Rock music is a genre of popular music that developed during and after the 1960s, particularly in the United Kingdom and the United States. It originated in 1940s and 1950s from the rock ‘n’ roll, which itself heavily influenced and blues and country music. Rock music is also related to a number of other genres such as blues and folk, and influenced from jazz, classical and other musical sources. In the words of Bruce Dickinson, “Rock music should be gross: that's the fun of it. It gets up and drops its trousers.” The genre has become extremely diverse and common musical characteristics are difficult to define. Like pop music, lyrics often stress romantic love but also address a wide variety of other themes. In the past rock music has been dominated more often than not by white, male musicians. Rock music places a higher degree of emphasis on live performance, and advocates the need of authenticity, than pop music.