The director of the Center for Cognitive Studies at Tufts University, Medford, Mass., will speak Sunday at the Castine Unitarian Church on “religion as a natural phenomenon.” Daniel C. Dennett is the author of 10 books, and his sermon will be an introduction to a forthcoming book criticizing the rise of supernaturalism. The service will be at 10:30 a.m. at the church on Court Street.