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From seabirds to polar bears, chimpanzees to great apes, various animals appear to kiss. Now, researchers suggest that Neanderthals also engaged in this behavior – and possibly exchanged kisses with early Homo sapiens.

Shared Microbial Evidence

It is not the first time scientists have suggested ancient relatives and Homo sapiens were closely connected. In earlier research, scientists have discovered modern people and their thick-browed cousins shared the same mouth microbe for millions of years after the two species split, suggesting they exchanged oral fluids.

"Probably they were engaging in intimate contact," she said, adding that the idea aligned with research that has found humans of non-African ancestry have bits of ancient genetic material in their genome, demonstrating interbreeding was at play.

Romantic Spin

"It certainly puts a different perspective on ancient interactions," the lead researcher said.

Writing in the publication a scientific periodical, the researcher and her team detail how, to explore the historical roots of intimate contact, they first had to develop a description that was not limited to how people smooch.

Defining Kissing

"There have been some efforts to describe a intimate act, but it's largely human-centric, which implies that basically other animals don't kiss. Currently we know that they probably do, it might just not look from what human kissing resembles," said the evolutionary biologist.

Nonetheless, she noted some actions that looked like intimate contact were distinct activities – such as the chewing and transfer of food, or "mouth contact", observed in fish called certain marine animals.

As a result the research group came up with a definition of kissing based on social behaviors involving intentional oral interaction with a individual of the same species, with some motion of the mouth but no transfer of food.

Research Methods

Brindle explained they focused on reports of kissing in non-human species from the African continent and Asia, including primates, apes and great apes, and used digital recordings to confirm the reports.

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

Evolutionary Origins

The team propose the results suggest intimate contact developed approximately 21.5 million and 16.9 million years ago in the predecessors of the large apes.

Placement of Neanderthals on this evolutionary lineage means it is probable they, too, engaged in a intimate act, the scientists say. But the behavior might not have been confined to their specific group.

"The fact that modern people engage intimately, the fact that we currently have demonstrated that Neanderthals very likely kissed, indicates that the both groups are also likely to have kissed," Brindle noted.

Evolutionary Significance

Although the scientific reasoning is discussed, Brindle explained intimate contact could be used in sexual contexts to possibly increase reproductive success or help choose between partners, while it might help reinforce bonding when practiced in a platonic way.

Another expert in the behavior of primates said that as intimate contact was seen in a broad spectrum of primates it made sense its origins lie deep in our ancient history, and an examination of various types of intimate behavior among a wider variety of species might extend its origins back further still.

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

Cultural Elements

Another professor explained that intimate contact had a social component as it was not common to all societies.

"Nonetheless, as humans we thrive or fail on the quality of our emotional bonds, and methods of encouraging trust and intimacy will have been significant for millions of years," she said. "It might be an image that appears a bit contradictory to our incorrect assumptions of a supposedly aggressive and aggressive past, but actually it ought to be expected that Neanderthals – and including Neanderthals and our own species together – kissed."