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An adaptation is a characteristic of an organism that has been favored by natural selection and increases the fitness of its possessor.^[1][3] 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.^[4]

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 is quite a varied subject and their are many main and basic types of adaptation. These include :colour (eg. mating, camoflague),behavioural (eg. finding shade for cooling purposes),functional (eg. shivering),structural (eg. wings)

Theories

Jean-Baptiste Lamarck

Lamarck's theory was for a time held as an alternative scientific explanation for evolutionary change observed by Darwin in the The Origin of Species. The classic giraffe analogy offers the best delineation between the two.

• According to Darwin, more long-necked giraffes reproduce than short-necked giraffes and as such giraffes today have long necks.

• According to Lamarck, it was giraffes stretching their necks in response to higher leaves that resulted in giraffes having long necks. (This trait being passed on to the next generation)

Although neither theory in its conception could provide a complete description of the mechanism of transmission of trait variation (i.e., particulate inheritance), many recognized Darwin's theory immediately upon publication as a more complete and empirically supported theory. Modern genetics have since established the fundamental implausibility of Lamarckian inheritance, due to the one-way nature of transcription. However, see epigenetics and Baldwinian evolution for analogous processes in modern evolutionary.

See also

• Adaptive radiation
• Coadaptation
• Exaptation
• Dual inheritance theory
• Gene-centered view of evolution
• Habituation
• Intragenomic conflict
• Lamarckism
• Neutral theory of molecular evolution
• Preadaptation
• Spandrel

References

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