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From Galápagos albatrosses to polar bears, primates to orangutans, various animals engage in mouth-to-mouth contact. Now, scientists propose that Neanderthals did it too – and might even have exchanged kisses with early Homo sapiens.

Common Microbial Clues

This isn't the initial instance experts have suggested ancient relatives and Homo sapiens were intimately acquainted. In previous studies, researchers have discovered modern people and their Neanderthal relatives possessed the identical oral bacteria for millions of years after the two species split, implying they exchanged oral fluids.

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

Intimate Interpretation

"It certainly puts a different spin on human-Neanderthal relations," the lead researcher said.

Publishing in the publication Evolution and Human Behavior, Brindle and colleagues report how, to explore the evolutionary origins of kissing, they first had to come up with a description that was not limited to how people kiss.

Defining Intimate Contact

"There have been some previous attempts to define a intimate act, but it's largely human-centric, which means that basically non-human species do not engage in this. Currently we know that they likely engage, it might just not look from what human kissing looks like," explained the evolutionary biologist.

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

Consequently the team developed a definition of intimate contact centered around social behaviors involving directed oral interaction with a individual of the same species, with some motion of the oral area but absence of food.

Study Methods

Brindle explained they focused on accounts of intimate behavior in primates from Africa and Asia, including bonobos, apes and great apes, and employed digital recordings to verify the reports.

The researchers then combined this information with information on the genetic connections between living and ancient species of such animals.

Historical Origins

Researchers say the findings indicate kissing evolved approximately 21.5 million and 16.9m years ago in the predecessors of the large apes.

Placement of ancient hominins on this evolutionary lineage means it is likely they, too, indulged in a kiss, the scientists say. But the behavior may not have been confined to their own species.

"Reality that humans kiss, the reality that we currently have demonstrated that Neanderthals very likely engaged, suggests that the both groups are probably did engage," Brindle noted.

Biological Importance

While the scientific reasoning is debated, the expert explained kissing could be employed in reproductive situations to possibly enhance mating outcomes 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 great apes said that as intimate contact was seen in a broad spectrum of primates it made sense its roots extend far into our evolutionary past, and an examination of various types of intimate behavior among a broader range of species might extend its origins back further still.

"Things that we think of as characteristics of human life, like kissing, are not unique to us if we look closely at other animals," the expert noted.

Social Aspects

Another professor explained that intimate contact had a cultural element as it was not common to all human groups.

"Nonetheless, as people we thrive or fail on the quality of our relationships, and ways of promoting confidence and closeness will have been significant for eons," she said. "This could represent an image that seems a bit contradictory to our incorrect assumptions of a rather ruthless and aggressive past, but really it should be expected that ancient hominins – and including them and our human ancestors together – kissed."