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Among Galápagos albatrosses to Arctic mammals, chimpanzees to great apes, 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

This isn't the initial instance experts have proposed Neanderthals and early modern humans were intimately acquainted. In earlier research, researchers have found modern people and their thick-browed cousins shared the identical oral bacteria for millions of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Likely they were engaging in intimate contact," she said, adding that the idea aligned with studies that has found humans of certain genetic backgrounds have bits of ancient genetic material in their genetic makeup, revealing interbreeding was occurring.

Romantic Interpretation

"It certainly puts a more romantic spin on ancient interactions," the lead researcher said.

Writing in the publication a scientific periodical, the researcher and her team report how, to investigate the evolutionary origins of intimate contact, they first had to come up with a definition that was not limited to how people smooch.

Describing Kissing

"There have been some efforts to describe a kiss, but it's largely focused on humans, which means that basically other animals do not engage in this. Now we understand that they probably do, it may appear different from what human kissing resembles," said Brindle.

However, she said some behaviors that looked like intimate contact were something rather different – such as the processing and transfer of food, or "kiss-fighting", observed in fish known as certain marine animals.

Consequently the research group came up with a description of kissing based on friendly interactions involving intentional mouth-to-mouth contact with a member of the identical group, with some motion of the mouth but no transfer of food.

Research Approach

The lead researcher explained they focused on reports of kissing in primates from Africa and Asia, including primates, apes and orangutans, and employed online videos to verify the reports.

Scientists then combined this information with details on the evolutionary relationships between extant and extinct species of such primates.

Evolutionary Timeline

Researchers say the results indicate intimate contact evolved approximately 21.5m and 16.9 million years ago in the predecessors of the great primates.

The position of ancient hominins on this family tree suggests it is probable they, too, indulged in a kiss, the scientists conclude. But the behavior might not have been limited to their specific group.

"Reality that humans engage intimately, the fact that we currently have shown that ancient relatives probably engaged, suggests that the both groups are also likely to have kissed," the researcher added.

Biological Importance

Although the evolutionary explanation is debated, the expert said kissing could be used in sexual contexts to possibly enhance mating outcomes or assist in selecting between partners, while it might help strengthen connections when practiced in a non-sexual manner.

Another expert in the behavior of great apes commented that as intimate contact was seen in a broad spectrum of apes it was logical its roots extend far into our ancient history, and an examination of various types of intimate behavior among a wider variety of species might push its beginnings back further still.

"Behaviors that we consider as signatures of our species, like kissing, are not unique to us if we examine carefully at different species," the expert noted.

Cultural Aspects

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

"Nonetheless, as people we succeed or struggle on the strength of our relationships, and methods of encouraging trust and closeness will have been important for eons," she said. "It might be an concept that appears a bit contradictory to our incorrect assumptions of a supposedly aggressive and ancient history, but actually it ought to be expected that Neanderthals – and even Neanderthals and our human ancestors together – kissed."