A new study that examines how kissing evolved suggests that ape ancestors and early humans like Neanderthals probably locked lips with their friends and sexual partners. The behavior may date back 21 million years.Humanity’s earliest kisses were recorded 4,500 years ago in Mesopotamia and Ancient Egypt, but Matilda Brindle, lead author of the research and an evolutionary biologist at Oxford’s Department of Biology, said kissing presents an “evolutionary conundrum.”It appears to carry high risks, such as disease transmission, while offering no obvious reproductive or survival advantage, she said.AdvertisementAdvertisementAdvertisementAdvertisement“Kissing is one of these things that we were just really interested in understanding,” Brindle, who studies sexual behavior in primates, told CNN. “It’s pervasive across animals, which gives you a hint that it might be an evolved trait.”Kissing, which the team defined as non-aggressive, mouth-to-mouth contact that doesn’t involve food, isn’t something that can be detected in the fossil record, so Brindle and her colleagues used a different approach.From existing scientific literature, the researchers collected information on which modern primate species have been observed kissing; these included chimpanzees, bonobos, orangutans and one species of gorilla.The team then ran a phylogenetic analysis, which allows scientists to infer information about traits in extinct species based on behavioral data from living animals. It involves reconstructing a tree or map of how different primate species are related based on genetic information, Brindle explained.AdvertisementAdvertisementAdvertisementAdvertisement“With that information, we can kind of travel back through time,” she said.Prehistoric kissesThe team deployed statistical modeling to simulate different evolutionary scenarios along the branches of the tree to estimate the probability that different ape ancestors kissed. For example, she said chimpanzees, bonobos and humans all kiss, so it’s likely that the last shared ancestor of all those species did, too. To give robust estimates, the model was run 10 million times.The results, published Wednesday in the journal Evolution and Human Behavior, suggested that kissing is an ancient trait in the large apes, evolving in an ancestor of that group between 21.5 million and 16.9 million years ago.This means that extinct human relatives, such as Neanderthals, were likely to have engaged in kissing, too. It’s also possible — since scientists know that our species, Homo sapiens, interbred with Neanderthals — that humans and Nea …
