An adaptation is a positive characteristic of an organism that has been favored by natural selection and increases the fitness of its possessor. Of course, an adaptation must have been adaptive at some point in an organism's evolutionary history, but such an organism's environment and ecological niche can change over time, leading to adaptations becoming redundant or even a hindrance (maladaptations). Such adaptations are termed vestigial. Adaptation vs. acclimation "Adaptation" is also someti… (More on Adaptation)