Adaptation

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For other senses of this word, see adaptation (disambiguation).

A biological adaptation is an anatomical structure, physiological process or behavioral trait of an organism that has evolved over a period of time by the process of natural selection such that it increases the expected long-term reproductive success of the organism. The term adaptation is also sometimes used as a synonym for natural selection, but most biologists discourage this usage.

Adaptation can be viewed as taking place over geological time, or within the lifetime of one individual or a group.

Organisms that are adapted to their environment are able to:

• get air, water, food and nutrients
• cope with physical conditions such as temperature, light and heat
• defend themselves from their natural enemies
• reproduce
• respond to changes around them

Adaptations enable living organisms to cope with environmental stresses and pressures. One common form of physical adaptation is acclimatization. Acclimatization allows the organism to survive in a new environment. Adaptation can be structural or behavioural. Structural adaptations are special body parts of an organism that help it to survive in its natural habitat (e.g., skin color, shape, body covering). Behavioural adaptations are special ways a particular organism behaves to survive in its natural habitat. Physiological adaptations are systems present in an organism that allow it to perform certain biochemical reactions (e.g., making venom, secreting slime, being able to keep a constant body temperature).

Organisms that are not suitably adapted to their environment will either have to move out of the habitat or die out. The term die out in the context of adaptation simply means that the death rate over the entire species (population, gene pool ...) exceeds the birth rate for a long enough period for the species to disappear; due to individual phenotypic plasticity, individuals will be more or less successful.

Jean-Baptiste Lamarck

It is possible for an adaptation to be poorly selected, the advantage it confers over generations decreasing, up to and including the adaptation becoming a hindrance to the species' long-term survival. This is known as maladaptation and can apply to both humans and animals in such fields as biology, psychology (where it applies to behaviors and other learned survival mechanisms) and other fields.

There is a great difference between adaptation and acclimation. Adaptation occurs over many generations; it is generally a slow process caused by natural selection. Acclimation 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 to the pressure and function and no longer notice the change.

The theory of adaptatation was first put forth by Jean-Baptiste Lamarck. His theories are also referred to as the inheritance of acquired traits.

Lamarck's theory was for a time held as an alternative scientific explanation for evolutionary change observed by Charles Darwin in the Origin of the 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.

While both theories seem similar, it is the absence of reproduction and survival in Lamarck's theory that inevitably led to the world-wide acceptance of evolution and the teaching of adaptatation as an historical aside in contemporary genetics education.

[edit] See also

• Lamarckism
• Acclimation
• Exaptation
• Evolution
• Gene-centered view of evolution
• Intragenomic conflict
• Maladaptation
• Neutral theory of molecular evolution
• Phenotypic plasticity
• Preadaptation
• Spandrel
• Jean-Baptiste Lamarck

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