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From Galápagos albatrosses to polar bears, chimpanzees to great apes, certain species engage in mouth-to-mouth contact. Currently, scientists propose that Neanderthals also engaged in this behavior – and possibly locked lips with early Homo sapiens.

Shared Oral Clues

It is not the first time experts have suggested Neanderthals and early modern humans were intimately acquainted. Among previous studies, scientists have found modern people and their Neanderthal relatives possessed the identical oral bacteria for hundreds of thousands of years after the two species split, suggesting they exchanged oral fluids.

"Likely they were engaging in intimate contact," she said, explaining that the concept aligned with research that has found people of certain genetic backgrounds contain ancient genetic material in their genetic makeup, demonstrating interbreeding was occurring.

Romantic Spin

"This offers a more romantic spin on human-Neanderthal relations," Brindle commented.

Publishing in the journal Evolution and Human Behavior, the researcher and colleagues report how, to explore the historical roots of intimate contact, they first had to develop a definition that was not limited to how humans kiss.

Describing Intimate Contact

"Previously there were some efforts to define a intimate act, but it's very much been human-centric, which means that essentially non-human species don't kiss. Currently we know that they likely engage, it may appear different from what our intimate contact looks like," explained the evolutionary biologist.

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 known as French grunts.

Consequently the team came up with a description 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 absence of food.

Study Approach

The lead researcher explained they concentrated on accounts of intimate behavior in primates from Africa and Asian regions, including bonobos, chimpanzees and great apes, and used digital recordings to confirm the reports.

The researchers then combined this data with details on the genetic connections between extant and ancient types of such primates.

Evolutionary Origins

The team say the results suggest intimate contact developed somewhere between 21.5 million and 16.9 million years ago in the predecessors of the great primates.

Placement of ancient hominins on this evolutionary lineage means it is likely they, too, engaged in a kiss, the researchers say. But the behavior may not have been confined to their specific group.

"Reality that humans engage intimately, the reality that we now have demonstrated that Neanderthals probably engaged, suggests that the two [species] are also likely to have kissed," the researcher added.

Biological Importance

Although the scientific reasoning is discussed, Brindle explained kissing could be used in reproductive situations to potentially enhance reproductive success 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 commented that as intimate contact was observed in a broad spectrum of apes it was logical its origins lie deep in our ancient history, and an examination of various types of kissing among a broader range of species might extend its beginnings back further still.

"Things that we think of as signatures of human life, like intimate contact, are not unique to us if we examine carefully at different species," he said.

Social Elements

An archaeology expert said that intimate contact had a social component as it was not common to all societies.

"Nonetheless, as people we thrive or fail on the quality of our relationships, and ways of promoting trust and intimacy will have been significant for eons," she said. "It might be an concept that seems a bit incongruous to our incorrect assumptions of a supposedly aggressive and ancient history, but really it should be no surprise that Neanderthals – and including Neanderthals and our human ancestors together – engaged intimately."