According to James Olson - professor of History specializing on Ethnic Group studies, the Serer people "violently resisted the expansion of Islam" by the Wolof people in the 19th century, and then became a target of the 1861 jihad led by the Mandinka cleric Ma Ba Jaxoo [REF].
The Serer traditional religion is called a ƭat Roog ('the way of the Divine').