This cultural interaction most probably occurred in Senegal, where the closely linguistically related Toucouleur, Serer and Wolof people predominate, ultimately leading to the ethnogenesis of the Fulani culture, language and people before subsequent expansion throughout much of West Africa. Another version is that they were originally a Berber speaking people who crossed Senegal to pasture their cattle on the Ferlo Desert south of the Senegal River. Finding themselves cut off from their kinsmen by the other communities now occupying the fertile Senegal valley, they gradually adopted the language of their new neighbours. As their herds increased, small groups found themselves forced to move eastward and further southwards and so initiated a series of migrations throughout West Africa, which endures to the present day.