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From Galápagos albatrosses to polar bears, chimpanzees to great apes, various animals appear to kiss. Currently, researchers suggest that ancient hominins also engaged in this behavior – and possibly locked lips with early Homo sapiens.

Common Oral Clues

This isn't the initial instance experts have suggested Neanderthals and Homo sapiens were intimately acquainted. In earlier research, researchers have discovered humans and their thick-browed cousins shared the same mouth microbe for millions of years after the evolutionary divergence, suggesting they swapped saliva.

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

Romantic Spin

"This offers a more romantic spin on ancient interactions," Brindle said.

Publishing in the publication a scientific periodical, the researcher and her team report how, to explore the historical roots of intimate contact, they first had to come up with a definition that was not limited to how humans kiss.

Describing Kissing

"There have been some previous attempts to define a kiss, but it's very much been focused on humans, which implies that basically other animals do not engage in this. Now we know that they probably do, it may appear different from what human kissing resembles," said Brindle.

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 certain marine animals.

As a result the research group developed a description of intimate contact centered around social behaviors involving intentional oral interaction with a member of the same species, with some movement of the mouth but absence of nutrition.

Study Methods

Brindle explained they concentrated on reports of intimate behavior in primates from the African continent and Asia, including bonobos, chimpanzees and orangutans, and employed digital recordings to verify the reports.

Scientists then integrated this data with information on the evolutionary relationships between extant and ancient species of such animals.

Historical Origins

Researchers say the findings indicate intimate contact developed somewhere between 21.5m and 16.9 million years ago in the ancestors of the large apes.

The position of Neanderthals on this evolutionary lineage means it is probable they, too, engaged in a kiss, the researchers conclude. But the activity might not have been confined to their own species.

"The fact that modern people kiss, the reality that we now have demonstrated that ancient relatives probably kissed, suggests that the two [species] are also likely to have kissed," the researcher added.

Evolutionary Significance

While the evolutionary explanation is debated, Brindle said kissing could be used in reproductive situations to possibly increase mating outcomes or help choose between mates, while it could assist reinforce bonding when practiced in a non-sexual manner.

A separate researcher in the activities of primates said that as intimate contact was observed in a wide range of primates it made sense its origins lie deep in our evolutionary past, and an analysis of various types of kissing among a broader range of animals might push its origins back further still.

"Things that we think of as signatures of our species, like intimate contact, are not unique to us if we examine carefully at different species," the expert noted.

Cultural Aspects

An archaeology expert explained that intimate contact had a cultural element as it was not universal to all human groups.

"Nonetheless, as humans we succeed or struggle on the quality of our emotional bonds, and ways of promoting trust and intimacy will have been important for eons," the professor stated. "This could represent an concept that seems a bit contradictory to our misplaced ideas of a rather ruthless and ancient history, but really it should be expected that Neanderthals – and even them and our human ancestors collectively – kissed."