new study A study examining the evolution of kissing suggests that ancestors of apes and early humans such as Neanderthals likely locked lips with their friends and sexual partners. This behavior may date back to 21 million years ago.
Humanity first kisses have been recorded 4,500 years ago in Mesopotamia and ancient Egypt, but Matilda Brindle, lead author of the study and an evolutionary biologist in Oxford's Department of Biology, said kissing presented an “evolutionary mystery.”
It appears to carry high risks, such as disease transmission, but no obvious reproductive or survival benefits, she said.
“Kissing is one of the things we really wanted to understand,” Brindle, who studies primate sexual behavior, told CNN. “This is common among animals, which gives us a hint that this may be an evolved trait.”
Kissing, which the team defined as non-aggressive mouth-to-mouth contact that does not involve food, cannot be found in the fossil record, so Brindle and her colleagues took a different approach.
From the existing scientific literature, the researchers compiled information about which modern primate species observe kissing; these included chimpanzees, bonobos, orangutans and one species of gorilla.
The team then conducted phylogenetic analysis, which allows scientists to derive information about the characteristics of extinct species from data on the behavior of living animals. This involves reconstructing a tree or kinship map of different primate species based on genetic information, Brindle said.
“With this information, we can kind of travel back in time,” she said.
Prehistoric kisses
The team used statistical modeling to simulate different evolutionary scenarios along the tree's branches to estimate the likelihood that different ape ancestors kissed. For example, she said chimpanzees, bonobos and humans kiss, so it's likely that the last common ancestor of all those species kissed too. To obtain reliable estimates, the model was run 10 million times.
resultspublished Wednesday in the journal Evolution and Human Behavior, suggested that kissing is an ancient trait of the great apes, evolving in the group's ancestor between 21.5 and 16.9 million years ago.
This means that extinct human relatives, such as Neanderthals, probably kissed too. This is also possible – since scientists know that our species, Homo sapiens crossed with Neanderthals. — that humans and Neanderthals kissed each other, the study notes.
However, the model does not reveal why or how kissing evolved, Brindle said, noting that there are many uses, including assessing potential partners, foreplay, bonding, easing social tension and chewing food before passing it on to offspring.
She added that data on kissing in animals other than monkeys is limited, making it difficult to reconstruct how the trait may have evolved over time. Moreover, most of the information came from animals living in captivity or shelters. More data on kissing across species is needed, she said.
“What we've done, and this is a really important first step, is to show that this is an evolved trait,” Brindle said. “It's really ancient. But why? And it's an amazing next step if people want to pick up the mantle.”
Kissing is not a universal behavior in human society, researchers note in a new study. This was recorded in only 46% of crops. according to the 2015 document.
“We did find a strong evolutionary signal in kissing, but that doesn't mean it needs to be conserved,” Brindle explained. For some populations, she added, kissing may not be appropriate: “Primates are extremely flexible species, very intelligent, and so kissing may be useful in some contexts but not in others. And if it is not useful, then it is quite risky with a high potential for disease transmission.”
There's more to kissing than just mouth-to-mouth touching, and the study doesn't really shed much light on why people kiss the way they do, says Adriano Reis i Lameira, an evolutionary psychologist and primatologist at the University of Warwick who was not involved in the work.
“The vast majority of kisses people give are not mouth-to-mouth,” he said via email.
The study sets the stage for future research in humans and other primates to explore more subtle differences in kissing, including who to kiss and how to kiss it, says Justin Garcia, an evolutionary biologist and executive director of the Kinsey Institute, a research center specializing in the study of sexuality and relationships. Garcia, who is also the author of “Intimate animal: The Science of Love, Loyalty and Connection” did not take part in the new analysis.
“Kissing is both biological and cultural, a behavior that engages the bodily senses and clearly has some evolutionary origins, but we also know that it varies across individuals and populations,” Garcia said in an email.
“This is a remarkable example of the interaction between nature and nature, including behavior that many of us humans find so deeply intimate.”
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