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From Galápagos albatrosses to Arctic mammals, primates to great apes, various animals engage in mouth-to-mouth contact. Now, scientists propose that Neanderthals also engaged in this behavior – and possibly exchanged kisses with early Homo sapiens.

Shared Microbial Evidence

This isn't the initial instance experts have suggested ancient relatives and Homo sapiens were intimately acquainted. In previous studies, scientists have discovered modern people 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 engaging in intimate contact," the researcher noted, explaining that the idea chimed with studies that has revealed humans of certain genetic backgrounds have bits of Neanderthal DNA in their genome, revealing genetic mixing was occurring.

Romantic Interpretation

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

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

Defining Kissing

"There have been some previous attempts to define a intimate act, but it's very much been focused on humans, which implies that basically non-human species do not engage in this. Currently we know that they likely engage, it might just not look from what our intimate contact resembles," explained Brindle.

However, she said some actions that resembled intimate contact were something rather different – such as the processing and transfer of food, or "kiss-fighting", seen in aquatic species called certain marine animals.

Consequently the team developed a description of intimate contact centered around friendly interactions involving directed mouth-to-mouth contact with a individual of the same species, with some movement of the mouth but absence of nutrition.

Study Approach

Brindle said they concentrated on reports of intimate behavior in primates from Africa and Asia, including bonobos, chimpanzees and great apes, and used digital recordings to confirm the reports.

The researchers then integrated this data with information on the genetic connections between extant and ancient species of such primates.

Evolutionary Origins

Researchers propose the findings suggest kissing developed somewhere between 21.5m and 16.9m years ago in the predecessors of the large apes.

The position of Neanderthals on this family tree suggests it is likely they, too, engaged in a intimate act, the scientists say. But the behavior may not have been limited to their own species.

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

Evolutionary Importance

While the evolutionary explanation is debated, Brindle explained intimate contact could be employed in reproductive situations to potentially enhance mating outcomes or help choose between partners, while it might help reinforce bonding when practiced in a non-sexual manner.

A separate researcher in the behavior of great apes commented that as kissing behavior was seen in a wide range of primates it was logical its origins extend far into our ancient history, and an examination of various types of intimate behavior among a broader range of species might extend its beginnings back even earlier still.

"Things that we think of as signatures of our species, like kissing, are not unique to us if we look closely at other animals," the expert noted.

Social Elements

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

"Nonetheless, as people we succeed or struggle on the strength of our emotional bonds, and methods of encouraging confidence and intimacy will have been significant for eons," she said. "This could represent an image that appears a bit contradictory to our misplaced ideas of a supposedly aggressive and aggressive past, but actually it should be no surprise that ancient hominins – and even them and our own species together – kissed."