Sam Charters, related to kora music. The music of the Akonting and that played by on the banjo by elder African-American banjo players, even into the mid 20th century is easily identified as being very similar. The akonting is perhaps the most important and concrete link that exists between African and African-American music. While the findings of Kubik and others clearly attest to the essential Africanness of many essential aspects of blues expression, studies by Willie Ruff and others have situated the origin of "black" spiritual music inside enslaved peoples' exposure to their masters' Hebridean-originated gospels. African-American economist and historian Thomas Sowell also notes that the southern, black, ex-slave population was acculturated to a considerable degree by and among their Scots-Irish "redneck" neighbors. Additionally, there are theories that the four-beats-per-measure structure of the blues might share its origins with the Native American tradition of pow wow drumming. Other African influence The historian Sylviane Diouf and ethnomusicologist Gerhard Kubik identify Islamic music as an influence on blues music. Diouf notes a striking resemblance between the Islamic call to prayer (originating from Bilal ibn Rabah, a famous Abyssinian African Muslim in the early 7th century) and 19th-century field holler music, noting that both have similar lyrics praising God, melody, note changes, "words that seem to quiver and shake" in the vocal chords, dramatic changes in musical scales, and nasal intonation. She attributes the origins of field holler music to African Muslim slaves who accounted for an estimated 30% of African slaves in America. According to Kubik, "the vocal style of many blues singers using melisma, wavy intonation, and so forth is a heritage of that large region of West Africa that had been in contact with the Islamic world via the Maghreb since the seventh and eighth centuries." There was particularly a significant trans-Saharan cross-fertilization between the musical traditions of the Maghreb and the Sahel. There was a difference in the music performed by the predominantly Muslim Sahelian slaves and the predominantly non-Muslim slaves from coastal West Africa and Central Africa. The Sahelian Muslim slaves generally favoured wind and string instruments and solo singing, whereas the non-Muslim slaves generally favored drums and group chants. Plantation owners who feared revolt outlawed drums and group chants, but allowed the Sahelian slaves to continue singing and playing their wind and string instruments, which the plantation owners found less threatening. Among the instruments introduced by Muslim