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Among seabirds to polar bears, chimpanzees to orangutans, various animals appear to kiss. Now, researchers suggest that ancient hominins did it too – and might even have exchanged kisses with modern humans.

Shared Oral Evidence

This isn't the initial instance experts have proposed Neanderthals and Homo sapiens were closely connected. Among earlier research, researchers have discovered modern people and their thick-browed cousins shared the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, suggesting they swapped saliva.

"Likely they were engaging in intimate contact," she said, adding that the idea aligned with research that has found humans of non-African ancestry have bits of ancient genetic material in their genetic makeup, demonstrating genetic mixing was at play.

Romantic Interpretation

"This offers a more romantic spin on ancient interactions," the lead researcher commented.

Writing in the publication Evolution and Human Behavior, the researcher and colleagues detail how, to explore the historical roots of kissing, they first had to develop a definition that was not restricted by how people smooch.

Describing Intimate Contact

"There have been some previous attempts to define a intimate act, but it's largely human-centric, which implies that basically non-human species do not engage in this. Currently we know that they probably do, it may appear different from what our intimate contact resembles," said Brindle.

Nonetheless, she said some actions that resembled intimate contact were something rather different – such as the processing and food sharing, or "mouth contact", seen in aquatic species called French grunts.

Consequently the team came up with a description of intimate contact based on friendly interactions involving intentional mouth-to-mouth contact with a member of the identical group, with some movement of the oral area but absence of food.

Study Methods

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

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

Evolutionary Timeline

The team say the findings suggest intimate contact evolved approximately 21.5m and 16.9 million years ago in the predecessors 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 limited to their specific group.

"Reality that humans kiss, the fact that we currently have shown that Neanderthals probably engaged, suggests that the two [species] are also likely to have engage," Brindle noted.

Biological Importance

Although the scientific reasoning is discussed, Brindle said kissing could be used in sexual contexts to potentially increase mating outcomes or help choose between mates, while it might help reinforce bonding when practiced in a non-sexual manner.

Another expert in the activities of great apes commented that as kissing behavior was observed in a wide range of apes it was logical its roots lie deep in our ancient history, and an analysis of various types of intimate behavior among a broader range of species might extend its beginnings back even earlier still.

"Things that we think of as characteristics of our species, like kissing, are not exclusive to us if we look closely at different species," he said.

Social Aspects

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

"Nonetheless, as people we thrive or fail on the quality of our relationships, and ways of encouraging confidence and closeness will have been significant for eons," she said. "It might be an concept that appears a bit contradictory to our incorrect assumptions of a supposedly aggressive and aggressive past, but really it ought to be no surprise that Neanderthals – and including them and our own species together – kissed."