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From Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, various animals appear to kiss. Currently, scientists suggest that ancient hominins did it too – and possibly locked lips with early Homo sapiens.

Common Microbial Evidence

This isn't the initial instance experts have proposed Neanderthals and Homo sapiens were intimately acquainted. Among previous studies, researchers have found humans and their thick-browed cousins possessed the identical oral bacteria for millions of years after the two species split, suggesting they swapped saliva.

"Likely they were engaging in intimate contact," the researcher noted, explaining that the concept chimed with research that has revealed people of non-African ancestry have bits of ancient genetic material in their genetic makeup, revealing genetic mixing was at play.

Romantic Spin

"This offers a different perspective on ancient interactions," Brindle said.

Publishing in the journal a scientific periodical, Brindle and colleagues detail how, to investigate the historical roots of intimate contact, they first had to come up with a description that was not restricted by how humans smooch.

Describing Intimate Contact

"Previously there were some previous attempts to define a kiss, but it's largely focused on humans, which means that essentially other animals do not engage in this. Currently we know that they likely engage, it may appear different from what our intimate contact resembles," said the evolutionary biologist.

Nonetheless, she noted some behaviors that resembled kissing were something rather different – such as the chewing and food sharing, or "kiss-fighting", seen in fish known as French grunts.

Consequently the team developed a definition of kissing based on social behaviors involving directed oral interaction with a member of the same species, with some movement of the mouth but absence of food.

Research Approach

The lead researcher said they focused on reports of kissing in non-human species from Africa and Asia, including bonobos, chimpanzees and great apes, and used digital recordings to verify the observations.

The researchers then integrated this information with details on the genetic connections between living and extinct types of such animals.

Evolutionary Timeline

Researchers propose the findings suggest intimate contact developed approximately 21.5m and 16.9 million years ago in the ancestors of the great primates.

Placement of ancient hominins on this family tree suggests it is likely they, too, engaged in a intimate act, the scientists conclude. But the activity might not have been limited to their specific group.

"Reality that modern people kiss, the reality that we now have demonstrated that ancient relatives very likely kissed, suggests that the two [species] are also likely to have kissed," the researcher added.

Biological Importance

While the scientific reasoning is debated, the expert said kissing could be employed in reproductive situations to possibly enhance mating outcomes or help choose between mates, while it might help strengthen connections when practiced in a platonic way.

Another expert in the activities of great apes said that as intimate contact was observed in a wide range of apes it was logical its roots lie deep in our evolutionary past, and an examination of different forms of kissing among a wider variety of species might push its origins back even earlier still.

"Behaviors that we consider as characteristics of human life, like intimate contact, are not unique to us if we look closely at other animals," he said.

Cultural Elements

Another professor explained that intimate contact had a social component as it was not universal to all societies.

"Nonetheless, as people we succeed or struggle on the quality of our relationships, and ways of encouraging trust and intimacy will have been important for millions of years," the professor stated. "This could represent an image that seems a bit incongruous to our incorrect assumptions of a rather ruthless and ancient history, but actually it ought to be expected that Neanderthals – and even Neanderthals and our own species collectively – kissed."