noted.

Evolutionary Significance

Although the evolutionary explanation is discussed, the expert explained intimate contact could be employed in sexual contexts to potentially enhance mating outcomes or assist in selecting between mates, while it could assist strengthen connections when practiced in a non-sexual manner.

Another expert in the activities of great apes commented that as kissing behavior was seen in a wide range of apes it was logical its roots extend far into our evolutionary past, and an analysis of different forms of intimate behavior among a broader range of animals might extend its beginnings back further still.

"Behaviors that we consider as characteristics of human life, like kissing, are not unique to us if we examine carefully at other animals," the expert noted.

Social Aspects

Another professor explained that kissing had a social component as it was not common to all societies.

"However, as humans we succeed or struggle on the quality of our emotional bonds, and methods of promoting trust and intimacy will have been significant for eons," she said. "This could represent an image that appears a bit incongruous to our misplaced ideas of a rather ruthless and ancient history, but really it ought to be expected that Neanderthals – and even Neanderthals and our own species collectively – engaged intimately."