This may come as a shock to those sitting in the back row of the cinema, but kissing is largely a cultural thing. You can blame it on the boogie or the booze, but not on your genes. Even if our primate ancestors did it, kissing is by no means universal in human cultures. People living on the island of Mangia in the South Pacific, for example, were passionate lovers but knew nothing of kissing until Europeans arrived in the 1700s. But if kissing is learned and not innate, then somebody, somewhere, must have started smooching, and then persuaded a whole load of other people to take it up too.
Theories abound as to the origins of kissing.
Some think it dates back millions of years, and started when women chewed up pieces of food and passed them directly from their lips to their babies' mouths. If our ancient human ancestors did kiss, they were coy about depicting it. One of the earliest references comes from India, about 1500 BC, when the Vedic Sanskrit texts were written down from oral history. These describe the custom of rubbing and pressing noses together. By the 6th century AD, the Indian erotic text the Kama Sutra was full of references to kissing.