🔗 Share this article

From Galápagos albatrosses to polar bears, primates to orangutans, certain species engage in mouth-to-mouth contact. Currently, scientists propose that ancient hominins did it too – and might even have locked lips with modern humans.

Shared Oral Evidence

It is not the first time experts have suggested Neanderthals and early modern humans were closely connected. In previous studies, researchers have found modern people and their Neanderthal relatives possessed the same mouth microbe for millions of years after the evolutionary divergence, suggesting they swapped saliva.

"Probably they were engaging in intimate contact," she said, adding that the idea chimed with research that has found people of non-African ancestry contain ancient genetic material in their genome, revealing interbreeding was at play.

Romantic Interpretation

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

Publishing in the publication Evolution and Human Behavior, Brindle and colleagues detail how, to investigate the evolutionary origins of kissing, they first had to come up with a definition that was not limited to how humans smooch.

Defining Kissing

"Previously there were some efforts to describe a kiss, but it's very much been focused on humans, which means that essentially other animals do not engage in this. Now we know that they likely engage, it may appear different from what human kissing resembles," said Brindle.

Nonetheless, she said some actions that resembled kissing were something rather different – such as the chewing and transfer of food, or "mouth contact", seen in fish known as French grunts.

As a result the research group came up with a definition of kissing centered around social behaviors involving directed oral interaction with a individual of the same species, with some movement of the oral area but absence of nutrition.

Study Methods

The lead researcher said they concentrated on accounts of kissing in non-human species from the African continent and Asia, including primates, chimpanzees and orangutans, and employed online videos to verify the observations.

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

Historical Origins

Researchers propose the findings indicate intimate contact evolved somewhere between 21.5 million and 16.9 million years ago in the predecessors of the great primates.

Placement of ancient hominins on this family tree means it is likely they, too, indulged in a kiss, the scientists conclude. But the behavior may not have been limited to their specific group.

"The fact that humans engage intimately, the fact that we currently have demonstrated that ancient relatives probably kissed, indicates that the two [species] are probably did engage," the researcher noted.

Evolutionary Importance

Although the scientific reasoning is discussed, the expert explained intimate contact could be used in sexual contexts to potentially enhance reproductive success or assist in selecting between partners, while it might help strengthen connections when used in a non-sexual manner.

Another expert in the behavior of great apes commented that as kissing behavior was observed in a broad spectrum of primates it was logical its origins 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 even earlier still.

"Things that we think of as characteristics of our species, like intimate contact, are not exclusive to us if we examine carefully at other animals," he said.

Social Aspects

Another professor said that kissing had a cultural element as it was not universal to all societies.

"Nonetheless, as people we succeed or struggle on the strength of our relationships, and ways of promoting confidence and intimacy will have been significant for millions of years," the professor stated. "This could represent an concept that appears a bit incongruous to our incorrect assumptions of a supposedly aggressive and aggressive past, but really it ought to be expected that Neanderthals – and including them and our own species collectively – kissed."