Adaptation, in biology, the process by which a living thing becomes better suited to its environment. The term is also applied to the results of the process. In many organisms there are structural, functional, and color adaptations, and in animals there are also adaptations in instinctive (unlearned) behavior.

Structural Adaptations

The extensive root systems and the small leaves common to many desert plants are good examples of structural adaptation. Such roots enable the plants to collect more of the available moisture from their dry environment. Small leaves, since they provide little surface area for evaporation, reduce loss of water. The powerful forelegs and out-turned palms of the mole are structural adaptations for burrowing.

Functional Adaptations

The ability to complete its growth cycle in a short growing season is a functional adaptation that enables a plant to survive in northerly latitudes. Another example of functional adaptation is provided by the clothes moth, which has a special enzyme that enables it to digest wool.

Color Adaptations

There are three general types of color adaptation: (1) protective coloration, (2) warning coloration, and (3) mimicry.

Protective coloration enables an animal to blend in with its background. The animal is thus less likely to be seen—and, therefore, less likely to be eaten by its enemies. Protective coloration can also help make it easier for an animal that is hunting to approach its prey.

Warning coloration occurs in certain poisonous or unpleasant-tasting animals. For example, birds will not eat the monarch butterfly because of its unpleasant taste; they are able to recognize it because of its distinctive coloring.

In mimicry, a relatively defenseless animal (called the mimic) has a superficial likeness to an animal (called the model) with qualities that cause predators to avoid it. The viceroy butterfly, for example, looks very much like the monarch butterfly, and therefore birds avoid it also.

Behavioral Adaptations

Examples of behavioral adaptation can be readily found in areas where there is a marked seasonal change in the weather. Squirrels store nuts for the winter. Many birds migrate to the south to avoid cold northern winters. Wood-chucks hibernate when cold weather arrives and food becomes scarce.

Adaptation and Survival

An environment tends to eliminate living things that are not suited to it. A plant that was not adapted to conserve moisture would soon die in the desert; an animal that stood out from its surroundings would be the most likely to fall prey to its enemies. This process of elimination is called natural selection. The phrase “survival of the fittest” refers to natural selection. Natural selection is an important factor in evolution.

An example of adaptation involving natural selection is found in the case of DDT and houseflies. When this insecticide was first used in the early 1940's, almost all the flies subjected to it were killed. Some, however, survived and continued to reproduce. Eventually only this type of resistant fly was left in the areas where DDT was used over a period of years.

Adaptation is not voluntary, but is based on inherited traits. The diversity of inherited traits is chiefly a result of mutation. Mutation is any change in the inherited characteristics of an organism which results in new traits that will be passed on to the organism's descendants. In any given environment, some traits will be advantageous and others will not. (In forests, the ability of an animal to climb trees might be an adaptation for survival, but on open grasslands speed would be more advantageous.) The organism that is best suited to its environment is most likely to survive and reproduce, and the traits that are not advantageous tend gradually to be eliminated.

Adaptive Radiation and Convergence

As a result of competition for food and living space, living things tend to spread to as many areas as they can reach and survive in. The evolution from a single group to various forms adapted to different environments and ways of life is called adaptive radiation.

An example of adaptive radiation is found among the teleosts (the ray-finned fishes). The primitive or ancestral teleosts were active, elongated fishes of the open waters. From this generalized type evolved more than 20,000 species, able to live in virtually every kind of aquatic environment. Flounders with flattened bodies dwell at the bottom of the ocean, while other teleosts, such as sea horses, have adapted to life among seaweeds and coral reefs.

Groups of organisms that are only distantly related, but which live in the same type of environment, tend to develop structures that are superficially similar, because they are adaptations to the same environment. This similarity of structure evolves through a process called adaptive convergence. For example, porpoises, seals, and fishes have all developed streamlined bodies that facilitate their movement in water.