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Among Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, certain species appear to kiss. Now, scientists propose that ancient hominins also engaged in this behavior – and might even have locked lips with early Homo sapiens.

Common Microbial Evidence

This isn't the initial instance scientists have suggested ancient relatives and early modern humans were closely connected. Among earlier research, researchers have discovered modern people and their Neanderthal relatives shared the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, implying they swapped saliva.

"Likely they were engaging in intimate contact," the researcher noted, adding that the idea aligned with studies that has revealed humans of certain genetic backgrounds contain ancient genetic material in their genome, demonstrating interbreeding was occurring.

Romantic Spin

"It certainly puts a different perspective on ancient interactions," the lead researcher commented.

Publishing in the journal a scientific periodical, Brindle and her team detail how, to explore the historical roots of kissing, they first had to come up with a definition that was not limited to how humans kiss.

Defining Intimate Contact

"Previously there were some efforts to define a kiss, but it's very much been human-centric, which implies that essentially non-human species do not engage in this. Now we know that they probably do, it may appear different from what human kissing resembles," explained the evolutionary biologist.

However, she noted some actions that resembled kissing were distinct activities – such as the chewing and transfer of food, or "mouth contact", seen in aquatic species known as French grunts.

As a result the research group developed a definition of intimate contact based on friendly interactions involving directed mouth-to-mouth contact with a member of the same species, with some motion of the mouth but absence of nutrition.

Research Methods

Brindle said they focused on reports of intimate behavior in primates from the African continent and Asia, including primates, chimpanzees and orangutans, and used online videos to verify the reports.

Scientists then integrated this information with details on the evolutionary relationships between living and ancient species of such primates.

Historical Timeline

Researchers propose the results indicate intimate contact developed approximately 21.5 million and 16.9m years ago in the predecessors of the large apes.

Placement of Neanderthals on this evolutionary lineage means it is likely they, too, indulged in a intimate act, the researchers say. But the activity may not have been limited to their specific group.

"Reality that humans engage intimately, the reality that we now have shown that ancient relatives probably kissed, suggests that the both groups are also likely to have engage," the researcher added.

Biological Significance

Although the scientific reasoning is discussed, the expert explained intimate contact could be used in reproductive situations to potentially enhance mating outcomes or help choose between mates, while it could assist reinforce bonding when used in a non-sexual manner.

A separate researcher in the activities of great apes commented that as intimate contact was seen in a broad spectrum of primates it was logical its roots extend far into our ancient history, and an analysis of various types of intimate behavior among a broader range of animals might extend its beginnings back further still.

"Behaviors that we think of as characteristics of human life, like kissing, are not unique to us if we examine carefully at different species," 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 thrive or fail on the strength of our emotional bonds, and ways of promoting confidence and intimacy will have been important for millions of years," the professor stated. "This could represent an concept that appears a bit incongruous to our incorrect assumptions of a supposedly aggressive and aggressive past, but actually it ought to be no surprise that Neanderthals – and even Neanderthals and our human ancestors together – engaged intimately."