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Among Galápagos albatrosses to polar bears, primates to orangutans, certain species appear to kiss. Now, researchers suggest that Neanderthals also engaged in this behavior – and might even have locked lips with early Homo sapiens.

Common Oral Evidence

This isn't the initial instance scientists have suggested Neanderthals and Homo sapiens were closely connected. Among earlier research, scientists have found humans and their Neanderthal relatives possessed the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, implying they exchanged oral fluids.

"Probably they were engaging in intimate contact," she said, explaining that the concept aligned with research that has found humans of certain genetic backgrounds have bits of ancient genetic material in their genetic makeup, demonstrating interbreeding was at play.

Intimate Spin

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

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 definition that was not restricted by how people smooch.

Describing Intimate Contact

"There have been some previous attempts to describe a intimate act, but it's largely human-centric, which means that essentially non-human species don't kiss. Currently we know that they likely engage, it may appear different from what our intimate contact resembles," explained Brindle.

However, she noted some behaviors that resembled kissing were distinct activities – such as the chewing and transfer of food, or "mouth contact", observed in fish called certain marine animals.

Consequently the research group came up with a description of kissing based on friendly interactions involving directed oral interaction with a member of the identical group, with some movement of the oral area but absence of food.

Research Approach

Brindle said they concentrated on accounts of kissing in primates from Africa and Asia, including bonobos, apes and great apes, and employed digital recordings to confirm the reports.

The researchers then integrated this information with details on the evolutionary relationships between extant and ancient species of such primates.

Historical Origins

Researchers say the results suggest intimate contact developed approximately 21.5 million and 16.9 million years ago in the ancestors of the great primates.

The position of ancient hominins on this family tree means it is probable they, too, indulged in a kiss, the researchers conclude. But the activity might not have been limited to their specific group.

"The fact that modern people kiss, the reality that we currently have shown that Neanderthals probably kissed, indicates that the both groups are probably did engage," the researcher added.

Biological Importance

Although the scientific reasoning is debated, Brindle said kissing could be used in reproductive situations to possibly enhance mating outcomes or help choose between partners, while it could assist strengthen connections when practiced in a non-sexual manner.

Another expert in the behavior of primates said that as kissing behavior was observed in a broad spectrum of apes it made sense its roots extend far into our ancient history, and an examination of different forms of intimate behavior among a wider variety of animals 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 Aspects

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

"Nonetheless, as people we thrive or fail on the strength of our relationships, and methods of encouraging trust and closeness will have been important for millions of years," she said. "This could represent an concept that seems a bit contradictory to our incorrect assumptions of a rather ruthless and aggressive past, but actually it should be expected that ancient hominins – and including Neanderthals and our human ancestors together – engaged intimately."