Jazz is a music genre that originated in the African-American communities of New Orleans, Louisiana, United States, in the late 19th and early 20th centuries, with its roots in blues and ragtime. Since the 1920s Jazz Age, it has been recognized as a major form of musical expression in traditional and popular music, linked by the common bonds of African-American and European-American musical parentage. Jazz is characterized by swing and blue notes, complex chords, call and response vocals, polyrhythms and improvisation. Jazz has roots in West African cultural and musical expression, and in African-American music traditions. As jazz spread around the world, it drew on national, regional, and local musical cultures, which gave rise to different styles. New Orleans jazz began in the early 1910s, combining earlier brass-band marches, French quadrilles, biguine, ragtime and blues with collective polyphonic improvisation. In the 1930s, heavily arranged dance-oriented swing big bands, Kansas City jazz, a hard-swinging, bluesy, improvisational style and gypsy jazz (a style that emphasized musette waltzes) were the prominent styles. Bebop emerged in the 1940s, shifting jazz from danceable popular music toward a more challenging 'musician's music' which was played at faster tempos and used more chord-based improvisation. Cool jazz developed near the end of the 1940s, introducing calmer, smoother sounds and long, linear melodic lines. The mid-1950s saw the emergence of hard bop, which introduced influences from rhythm and blues, gospel, and blues, especially in the saxophone and piano playing. Modal jazz developed in the late 1950s, using the mode, or musical scale, as the basis of musical structure and improvisation, as did free jazz, which explored playing without regular meter, beat and formal structures.