Plump lips are seen as sensual and desirable, and many people seek beauty treatment to enhance the look of their mouths. But ...

In the Middle East, for example, lip-locking is widely considered to be a sign of romantic love and affection, with 10 out of 10 regional cultures showing evidence of romantic kissing.

In a study published this month in American Anthropologist, researchers propose that romantic kissing isn't something everybody does; in fact, not even half the cultures surveyed lock lips in romance.

It was previously believed the earliest evidence of romantic-sexual lip kissing in humans originated in South Asia 3,500 years ago.

Think of Casablanca, where we see the romance, not the sex, between Ilsa and Rick (aka Ingrid Bergman and Humphrey Bogart). Their final kiss is pure romance, the kind that grabs you in your gut ...

It seems hard to imagine, but romantic kissing seems to be a fairly recent phenomenon in the history of mankind, according to Tomima Edmark in “The Kissing Book” (Summit, 1996).

The findings show that this form of kissing did not originate in a single place. Mesopotamia, India, and other societies separately learned to associate pecks on the lips as romantic.

The researcher, at the University of Cambridge, suggested that the custom — a lip-kissing precursor that involved rubbing and pressing noses together — developed into hardcore smooching.