Stories have long been swapped on awkward first kisses and princesses smooching frogs, but a new study suggests the earliest instance of two lips pressing together happened up to 21 million years ago -- prior to the existence of humans.

The study, which was published on Wednesday in the Journal of the Human Behavior and Evolution Society , found that the very first kiss likely occurred roughly 21.5 to 16.9 million years ago, before the first appearance of Homo sapiens 300,000 years ago.

"These are deep-rooted evolutionary behaviors," Matilda Brindle, an evolutionary biologist at Oxford University and lead researcher for this study, told ABC News.

Before this revelation, no study had explored the "evolutionary history" of kissing, according to the researchers.

FILE - Orang-utan baby "

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