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From Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, certain species engage in mouth-to-mouth contact. Currently, scientists suggest that ancient hominins did it too – and might even have exchanged kisses with early Homo sapiens.

Shared Oral Evidence

This isn't the initial instance experts have suggested ancient relatives and Homo sapiens were closely connected. Among earlier research, scientists have discovered modern people and their thick-browed cousins shared the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Likely they were engaging in intimate contact," she said, explaining that the idea chimed with research that has found people of non-African ancestry have bits of Neanderthal DNA in their genetic makeup, revealing genetic mixing was occurring.

Intimate Spin

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

Writing in the journal Evolution and Human Behavior, Brindle and her team detail how, to investigate the historical roots of intimate contact, they first had to come up with a description that was not limited to how people smooch.

Defining Kissing

"Previously there were some efforts to define a intimate act, but it's largely focused on humans, which implies that basically other animals do not engage in this. Now we know that they likely engage, it might just not look from what our intimate contact looks like," said Brindle.

However, she noted some behaviors that resembled kissing were distinct activities – such as the processing and food sharing, or "mouth contact", observed in aquatic species known as French grunts.

As a result the research group developed a description of kissing based on friendly interactions involving directed oral interaction with a individual of the identical group, with some motion of the mouth but no transfer of nutrition.

Research Approach

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

Scientists then integrated this data with details on the genetic connections between living and extinct types of such primates.

Historical Origins

The team say the results indicate kissing evolved somewhere between 21.5 million and 16.9 million years ago in the ancestors of the large apes.

The position of ancient hominins on this evolutionary lineage means it is probable they, too, engaged in a intimate act, the researchers say. But the activity might not have been confined to their specific group.

"The fact that humans kiss, the reality that we currently have demonstrated that Neanderthals probably kissed, indicates that the two [species] are also likely to have engage," the researcher noted.

Evolutionary Importance

While the evolutionary explanation is debated, the expert said kissing could be employed in sexual contexts to potentially enhance mating outcomes or help choose between mates, while it might help strengthen connections when used in a non-sexual manner.

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 origins lie deep in our ancient history, and an examination of various types of kissing among a wider variety of species might push its beginnings back further still.

"Behaviors that we think of as characteristics of human life, like intimate contact, are not exclusive to us if we examine carefully at different species," he said.

Cultural Elements

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

"Nonetheless, as humans we thrive or fail on the quality of our emotional bonds, and ways of promoting confidence and closeness 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 ancient history, but actually it ought to be expected that Neanderthals – and including them and our human ancestors collectively – engaged intimately."