adaptation

adaptation in biology, has several meanings. It can mean the adjustment of living matter to environmental conditions and to other living things either in an organism's lifetime (physiological adaptation) or in a population over many many generations (evolutionary adaptation). The word can also refer to a trait that is considered an adaptation. The ability to adapt is a fundamental property of life and constitutes a basic difference between living and nonliving matter.

Most living things require free oxygen from the air or from water, but yeasts, many bacteria, and some other simple forms obtain the oxygen required for oxidation from molecules of substances that contain the element. Various animals and plants are adapted for securing their food and for surviving the extremes of temperature and of water supply in desert, tropical, and polar regions. For most organisms the optimum temperature is between about 20°C (68°F) and 40°C (104°F). Some algae and protozoans live in hot springs, and some bacteria can survive freezing or survive on chemicals, without light, in the ocean depths. Cacti can survive heat and drought. Certain fish and other aquatic animals live in deep water and are so specialized to withstand the great pressure that they burst if lifted to sea level.

Animals show anatomical adaptations—e.g., the body of the fish is suited to life in the water; the body of the bird is adapted for flight; and the land mammals show a wide variation in the structure of limbs and body that enables some to run swiftly, some to climb, some to swing from tree to tree, some to glide through the air, and others to jump. The whale, an aquatic mammal, can adjust to great pressure changes at different levels in the water. The beaks of birds vary in shape and size according to what they feed on—e.g., on seeds, on insects, on aquatic animals, or on small mammals. The feet and legs of birds also show modifications that fit them for perching, for wading, or for paddling through the water. Adaptive coloration is observed in many animals (see protective coloration ). Among communal insects, such as ants and honeybees, the individuals are highly adapted to perform their functions in the community.

It is believed by many scientists that life originated in the sea and that through gradual evolutionary changes some forms became adapted to life on land. Variations may arise as a result of mutation , or of recombinations of the genes in the germ cells. Such variations are inherited (see genetics ). Those that aid the organism to meet the conditions of a changing environment or help it in its competition with other living things enable it to survive and reproduce, the changes thus being passed on from one generation to another and in this way perhaps producing a new species.

See ecology ; evolution ; selection .

adaptation Adjustment by an organism to its surroundings.

Animals and plants adapt to changes in their environment through variations in structure, reproduction or organization within communities. Some such changes are temporary (acclimatization), while others may involve changes in the genetic material (DNA) and be inherited by offspring (evolution). The word is also used to describe a particular characteristic (such as body size, shape, colour, physiology, or behaviour), that enables an organism to survive in its environment.

adaptation
1. Generally, the adjustments that occur in animals in respect of their environments. The adjustments may occur by natural selection, as individuals with favourable genetic traits breed more prolifically than those lacking these traits (genotypic adaptation), or they may involve non-genetic changes in individuals, such as physiological modification (e.g. acclimatization) or behavioural changes (phenotypic adaptation). Compare abaptation.

2. (evol.) That which fits an organism both generally and specifically to exploit a given adaptive zone (e.g. wings allow birds to fly, whereas the hooked beak and sharp talons of birds of prey are more specialized adaptations well suited to a predatory way of life). The word also implies that the feature has survived because it assists its possessor in its existing niche. Compare exaptation.

3. A decrease over time of the frequency of the impulses leaving a sensory receptor when a stimulus is repeated frequently. See accommodation and habituation.