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From Galápagos albatrosses to polar bears, primates to orangutans, certain species appear to kiss. Now, researchers suggest that ancient hominins did it too – and might even have locked lips with modern humans.

Common Microbial Evidence

This isn't the initial instance scientists have suggested ancient relatives and Homo sapiens were closely connected. Among earlier research, researchers have found modern people and their thick-browed cousins shared the identical oral bacteria for millions of years after the evolutionary divergence, suggesting they swapped saliva.

"Probably they were kissing," the researcher noted, explaining that the concept chimed with studies that has found humans of certain genetic backgrounds have bits of ancient genetic material in their genetic makeup, revealing genetic mixing was occurring.

Intimate Spin

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

Writing in the publication a scientific periodical, the researcher and colleagues report how, to explore the evolutionary origins of kissing, they first had to develop a description that was not limited to how humans smooch.

Defining Intimate Contact

"There have been some efforts to define a intimate act, but it's very much been human-centric, which means that basically other animals do not engage in this. Now we understand that they probably do, it might just not look from what human kissing looks like," explained the evolutionary biologist.

Nonetheless, she noted some actions that looked like intimate contact were something rather different – such as the processing and transfer of food, or "mouth contact", observed in fish called French grunts.

Consequently the team developed a definition of intimate contact based on social behaviors involving intentional oral interaction with a individual of the same species, with some motion of the mouth but no transfer of food.

Study Methods

The lead researcher explained they focused on reports of intimate behavior in primates from Africa and Asian regions, including primates, apes and orangutans, and employed online videos to verify the observations.

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

Evolutionary Origins

The team propose the findings suggest intimate contact developed somewhere between 21.5m and 16.9m years ago in the ancestors of the large apes.

The position of Neanderthals on this family tree means it is probable they, too, engaged in a kiss, the researchers say. But the activity may not have been limited to their specific group.

"Reality that humans kiss, the reality that we currently have shown that ancient relatives very likely engaged, indicates that the both groups are probably did kissed," Brindle noted.

Biological Significance

While the evolutionary explanation is discussed, the expert said kissing could be employed in sexual contexts to potentially increase reproductive success or assist in selecting between partners, while it might help strengthen connections when practiced in a non-sexual manner.

A separate researcher in the behavior of great apes said that as kissing behavior was seen in a wide range of apes it was logical its origins lie deep in our ancient history, and an analysis of various types of kissing among a broader range of animals might extend its beginnings back even earlier still.

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

Cultural Aspects

Another professor explained that kissing had a social component as it was not common to all human groups.

"However, as people we thrive or fail on the strength of our relationships, and ways of promoting trust and closeness will have been significant for eons," the professor stated. "It might be an concept 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 including Neanderthals and our human ancestors together – kissed."