A more passionate third manoeuvre, known as the touching kiss, involved the recipient touching her lover's lips with her tongue. The custom seems to have spread across Indo-European culture, with the Greeks the first Europeans to take it up. Kissing soon became central to European life, but by the late Middle Ages, the Catholic church decided it was getting out of hand. It decreed that kissing in reverence of God was acceptable, but kissing done with intent to fornicate was a mortal sin, and kissing for carnal delight a venial sin. If those church fathers were right we're all doomed.
Carnality is the key to kissing's popularity.
Your lips and tongue are two of the most sensitive areas of your body, packed with a multitude of nerve endings. Kissing releases hormones and endorphins that lift your mood. What is more, substances in saliva may play a part in the chemistry of attraction. It is the mysterious sexual chemistry between two people that clues us up to the origin of kissing, Professor Bryant says. Women subconsciously prefer the smell of men whose genes for a class of immune system proteins called the MHC are very different from their own.