An adaptation is a characteristic that improves an organism's survival and reproduction in a particular environment. In evolutionary biology, the term can describe the trait itself, the state of being suited to an environment, or the evolutionary process that produces such traits.
Adaptations arise over generations through natural selection. Individuals in a population vary, some differences are heritable, and traits that increase reproductive success tend to become more common. Examples include the insulating fur of Arctic mammals, specialized beaks in birds, and drought-tolerant features in desert plants.
An adaptation is not simply any useful change. It must have an evolutionary history shaped by selection; a temporary adjustment, such as sweating when overheated, is acclimatization or physiological regulation rather than an inherited adaptation. Mutation and recombination generate variation, while heritability allows useful differences to be passed on. Adaptation also does not mean perfection: environments change, traits involve trade-offs, and a species may remain vulnerable despite being well suited to its current habitat.