Clay's Ark (Patternmaster, #3)

Clay's Ark (1984) is a novel by American science fiction author Octavia E. Butler. The last published of her Patternist series, the novel serves as a prequel that accounts for the arrival of the Clay Ark disease that leads to the evolution of clayarks, the mutants that threaten human survival in the series debut novel, 1976's Patternmaster, and 1978's Survivor, which Butler later disavowed.