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From seabirds to Arctic mammals, primates to great apes, various animals appear to kiss. Now, scientists suggest that Neanderthals did it too – 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 intimately acquainted. In earlier research, researchers have discovered modern people and their thick-browed cousins possessed the same mouth microbe for hundreds of thousands of years after the two species split, suggesting they swapped saliva.

"Probably they were engaging in intimate contact," the researcher noted, adding that the idea aligned with studies that has found humans of non-African ancestry contain Neanderthal DNA in their genome, revealing genetic mixing was at play.

Romantic Spin

"This offers a more romantic spin on human-Neanderthal relations," the lead researcher commented.

Writing in the publication Evolution and Human Behavior, the researcher and colleagues detail how, to explore the historical roots of intimate contact, they first had to come up with a description that was not limited to how humans kiss.

Defining Intimate Contact

"Previously there were some previous attempts to describe a kiss, but it's very much been focused on humans, which implies that basically non-human species do not engage in this. Now we know that they probably do, it may appear different from what our intimate contact looks like," explained Brindle.

Nonetheless, she said some behaviors that resembled intimate contact were distinct activities – such as the processing and food sharing, or "mouth contact", seen in aquatic species known as certain marine animals.

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

Study Methods

The lead researcher said they focused on reports of kissing in non-human species from the African continent and Asia, including bonobos, chimpanzees and orangutans, and used online videos to confirm the reports.

The researchers then combined this information with information on the genetic connections between living and ancient types of such primates.

Evolutionary Timeline

Researchers propose the results suggest kissing developed approximately 21.5 million and 16.9m years ago in the ancestors of the large apes.

The position of Neanderthals on this evolutionary lineage means it is probable they, too, indulged in a intimate act, the researchers conclude. But the behavior might not have been confined to their specific group.

"The fact that humans kiss, the fact that we now have demonstrated that Neanderthals very likely engaged, indicates that the two [species] are also likely to have engage," Brindle noted.

Biological Importance

Although the evolutionary explanation is debated, the expert said intimate contact could be employed in sexual contexts to possibly increase reproductive success or assist in selecting between mates, while it could assist reinforce bonding when used in a platonic way.

Another expert in the behavior of primates commented that as kissing behavior was seen in a wide range of primates it made sense its roots lie deep in our ancient history, and an examination of various types of intimate behavior among a wider variety of animals might extend its beginnings back further still.

"Things that we think of as characteristics of our species, like intimate contact, are not unique to us if we look closely at other animals," the expert noted.

Social Aspects

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

"Nonetheless, as people we succeed or struggle on the strength of our relationships, and ways of promoting trust and intimacy will have been important for millions of years," she said. "This could represent an concept that appears a bit contradictory to our incorrect assumptions of a supposedly aggressive and aggressive past, but really it ought to be no surprise that Neanderthals – and including them and our own species together – engaged intimately."