I hate to use a wiki, but I am not up to real digging for research at the moment...
An adaptation is a positive characteristic of an organism that has been favored by natural selection and increases the fitness of its possessor.[1][2] 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 sometimes used to refer to a change in an individual organism over the course of its life that makes it more suited to the environment. For an example, see Adaptation (eye). More specifically, however, such changes are referred to as acclimation or acclimatization, the former generally being a very short-term response such as shivering, the latter being a longer-term change such as sun tanning.[3]
There is a great difference between selective adaptation and acclimatization. Adaptation occurs over many generations; it is a gradual process caused by natural selection. Acclimatization generally occurs within a single lifetime and copes with issues that are less threatening. For example, if a human was to move to a higher altitude, respiration and physical exertion would become a problem, but after spending time in high altitude conditions one may acclimate or acclimatize to the pressure and function and no longer notice the change. This ability to acclimate is an adaptation, but not the acclimatization itself.
A counter-adaptation is an adaptation that has evolved due to the selective pressure of another adaptation. This occurs in an evolutionary arms race, where a new adaptation giving one species an advantage is countered by the appearance and spread of a new feature that reduces the effectiveness of the first adaptation.
Adaptation - Wikipedia, the free encyclopedia
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