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Among Galápagos albatrosses to Arctic mammals, primates to orangutans, certain species engage in mouth-to-mouth contact. Now, scientists propose that ancient hominins did it too – and might even have exchanged kisses with early Homo sapiens.

Shared Microbial Evidence

This isn't the initial instance experts have proposed Neanderthals and Homo sapiens were intimately acquainted. Among previous studies, researchers have found modern people and their Neanderthal relatives possessed the identical oral bacteria for hundreds of thousands of years after the two species split, implying they swapped saliva.

"Probably they were engaging in intimate contact," the researcher noted, explaining that the concept chimed with research that has found humans of non-African ancestry contain ancient genetic material in their genetic makeup, revealing interbreeding was at play.

Romantic Interpretation

"It certainly puts a different perspective on human-Neanderthal relations," Brindle 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 people kiss.

Describing Intimate Contact

"There have been some previous attempts to define a intimate act, but it's very much been focused on humans, which means that essentially non-human species don't kiss. Now we understand that they probably do, it might just not look from what human kissing resembles," said the evolutionary biologist.

Nonetheless, she said some behaviors that resembled kissing were distinct activities – such as the processing and transfer of food, or "kiss-fighting", seen in fish called certain marine animals.

Consequently the team developed a description of kissing centered around friendly interactions involving intentional mouth-to-mouth contact with a member of the same species, with some motion of the oral area but absence of nutrition.

Research Methods

Brindle said they concentrated on reports of intimate behavior in primates from Africa and Asia, including bonobos, apes and orangutans, and used online videos to verify the reports.

The researchers then combined this data with information on the evolutionary relationships between living and ancient species of such animals.

Evolutionary Origins

The team say the findings indicate intimate contact developed somewhere between 21.5m and 16.9m years ago in the predecessors of the large apes.

Placement of Neanderthals on this evolutionary lineage means it is probable they, too, engaged in a intimate act, the researchers conclude. But the behavior may not have been limited to their own species.

"Reality that humans kiss, the reality that we currently have demonstrated that Neanderthals very likely kissed, indicates that the two [species] are probably did engage," the researcher noted.

Evolutionary Significance

While the scientific reasoning is discussed, Brindle explained intimate contact could be used in sexual contexts to possibly enhance reproductive success or assist in selecting between partners, while it might help strengthen connections when used in a non-sexual manner.

A separate researcher in the activities of primates said that as intimate contact was observed in a broad spectrum of primates it made sense its roots lie deep in our ancient history, and an examination of various types of intimate behavior among a broader range of species might push its beginnings back further still.

"Things that we think of as characteristics of our species, like kissing, are not exclusive to us if we examine carefully at different species," the expert noted.

Social Aspects

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

"Nonetheless, as humans we thrive or fail on the quality of our emotional bonds, and methods of promoting confidence and intimacy will have been significant for millions of years," the professor stated. "This could represent an concept that appears a bit contradictory to our misplaced ideas of a supposedly aggressive and aggressive past, but really it should be expected that ancient hominins – and including them and our own species together – engaged intimately."