The colors of primates are among the most diverse phenotypes in mammals. These colors are mostly produced by the deposition of melanin pigments in hairs. Many species show considerable variability in pigmentation, but this is always temporarily fixed. Here the first rapid change in the pigmentation phenotype of a primate is reported. In the last five years, the pelage of mantled howler monkeys Alouatta palliata inhabiting Costa Rica has started to change from fully black to yellowish,...