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From Galápagos albatrosses to Arctic mammals, primates to great apes, certain species engage in mouth-to-mouth contact. Now, researchers suggest that ancient hominins did it too – and might even have locked lips with early Homo sapiens.

Common Microbial Evidence

It is not the first time scientists have suggested ancient relatives and Homo sapiens were intimately acquainted. Among previous studies, scientists have found humans and their thick-browed cousins possessed the same mouth microbe for millions of years after the two species split, implying they exchanged oral fluids.

"Probably they were kissing," the researcher noted, explaining that the concept aligned with research that has revealed people of certain genetic backgrounds have bits of ancient genetic material in their genetic makeup, demonstrating interbreeding was at play.

Intimate Interpretation

"It certainly puts a different spin on ancient interactions," Brindle said.

Writing in the publication a scientific periodical, Brindle and colleagues detail how, to explore the evolutionary origins of kissing, they first had to come up with a description that was not limited to how humans smooch.

Describing Intimate Contact

"There have been some previous attempts to define a intimate act, but it's very much been focused on humans, which implies that basically non-human species do not engage in this. Now we understand that they likely engage, it may appear different from what human kissing looks like," said the evolutionary biologist.

Nonetheless, she noted some behaviors that looked like intimate contact were something rather different – such as the processing and food sharing, or "mouth contact", observed in aquatic species called certain marine animals.

Consequently the team came up with a description of kissing based on social behaviors involving intentional oral interaction with a member of the identical group, with some motion of the mouth but absence of nutrition.

Study Approach

The lead researcher explained they concentrated on accounts of intimate behavior in primates from Africa and Asian regions, including primates, apes and great apes, and employed online videos to confirm the observations.

Scientists then integrated this data with information on the genetic connections between extant and extinct species of such primates.

Historical Origins

The team propose the results indicate intimate contact developed approximately 21.5 million and 16.9 million years ago in the predecessors of the great primates.

Placement of ancient hominins on this evolutionary lineage suggests it is likely they, too, indulged in a kiss, the researchers conclude. But the behavior might not have been confined to their own species.

"The fact that humans engage intimately, the fact that we currently have demonstrated that Neanderthals probably engaged, suggests that the both groups are also likely to have kissed," Brindle noted.

Biological Importance

Although the evolutionary explanation is discussed, the expert said intimate contact could be used in sexual contexts to possibly increase reproductive success or assist in selecting between mates, while it might help reinforce bonding when practiced in a platonic way.

Another expert in the activities of great apes commented that as kissing behavior was seen in a wide range of apes it was logical its roots lie deep in our evolutionary past, and an examination of different forms of intimate behavior among a broader range of species might extend its beginnings back further still.

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

Cultural Aspects

Another professor said that kissing had a cultural element as it was not universal to all human groups.

"Nonetheless, as people we succeed or struggle on the strength of our relationships, and ways of encouraging trust and intimacy will have been important for eons," she said. "It might be an image that appears a bit contradictory to our misplaced ideas of a rather ruthless and ancient history, but really it ought to be no surprise that ancient hominins – and even them and our human ancestors together – engaged intimately."