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From Galápagos albatrosses to Arctic mammals, primates to great apes, various animals appear to kiss. Now, scientists propose that Neanderthals also engaged in this behavior – 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 closely connected. Among earlier research, researchers have discovered humans and their thick-browed cousins 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 revealed humans of certain genetic backgrounds contain ancient genetic material in their genetic makeup, revealing genetic mixing was at play.

Romantic Interpretation

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

Writing in the publication a scientific periodical, Brindle and her team report how, to investigate the evolutionary origins of kissing, they first had to come up with a definition that was not restricted by how people smooch.

Defining Intimate Contact

"There have been some efforts to define a kiss, but it's very much been focused on humans, which means that essentially non-human species don't kiss. Now we know that they probably do, it may appear different from what our intimate contact resembles," said 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 fish known as certain marine animals.

Consequently the team developed a description of intimate contact centered around social behaviors involving directed mouth-to-mouth contact with a individual of the identical group, with some motion of the mouth but no transfer of nutrition.

Study Approach

Brindle said they concentrated on accounts of intimate behavior in primates from the African continent and Asia, including bonobos, chimpanzees and orangutans, and used digital recordings to verify the observations.

Scientists then integrated this information with information on the genetic connections between extant and extinct species of such primates.

Evolutionary Timeline

The team say the results suggest intimate contact developed approximately 21.5 million and 16.9 million years ago in the ancestors of the great primates.

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

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

Evolutionary Importance

Although the evolutionary explanation is debated, Brindle explained kissing could be used in reproductive situations to potentially increase reproductive success or assist in selecting between mates, while it might help strengthen connections when used in a platonic way.

A separate researcher in the activities of great apes commented that as intimate contact was seen in a wide range of apes it was logical its roots extend far into our ancient history, and an examination of different forms of intimate behavior among a wider variety of animals might push its beginnings back further still.

"Behaviors that we consider 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 kissing had a social component as it was not common to all societies.

"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," the professor stated. "This could represent an image that appears a bit incongruous to our incorrect assumptions of a rather ruthless and aggressive past, but actually it ought to be expected that Neanderthals – and including them and our own species together – kissed."