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From Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, certain species engage in mouth-to-mouth contact. Currently, researchers propose that ancient hominins did it too – and possibly locked lips with modern humans.

Shared Oral Evidence

It is not the first time scientists have suggested Neanderthals and Homo sapiens were intimately acquainted. Among earlier research, scientists have found humans and their thick-browed cousins shared the same mouth microbe for millions of years after the two species split, implying they exchanged oral fluids.

"Probably they were engaging in intimate contact," she said, adding that the idea aligned with studies that has found humans of certain genetic backgrounds contain ancient genetic material in their genetic makeup, demonstrating interbreeding was occurring.

Romantic Interpretation

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

Publishing in the journal a scientific periodical, Brindle and her team detail how, to investigate the evolutionary origins of kissing, they first had to develop a description that was not restricted by how humans kiss.

Describing Kissing

"Previously there were some previous attempts to describe a intimate act, but it's largely human-centric, which implies that basically other animals do not engage in this. Now we understand that they likely engage, it might just not look from what human kissing resembles," explained Brindle.

However, she said some behaviors that looked like kissing were distinct activities – such as the processing and transfer of food, or "kiss-fighting", observed in fish known as French grunts.

As a result the research group came up with a description of intimate contact centered around friendly interactions involving directed oral interaction with a individual of the same species, with some movement of the oral area but absence of food.

Study Methods

Brindle explained they focused on accounts of intimate behavior in primates from the African continent and Asia, including bonobos, chimpanzees and orangutans, and employed digital recordings to verify the reports.

The researchers then integrated this information with information on the evolutionary relationships between living and ancient types of such primates.

Evolutionary Timeline

The team propose the results indicate intimate contact developed somewhere between 21.5m and 16.9 million years ago in the predecessors of the large apes.

The position of Neanderthals on this family tree suggests it is likely they, too, indulged in a kiss, the researchers say. But the behavior may not have been confined to their specific group.

"Reality that modern people kiss, the fact that we currently have shown that ancient relatives very likely engaged, suggests that the two [species] are also likely to have engage," the researcher added.

Biological Significance

Although the evolutionary explanation is debated, Brindle explained kissing could be used in reproductive situations to potentially enhance mating outcomes or assist in selecting between partners, while it could assist strengthen connections when used in a non-sexual manner.

A separate researcher in the behavior of great apes commented that as intimate contact was seen in a wide range of primates it was logical its origins extend far into our evolutionary past, and an analysis of different forms of intimate behavior among a wider variety of species might extend its beginnings back further still.

"Things that we think of as signatures of human life, like kissing, are not unique to us if we examine carefully at other animals," the expert noted.

Cultural Aspects

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

"However, as humans we thrive or fail on the strength of our relationships, and ways of promoting trust and intimacy will have been significant for millions of years," the professor stated. "It might be an image that appears a bit contradictory to our misplaced ideas of a rather ruthless and ancient history, but actually it should be no surprise that ancient hominins – and including Neanderthals and our human ancestors collectively – kissed."