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From Galápagos albatrosses to polar bears, primates to orangutans, certain species appear to kiss. Now, researchers propose that ancient hominins also engaged in this behavior – and possibly locked lips with early Homo sapiens.

Shared Microbial Evidence

This isn't the initial instance experts have proposed Neanderthals and Homo sapiens were closely connected. Among earlier research, researchers have found humans and their Neanderthal relatives possessed the identical oral bacteria for millions of years after the two species split, implying they swapped saliva.

"Likely they were kissing," she said, explaining that the idea aligned with studies that has found people of certain genetic backgrounds contain Neanderthal DNA in their genome, revealing interbreeding was occurring.

Romantic Spin

"This offers a different spin on ancient interactions," Brindle commented.

Writing in the publication a scientific periodical, the researcher and her team report how, to investigate the evolutionary origins of kissing, they first had to develop a definition that was not restricted by how humans kiss.

Describing Kissing

"Previously there were some efforts to describe a intimate act, but it's very much been focused on humans, which means that essentially other animals do not engage in this. Now we understand that they likely engage, it might just not look from what human kissing looks like," said the evolutionary biologist.

Nonetheless, she said some actions that looked like kissing were distinct activities – such as the processing and food sharing, or "kiss-fighting", seen in fish called certain marine animals.

As a result the team came up with a description of intimate contact centered around social behaviors involving intentional oral interaction with a member of the identical group, with some motion of the oral area but absence of nutrition.

Research Methods

Brindle said they concentrated on reports of kissing in primates from Africa and Asia, including bonobos, apes and orangutans, and used digital recordings to verify the reports.

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

Historical Timeline

Researchers propose the findings indicate intimate contact developed somewhere between 21.5m and 16.9m years ago in the predecessors of the large apes.

Placement of ancient hominins on this evolutionary lineage means it is likely they, too, indulged in a kiss, the researchers say. But the behavior might not have been limited to their specific group.

"Reality that humans engage intimately, the reality that we currently have shown that Neanderthals probably kissed, indicates that the two [species] are also likely to have kissed," Brindle noted.

Evolutionary Importance

While the scientific reasoning is debated, the expert said kissing could be used in sexual contexts to possibly increase mating outcomes or assist in selecting between mates, while it might help strengthen connections when practiced in a platonic way.

Another expert in the behavior of great apes commented that as kissing behavior was seen in a wide range of primates it made sense its origins extend far into our ancient history, and an analysis of different forms of intimate behavior among a wider variety of species might push its origins back further still.

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

Cultural Elements

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

"However, as humans we succeed or struggle on the strength of our emotional bonds, and methods of promoting trust and intimacy will have been important for millions of years," she said. "It might be an concept that appears a bit contradictory to our misplaced ideas of a supposedly aggressive and ancient history, but actually it should be no surprise that Neanderthals – and including Neanderthals and our human ancestors together – kissed."