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From Galápagos albatrosses to Arctic mammals, chimpanzees to great apes, various animals appear to kiss. Currently, scientists suggest that Neanderthals did it too – and might even have locked lips with early Homo sapiens.

Shared Microbial Evidence

It is not the first time scientists have proposed ancient relatives and early modern humans were closely connected. Among earlier research, researchers have discovered modern people and their Neanderthal relatives shared the same mouth microbe for millions of years after the evolutionary divergence, implying they swapped saliva.

"Probably they were kissing," the researcher noted, adding that the concept chimed with research that has found people of non-African ancestry contain ancient genetic material in their genetic makeup, revealing interbreeding was occurring.

Romantic Spin

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

Writing in the journal Evolution and Human Behavior, the researcher and her team report how, to explore the evolutionary origins of intimate contact, they first had to develop a definition that was not restricted by how people smooch.

Describing Kissing

"There have been some previous attempts to define a kiss, but it's very much been human-centric, which means that essentially non-human species don't kiss. Now we understand that they likely engage, it may appear different from what our intimate contact looks like," said the evolutionary biologist.

However, she said some actions that resembled intimate contact were distinct activities – such as the chewing and transfer of food, or "mouth contact", seen in aquatic species called certain marine animals.

Consequently the team came up with a definition of kissing based on friendly interactions involving intentional mouth-to-mouth contact with a individual of the same species, with some movement of the mouth but absence of food.

Study Methods

The lead researcher explained they focused on reports of kissing in primates from the African continent and Asia, including primates, apes and great apes, and employed digital recordings to confirm the observations.

Scientists then integrated this data with details on the evolutionary relationships between living and extinct species of such primates.

Evolutionary Origins

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 Neanderthals on this evolutionary lineage means it is likely they, too, indulged in a kiss, the scientists conclude. But the behavior might not have been limited to their specific group.

"Reality that modern people engage intimately, the reality that we currently have demonstrated that ancient relatives probably kissed, suggests that the both groups are probably did engage," the researcher noted.

Biological Significance

Although the evolutionary explanation is debated, Brindle said intimate contact could be employed in sexual contexts to possibly increase mating outcomes or assist in selecting between partners, while it might help reinforce bonding when practiced in a non-sexual manner.

Another expert in the behavior of primates said that as kissing behavior was observed in a wide range of apes it made sense its origins lie deep in our evolutionary past, and an analysis of various types of kissing among a wider variety of species might extend its origins back further still.

"Behaviors that we consider as characteristics of our species, like intimate contact, are not unique to us if we look closely at other animals," he said.

Social Aspects

An archaeology expert said that kissing had a cultural element as it was not universal to all societies.

"Nonetheless, as humans we succeed or struggle on the quality of our relationships, and methods of promoting trust and intimacy will have been important for eons," the professor stated. "This could represent an concept that appears a bit contradictory to our misplaced ideas of a supposedly aggressive and aggressive past, but actually it should be expected that Neanderthals – and including Neanderthals and our human ancestors collectively – kissed."