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From seabirds to polar bears, chimpanzees to orangutans, various animals appear to kiss. Currently, researchers propose that Neanderthals did it too – and possibly exchanged kisses with modern humans.

Common Microbial Clues

It is not the first time experts have proposed Neanderthals and Homo sapiens were intimately acquainted. Among previous studies, researchers have found modern people and their Neanderthal relatives shared the identical oral bacteria for hundreds of thousands of years after the two species split, suggesting they swapped saliva.

"Probably they were engaging in intimate contact," the researcher noted, explaining that the concept aligned with research that has revealed people of certain genetic backgrounds have bits of ancient genetic material in their genetic makeup, demonstrating genetic mixing was occurring.

Intimate Interpretation

"It certainly puts a different spin on human-Neanderthal relations," Brindle commented.

Writing in the journal a scientific periodical, the researcher and colleagues detail how, to investigate the evolutionary origins of kissing, they first had to develop a description that was not restricted by how humans smooch.

Defining Kissing

"There have been some efforts to describe a intimate act, but it's largely human-centric, which means that basically non-human species do not engage in this. Currently we understand that they probably do, it might just not look from what our intimate contact resembles," said Brindle.

However, she noted some actions that looked like intimate contact were distinct activities – such as the processing and transfer of food, or "mouth contact", seen in fish known as certain marine animals.

As a result the research group developed a description of kissing centered around social behaviors involving directed mouth-to-mouth contact with a member of the identical group, with some motion of the mouth but no transfer of nutrition.

Study Methods

Brindle explained they concentrated on accounts of kissing in non-human species from Africa and Asian regions, including primates, chimpanzees and orangutans, and used digital recordings to confirm the reports.

Scientists then combined this information with details on the evolutionary relationships between living and ancient species of such animals.

Historical Origins

The team propose the findings suggest kissing evolved somewhere between 21.5 million and 16.9 million years ago in the ancestors of the large apes.

Placement of ancient hominins on this family tree suggests it is likely they, too, engaged in a intimate act, the scientists say. But the activity might not have been confined to their specific group.

"The fact that humans kiss, the reality that we currently have shown that ancient relatives very likely kissed, indicates that the two [species] are also likely to have engage," the researcher noted.

Evolutionary Importance

While the evolutionary explanation is discussed, the expert explained kissing could be employed in reproductive situations to possibly increase reproductive success or assist in selecting between partners, while it could assist strengthen connections when used in a non-sexual manner.

Another expert in the behavior of great apes commented that as intimate contact was seen in a wide range of apes it was logical its roots lie deep in our ancient history, and an analysis of various types of intimate behavior among a wider variety of animals might push its beginnings back further still.

"Things that we think of as signatures of human life, like kissing, are not exclusive to us if we examine carefully at different species," he said.

Social Aspects

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

"Nonetheless, as people we thrive or fail on the strength of our relationships, and methods of encouraging confidence and intimacy will have been significant for millions of years," the professor stated. "It might be an image that appears a bit incongruous to our misplaced ideas of a supposedly aggressive and aggressive past, but actually it should be no surprise that ancient hominins – and including them and our own species collectively – kissed."