Why is kissing such a meaningful and emotionally powerful act? This is the question that concerns Canadian historian of popular culture Marcel Danesi. It was prompted by one of his students, who asked: "Why do we experience such an unhygienic act as beautiful and romantic?" At the time he was flummoxed but his book offers some fascinating answers. He downplays biological explanations for the origin of kissing and instead sees "the romantic lip kiss" emerging in the medieval period, when it signified true love as opposed to forced or arranged relationships: the kiss "heralded an age of romantic independence". Danesi's remarkable argument is that the subversive act of kissing and its spread through stories led to the birth of popular culture itself: "The courtly love tradition was the first manifestation of popular writing." He traces the kiss through literature (such as the fateful kiss in Act V of Romeo and Juliet), images, movies (DiCaprio and Winslet's kiss at the prow of the Titanic) and into the digital age. The history of popular culture at its most illuminating.

• The picture caption was amended on 10 February 2014 because the picture shows Burt Lancaster and Deborah Kerr, not Vivien Leigh as the original said.