Kissing may feel like a very human habit, but new research suggests it has much deeper roots. A team of scientists says the behavior likely began more than 20 million years ago, long before modern humans existed.
Researchers from Oxford University in England reviewed decades of studies on primates to understand how kissing may have evolved.
By comparing the behavior of living species such as chimpanzees, bonobos, orangutans and one gorilla species, the team used statistical modeling to estimate when kissing first appeared.
Their results, published in the journal Evolution and Human Behavior, suggest that an ancient ancestor of today's apes likely engaged in mouth-to-mouth contact between 16.9 million and 21.5 million years ago.
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