Yoruba Terra-cotta head
"Today, there must be in the region of fifteen million people, mostly in Nigeria but some in the Benin Republic too, who would claim to be Yoruba. The word refers to a serie of mutually unintelligible dialects spoken by people who, in the pre-colonial period, were grouped into some fifty kingdoms that formed variable alliances in time of war but were never united, except in the sense that their kings all claimed descent form the god Oduduwa, who climbed dow from the sky at Ife to make the world. The use of the word "Yoruba", derived from a Hausa word for the kingdom of Oyo, to describe these diverse entities is a development of the colonial period and can be ascribed partly to the use of Standard Yoruba as a medium of education - in a form derived from the Oyo dialect, it was used to translate the Bible - and partly from the formation of a Yoruba political party, the Action Group, after the World Word II. The precolonial bases for this sense of Yoruba identity are much harder to discern, altough one factor was probably the mythology of kingship."
Bibliography: Werner Schmalenbach (ed.), African Art, Prestel-Verlag, Munich, 1988, p. 139