When the first enslaved Africans landed on American shores in 1619, their musical traditions landed with them. Four centuries later, the primacy of African American music is indisputable, not only in this country but in much of the world. How that music has evolved, blending with or giving rise to other traditions — from African songs and dances to field hollers and spirituals, from ragtime and blues to jazz, R&B and hip-hop — is a topic of endless discussion.