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Among Galápagos albatrosses to Arctic mammals, primates to great apes, various animals appear to kiss. Now, researchers propose that ancient hominins also engaged in this behavior – and possibly locked lips with modern humans.

Common Microbial Clues

It is not the first time scientists have suggested ancient relatives and Homo sapiens were closely connected. In earlier research, researchers have found humans and their Neanderthal relatives shared the identical oral bacteria for hundreds of thousands of years after the two species split, implying they exchanged oral fluids.

"Likely they were kissing," the researcher noted, adding that the idea chimed with studies that has found humans of certain genetic backgrounds have bits of Neanderthal DNA in their genetic makeup, revealing genetic mixing was at play.

Romantic Spin

"It certainly puts a different perspective on human-Neanderthal relations," Brindle said.

Writing in the journal a scientific periodical, Brindle and her team report how, to investigate the historical roots of intimate contact, they first had to develop a description that was not restricted by how humans smooch.

Defining Kissing

"There have been some previous attempts to define a kiss, but it's very much been focused on humans, which implies that basically non-human species do not engage in this. Currently we understand that they probably do, it may appear different from what our intimate contact resembles," explained Brindle.

Nonetheless, she said some behaviors that resembled intimate contact were something rather different – such as the chewing and food sharing, or "kiss-fighting", seen in fish known as French grunts.

As a result the team developed a description of kissing centered around social behaviors involving intentional oral interaction with a individual of the identical group, with some movement of the mouth but absence of food.

Study Methods

Brindle explained they focused on accounts of intimate behavior in primates from Africa and Asian regions, including primates, apes and orangutans, and employed digital recordings to confirm the reports.

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

Historical Origins

Researchers say the findings indicate intimate contact evolved somewhere between 21.5m and 16.9m years ago in the ancestors of the great primates.

The position of Neanderthals on this family tree suggests it is probable they, too, engaged in a intimate act, the scientists conclude. But the behavior may not have been limited to their specific group.

"Reality that modern people kiss, the fact that we currently have shown that Neanderthals probably kissed, indicates that the both groups are probably did engage," Brindle noted.

Evolutionary Importance

Although the scientific reasoning is debated, Brindle explained intimate contact could be employed in reproductive situations to potentially increase reproductive success or assist in selecting between partners, while it might help reinforce bonding when used in a platonic way.

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 lie deep in our evolutionary past, and an examination of different forms of intimate behavior among a broader range of animals might push its origins back even earlier still.

"Behaviors that we consider as characteristics of our species, like kissing, are not unique to us if we look closely 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 societies.

"Nonetheless, as humans we thrive or fail on the quality of our emotional bonds, and methods of promoting confidence and intimacy will have been important for eons," she said. "This could represent an concept that appears a bit incongruous to our misplaced ideas of a supposedly aggressive and aggressive past, but actually it ought to be expected that Neanderthals – and even them and our own species collectively – kissed."