1. In biology, an adaptation is a peculiarity of structure, physiology, or behavior, which promotes the ability of an organism to survive and reproduce in a given environment.
2. It may also refer to the development of such characteristics by a species over time.
In the second of these senses, adaptation is the process of modification of the form or functions of part of an organism, to fit it for its environment and so to achieve efficiency in life and reproduction. Adaptation of individual organisms is called acclimatization and is temporary since it involves acquired characteristics. The permanent adaptation of species arises from transmitted genetic variations preserved by natural selection (see also evolution). Successful and versatile adaptation in an organism usually leads to widespread distribution and long-term survival. Examples include the development of lungs in amphibians, and of wings in birds and insects.
In the most general sense, adaptation is a feedback process in which external changes in an environment are mirrored by compensatory internal changes in an adaptive system. The actions of the adaptive unit can affect the environment, which, in turn, feeds information back to the adaptive system. Adaptation is evident in the evolution of both natural and artificial life systems, genetic algorithms, and social systems.
Adaptive radiation is the evolution of various divergent life-forms from a primitive and unspecialized ancestor. As the original population spreads out from its center of origin to exploit new habitats and food sources, new populations emerge, each adapted to its particular environment. Eventually, these become sufficiently distinct to be recognized as new species. Early placental mammals, for example, gave rise to modern burrowing, climbing, flying, running, and swimming forms.