The history of pharmacology would be incomplete without mention of melanophores and their impact on the fields of drug discovery and development. The striking color changes that occur in various fish, frog, reptile, and invertebrate species stand in contrast to the gradual modulation of skin tone seen in humans. Yet the two phenomena are governed by related sets of chromatophore cells: melanophores, which change the color of skin quickly, and the melanocytes of humans and other mammals, which change skin color more slowly. While melanophores and melanocytes both synthesize the dark biopolymer pigment melanin, and package it into cytoplasmic vesicles called melanosomes, the ability to quickly reposition melanosomes intracellularly distinguishes the melanophore from its nonmotile melanocyte cousin. And 72though the amount of melanin in either chromatophore subtype can increase or decrease slowly over time—a change associated with tanning in humans—only animals that possess melanophores can rapidly change their color, an adaptation which helps camouflage and protect them from predation.