adaptation (redirected from Adaptive Evolution)

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.

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adaptation

In biology, the process by which an animal or plant becomes fitted to its environment. It is the result of natural selection acting on inherited variation. Even simple organisms must be adapted in many ways, including structure, physiology, and genetics; movement or dispersal; means of defense and attack; and reproduction and development. To be useful, adaptations must often occur simultaneously in different parts of the body.

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adaptation

1. Biology an inherited or acquired modification in organisms that makes them better suited to survive and reproduce in a particular environment

2. Physiol the decreased response of a sense organ to a repeated or sustained stimulus

3. Psychol (in learning theory) the weakening of a response to a stimulus with repeated presentation of the stimulus without reinforcement; applied mainly to innate responses

4. Social welfare alteration to a dwelling to make it suitable for a disabled person, as by replacing steps with ramps

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adaptation [‚a‚dap′tā·shən]

(genetics)

Adjustment to new or altered environmental conditions by changes in genotype (natural selection) or phenotype.

(physiology)

The occurrence of physiological changes in an individual exposed to changed conditions; for example, tanning of the skin in sunshine, or increased red blood cell counts at high altitudes.

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Adaptation (biology)

A characteristic of an organism that makes it fit for its environment or for its particular way of life. For example, the Arctic fox (Alopex lagopus) is well adapted for living in a very cold climate. Appropriately, it has much thicker fur than similar-sized mammals from warmer places; measurement of heat flow through fur samples demonstrates that the Arctic fox and other arctic mammals have much better heat insulation than tropical species. Consequently, Arctic foxes do not have to raise their metabolic rates as much as tropical mammals do at low temperatures. The insulation is so effective that Arctic foxes can maintain their normal deep body temperatures of 100^°F (38^°C) even when the temperature of the environment falls to -112^°F (-80^°C). Thus, thick fur is obviously an adaptation to life in a cold environment. See Thermoregulation

In contrast to that clear example, it is often hard to be sure of the effectiveness of what seems to be an adaptation. For example, the scombrid fishes (tunnies and mackerel) seem to be adapted to fast, economical swimming. The body has an almost ideal streamlined shape. However, some other less streamlined-looking fishes are equally fast for their sizes. There are no measurements of the energy cost of scombrid swimming, but measurements on other species show no clear relationship between energy cost and streamlining.

Evolution by natural selection tends to increase fitness, making organisms better adapted to their environment and way of life. It might be inferred that this would ultimately lead to perfect adaptation, but this is not so. It must be remembered that evolution proceeds by small steps. For example, squids do not swim as well as fish. The squid would be better adapted for swimming if it evolved a fishlike tail instead of its jet propulsion mechanism, but evolution cannot make that change because it would involve moving down from the lesser adaptive summit before climbing the higher one.