Professor Dennis Galvan writes that "The oral historical record, written accounts by early Arab and European explorers, and physical anthropological evidence suggest that the various Serer peoples migrated south from the Fuuta Tooro region (Senegal River valley) beginning around the eleventh century when Islam first came across the Sahara." Over generations these people, possibly Pulaar speaking herders originally, migrated through Wolof areas and entered the Siin and Saluum river valleys. This lengthy period of Wolof-Serer contact has left us unsure of the origins of shared "terminology, institutions, political structures, and practices."