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Among Galápagos albatrosses to polar bears, primates to great apes, various animals appear to kiss. Now, scientists suggest that ancient hominins did it too – and possibly locked lips with early Homo sapiens.

Common Microbial Clues

This isn't the initial instance experts have proposed ancient relatives and early modern humans were intimately acquainted. Among earlier research, scientists have found modern people and their thick-browed cousins shared the same mouth microbe 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 aligned with research that has revealed people of non-African ancestry contain Neanderthal DNA in their genetic makeup, revealing genetic mixing was at play.

Romantic Spin

"This offers a different spin on human-Neanderthal relations," the lead researcher commented.

Writing in the journal Evolution and Human Behavior, the researcher and colleagues report how, to investigate the evolutionary origins of intimate contact, they first had to develop a definition that was not limited to how people kiss.

Describing Intimate Contact

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

Nonetheless, she said some actions that resembled kissing were distinct activities – such as the chewing and food sharing, or "mouth contact", seen in fish called French grunts.

As a result the research group came up with a description of intimate contact centered around friendly interactions involving directed mouth-to-mouth contact with a member of the same species, with some motion of the mouth but absence of food.

Research Approach

The lead researcher explained they focused on reports of kissing in non-human species from Africa and Asian regions, including bonobos, apes and orangutans, and employed online videos to verify the observations.

Scientists then combined this information with information on the evolutionary relationships between extant and ancient species of such primates.

Historical Origins

Researchers say the findings indicate kissing developed approximately 21.5m and 16.9m years ago in the ancestors of the great primates.

The position of Neanderthals on this evolutionary lineage means it is probable they, too, engaged in a kiss, the scientists say. But the activity might not have been limited to their specific group.

"Reality that modern people engage intimately, the reality that we currently 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 discussed, the expert said kissing could be employed in sexual contexts to possibly increase mating outcomes or assist in selecting between partners, while it might help reinforce bonding when used in a platonic way.

Another expert in the activities of primates commented that as intimate contact was observed in a broad spectrum of primates it was logical its origins lie deep in our evolutionary past, and an analysis of different forms of intimate behavior among a broader range of species might push its beginnings back further still.

"Things that we consider as characteristics of our species, like intimate contact, are not exclusive to us if we look closely at other animals," he said.

Social Elements

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

"However, as people we thrive or fail on the quality of our relationships, and methods of encouraging trust and intimacy will have been significant for millions of years," the professor stated. "This could represent an concept that appears a bit incongruous to our incorrect assumptions of a rather ruthless and ancient history, but actually it ought to be no surprise that Neanderthals – and including them and our human ancestors collectively – kissed."