New Delhi: The first kiss on Earth may have taken place around 21 million years ago, a new study has claimed. It presents evidence that kissing is not just cultural but evolutionary.
The study, ‘A comparative approach to the evolution of kissing’, published Wednesday in the journal Evolution and Human Behavior, found that kissing occurs in most great apes and was likely practised by Neanderthals, an extinct group of archaic humans.
Led by the University of Oxford, the researchers set out to understand the “evolutionary puzzle” of kissing. It doesn’t help survival or boost reproduction, and is in fact a good way to pass on germs, yet it’s still entrenched in human behaviour across many societies.
“In the new study, the researchers carried out the first attempt to reconstruct the evolutionary history of kissing using a cross-species approach based on the primate family tree,” said an Oxford University release.
The study also finds that certain life-history traits correlate “reasonably, but not perfectly,” with kissing across apes. These include multi-male mating systems (multiple males mating with multiple females), non-folivorous diets (species that eat fruits, seeds, insects, or meat rather than relying mostly on leaves), and premastication (adults chewing food before giving it to infants to make it easier to eat).
While humans kiss as a social ritual and an expression of attraction and affection, the researchers — biologists Matilda Brindle and Stuart West of the University of Oxford, and Catherine F Talbot of Florida Tech — looked instead at different types of kisses in primates.
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How the study was carried out
The researchers first created a map of all known examples of modern primates that have been observed kissing.
To find out whether kissing is an evolutionary trait, they built a large evolutionary family tree based on similarities and differences in genetic and behavioural characteristics. They also used modern observational data to see which among them had kissing in their repertoire.
The researchers created 10,000 family trees with slight variations and ran the model millions of times. They concluded that the first kiss probably took place among the ancestors of today’s large apes, sometime between 16.9-21.5 million years ago.
Brindle and her fellow researchers argued that kissing had an “evolutionary signature” rather than being “purely a cultural behaviour”.
So what exactly did a ‘kiss’ mean back then? For the researchers, a Washington Post report noted, it was a kiss as long as it was “directed, nonaggressive, mouth-to-mouth contact that did not involve food transfer”. To find out who was smooching and who was not, they reviewed published research and browsed YouTube videos of primates. Those who had indeed been observed kissing included orangutans, bonobos, chimps and one gorilla species, and, of course, humans.
Kissing is an integral part of human mating, pointed out Biju Dominic, a human behaviour expert and cofounder of Final Mile, a firm that applies behavioural economics and cognitive science to human decision-making.
“Sexual interaction isn’t limited to the genitals—many other aspects, including kissing, shape intimacy and bonding. Kissing is universal. Across cultures and across partners, it consistently shows up as part of human connection,” Dominic told ThePrint.
“The Kama Sutra clearly recognises the importance of kissing and describes how it fits into human intimacy.”
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What we still don’t know
The researchers caution that their study has limitations. It can only be treated as a starting point in researching the evolution of kissing.
The study suggests that kissing may have evolved independently in different hominid groups, though they consider this unlikely. They also said that there is limited data available on kissing in other animals. More research is required to see how different forms of kissing developed.
Kissing is a diverse behaviour. For one, romantic kissing is prevalent in only about 50 per cent of human cultures, Dominic said. And yet, kissing itself may be more common than is known decisively.
“Behavioural neuroscience shows strong continuities across species—from worms to rats to birds to apes, more so in touch-based behaviours,” he added.
The researchers, too, acknowledged that reducing kissing to “present” or “not observed” may not do justice to some finer points.
“Importantly, a lack of observations does not indicate that kissing does not occur in a given species. Similarly, if kissing is recorded as ‘present’, it is not necessarily a common or universal behaviour within that species,” the study said.
(Edited by Asavari Singh)