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From seabirds to Arctic mammals, chimpanzees to orangutans, certain species engage in mouth-to-mouth contact. Now, researchers suggest that Neanderthals did it too – and might even have exchanged kisses with modern humans.

Common Microbial Evidence

It is not the first time scientists have proposed ancient relatives and early modern humans were closely connected. In earlier research, researchers have discovered modern people and their thick-browed cousins shared the same mouth microbe for millions of years after the two species split, suggesting they exchanged oral fluids.

"Likely they were engaging in intimate contact," she said, adding that the idea aligned with research that has revealed people of non-African ancestry have bits of Neanderthal DNA in their genetic makeup, revealing interbreeding was at play.

Romantic Spin

"This offers a different perspective on ancient interactions," Brindle said.

Writing in the publication a scientific periodical, the researcher and colleagues detail how, to investigate the historical roots of kissing, they first had to develop a definition that was not restricted by how humans kiss.

Defining Kissing

"Previously there were some previous attempts to define a intimate act, but it's largely human-centric, which implies that essentially non-human species don't kiss. Now we know that they probably do, it may appear different from what human kissing resembles," said Brindle.

Nonetheless, she noted some behaviors that looked like intimate contact were distinct activities – such as the processing and transfer of food, or "kiss-fighting", observed in aquatic species known as certain marine animals.

Consequently the team developed a definition of intimate contact centered around friendly interactions involving intentional mouth-to-mouth contact with a member of the same species, with some movement of the oral area but absence of food.

Research Methods

Brindle said they concentrated on reports of intimate behavior in primates from the African continent and Asian regions, including primates, chimpanzees and great apes, and used digital recordings to confirm the observations.

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

Evolutionary Timeline

Researchers say the results suggest intimate contact developed somewhere between 21.5m and 16.9 million years ago in the predecessors of the great primates.

Placement of Neanderthals on this family tree suggests it is likely they, too, engaged in a intimate act, the researchers conclude. But the activity may not have been confined to their specific group.

"The fact that modern people kiss, the fact that we currently have demonstrated that Neanderthals very likely engaged, indicates that the two [species] are also likely to have engage," the researcher noted.

Biological Importance

While the scientific reasoning is discussed, Brindle explained kissing could be used in sexual contexts to possibly increase reproductive success or help choose between partners, while it could assist strengthen connections when practiced in a non-sexual manner.

Another expert in the activities of great apes commented that as kissing behavior was seen in a broad spectrum of primates it made sense its origins extend far into our ancient history, and an examination of various types of intimate behavior among a broader range of animals might push its origins back even earlier still.

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

Social Elements

An archaeology expert said that intimate contact had a social component as it was not universal to all societies.

"Nonetheless, as humans we succeed or struggle on the quality of our relationships, and ways of promoting trust and closeness will have been significant for millions of years," the professor stated. "This could represent an concept that appears a bit contradictory to our incorrect assumptions of a rather ruthless and aggressive past, but actually it ought to be expected that Neanderthals – and even them and our own species together – engaged intimately."