Kissing, for all popularity, is a bit of a mystery. Scientists have long debated when humans’ ancestors first put their lips together, and whether the act is simply a cultural trait. A new study suggests giving someone a peck has a long history, dating up to around 21 million years ago, long before modern humans existed. The work was published in the journal Evolution and Human Behavior on November 19.

The first kiss in history probably took place over 16.9 million years ago — long before humans even existed, a new study suggests.

We do it sitting in a tree, under the mistletoe, at midnight to ring in the new year. In fairytales, the act transforms frogs into princes and awakens heroines from enchanted slumber. We make up with it, seal with it, and – in Romeo Montague’s case at least – die with it.

Is deep kissing a universal human behavior?

A new study finds that half of human cultures don’t practice romantic lip-on-lip kissing. Animals don’t tend to bother either. So how did it evolve?

Humans are born with instincts for crying and smiling, but not for kissing. Sometime in the past, our ancestors had the idea to smack their mouths together and call it romantic. And though we may not know who gave the first smooch, ancient records of these steamy sessions are helping us piece together when people started locking lips.

When was the first kiss? Recent papers have suggested that romantic or sexual kissing began 3,500 years ago in what is now India. But a new review paper in the journal Science says that this style of kissing is also mentioned in clay tablets from Mesopotamia that predate the Indian texts by about a thousand years.

There are different perspectives behind our reasoning for kissing. The history of kissing is also very diverse, from being an instinct from breastfeeding to having to do with chimpanzees’ habits.