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From Galápagos albatrosses to polar bears, chimpanzees to great apes, various animals appear to kiss. Now, scientists suggest that Neanderthals also engaged in this behavior – and possibly locked lips with modern humans.

Shared Microbial Evidence

This isn't the initial instance experts have proposed ancient relatives and Homo sapiens were closely connected. Among previous studies, scientists have discovered modern people and their Neanderthal relatives possessed the identical oral bacteria for millions of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Probably they were kissing," 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 genome, demonstrating genetic mixing was occurring.

Intimate Interpretation

"This offers a more romantic perspective on ancient interactions," Brindle commented.

Writing in the journal Evolution and Human Behavior, Brindle and colleagues detail how, to explore the evolutionary origins of intimate contact, they first had to develop a description that was not limited to how humans smooch.

Describing Intimate Contact

"There have been some previous attempts to define a intimate act, but it's largely focused on humans, which means that basically non-human species do not engage in this. Currently we understand that they probably do, it may appear different from what our intimate contact resembles," said the evolutionary biologist.

However, she said some behaviors that resembled kissing were something rather different – such as the processing and food sharing, or "mouth contact", seen in aquatic species known as French grunts.

Consequently the team developed a definition of kissing centered around friendly interactions involving directed mouth-to-mouth contact with a member of the identical group, with some movement of the oral area but absence of nutrition.

Study Approach

Brindle said they concentrated on accounts of intimate behavior in non-human species from Africa and Asia, including bonobos, chimpanzees and orangutans, and used online videos to confirm the observations.

Scientists then integrated this data with details on the evolutionary relationships between living and ancient types of such animals.

Historical Origins

Researchers propose the findings indicate kissing evolved approximately 21.5m and 16.9 million years ago in the predecessors of the great primates.

The position of Neanderthals on this evolutionary lineage suggests it is probable they, too, indulged in a intimate act, the scientists say. But the activity may not have been confined to their own species.

"Reality that humans engage intimately, the reality that we currently have shown that ancient relatives probably engaged, indicates that the both groups are probably did engage," Brindle added.

Evolutionary Importance

While the evolutionary explanation is debated, Brindle explained intimate contact could be employed in sexual contexts to possibly increase mating outcomes or assist in selecting between mates, while it might help strengthen connections when practiced in a non-sexual manner.

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

"Things that we think of as signatures of our species, like intimate contact, are not unique to us if we look closely at other animals," the expert noted.

Social Elements

Another professor said that kissing had a cultural element as it was not universal to all societies.

"However, as humans we succeed or struggle on the quality of our emotional bonds, and methods of encouraging trust and intimacy will have been important for millions of years," she said. "It might be an image that seems a bit incongruous to our misplaced ideas of a rather ruthless and ancient history, but really it should be expected that Neanderthals – and even Neanderthals and our own species together – engaged intimately."