Blues is a vocal and instrumental form of music based on the use of the blue notes and a repetitive pattern that most often follows a twelve-bar structure. It evolved in the United States in the communities of former enslaved Africans, from spirituals, praise songs, field hollers, shouts, and chants. The use of blue notes and the prominence of call-and-response patterns in the music and lyrics are indicative of the blues' West African pedigree. The blues influenced later American and Western popular music, as it became part of the genres of ragtime, jazz, bluegrass, rhythm and blues, rock and roll, hip-hop,and pop songs.