A mutation in monoamine oxidase (MAO) affects the evolution of stress behavior in the blind cavefish .

The neurotransmitter serotonin controls a variety of physiological and behavioral processes. In humans, mutations affecting monoamine oxidase (MAO), the serotonin-degrading enzyme, are highly deleterious. Yet, blind cavefish of the species carry a partial loss-of-function mutation in MAO (P106L) and thrive in their subterranean environment.