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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 algaealgae
[plural of Lat. alga=seaweed], a large and diverse group of primarily aquatic plantlike organisms. These organisms were previously classified as a primitive subkingdom of the plant kingdom, the thallophytes (plants that lack true roots, stems, leaves, and flowers).
..... Click the link for more information. and protozoansprotozoan
, informal term for the unicellular heterotrophs of the kingdom Protista. Protozoans comprise a large, diverse assortment of microscopic or near-microscopic organisms that live as single cells or in simple colonies and that show no differentiation into tissues.
..... Click the link for more information. live in hot springs, and some bacteriabacteria
[pl. of bacterium], microscopic unicellular prokaryotic organisms characterized by the lack of a membrane-bound nucleus and membrane-bound organelles. Once considered a part of the plant kingdom, bacteria were eventually placed in a separate kingdom, Monera.
..... Click the link for more information. 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 colorationprotective coloration,
coloration or color pattern of an animal that affords it protection from observation either by its predators or by its prey. The most widespread form of protective coloration is called cryptic resemblance, in which various effects that supplement the
..... Click the link for more information. ). 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 mutationmutation,
in biology, a sudden, random change in a gene, or unit of hereditary material, that can alter an inheritable characteristic. Most mutations are not beneficial, since any change in the delicate balance of an organism having a high level of adaptation to its environment
..... Click the link for more information. , or of recombinations of the genes in the germ cells. Such variations are inherited (see geneticsgenetics,
scientific study of the mechanism of heredity. While Gregor Mendel first presented his findings on the statistical laws governing the transmission of certain traits from generation to generation in 1856, it was not until the discovery and detailed study of the
..... Click the link for more information. ). 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.
study of the relationships of organisms to their physical environment and to one another. The study of an individual organism or a single species is termed autecology; the study of groups of organisms is called synecology.
..... Click the link for more information. ; evolutionevolution,
concept that embodies the belief that existing animals and plants developed by a process of gradual, continuous change from previously existing forms. This theory, also known as descent with modification, constitutes organic evolution.
..... Click the link for more information. ; selectionselection.
In Darwinism, the mechanism of natural selection is considered of major importance in the process of evolution. Popular formulations sometimes envisage a struggle for existence in which direct competition for mates or for various factors in the environment (e.g.
..... Click the link for more information. .
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.
adaptationthe way in which social systems of any kind (e.g. a family group, a business firm, a nation state) ‘manage’ or respond to their environment. According to Talcott PARSONS,‘adaptation’ is one of four FUNCTIONAL PREREQUISITES which all social systems must satisfy if they are to survive. He argues that in industrial societies the need for adaptation is satisfied through the development of a specialized subsystem, the economy. See also NEOEVOLUTIONISM.
the process of accommodation of the structure and functions of organisms (individuals, populations, and species) and their organs to the conditions of the environment. At the same time, any adaptation is also a result—that is, a concrete historical stage of adaptogenesis, the adaptive process occurring in specific habitats (biotopes) and their corresponding complexes of animal and plant species (biocenoses).
The existence of adaptation in living nature was known to biologists of the past. In the 18th century, deistic biologists developed a concept according to which the phenomenon of adaptation indicates that there is in living nature a certain primordial purposefulness, in the sense of an immanent property of forms of life. This meant a rejection of the materialistic, causative, and deterministic explanation of the phenomenon of adaptation. The theory of primordial purposefulness was refuted only in the second half of the 19th century by Darwin’s theory of evolution. Darwin established in 1859 that the evolution of forms of life (primarily, of species) is brought about by the evolution of their adaptations to the environment. Since that time, the view has become established in biology that adaptation is not something inherent in organisms and imparted to them beforehand but, rather, that it always arises and develops under the influence of the three basic factors of organic evolution—variability, heredity, and natural selection (as well as artificial selection—that is, selection carried out by man).
Related to the evolutionary historical aspect of adaptation are nonhereditary adaptive reactions of the organism (modifications) in response to changes in the conditions of life. The adaptiveness of its organization ensures the survival of any organism, increases its rate of reproduction, and lowers its mortality rate. Adaptation is most clearly manifested in the dynamic correspondence of the morphophysiologic organization and adaptive reactions of an animal or plant to the typical and most important conditions of the environment in which this organism has developed. The form and function of all organs, as well as of their sum total in an organism, are always correlated and coadapted—that is, they correspond to each other. For example, in many cases the protective coloration of insects matches the typical “resting posture” assumed by the insect when it settles on the surface that conceals it. Analysis of the organization of any animal or plant always reveals an amazing correspondence of the form and functions of the organism to the conditions of its environment. Thus, among marine mammals, dolphins possess the most perfect adaptations to rapid movement in an aqueous medium: they are torpedo-shaped and have a special structure of the skin and subcutaneous cellular tissue that increases the body’s streamlining and, consequently, the speed of sliding through the water. The investigation of the mechanisms of adaptation of various forms of life for the purpose of using them as models for the development of various technological devices is the main goal of bionics.
Within each group of organisms, a more thorough study of adaptations and their classification is possible. For example, adaptations in mammals can be grouped according to type of habitat (terrestrial forms, or chthonobionts; soil-inhabiting forms, or edaphobionts; arboreal forms, or dendrobionts; aquatic forms, or hydrobionts; aerial forms, or aviabionts; and so on), according to form of nutrition (granivores, herbivores, carnivores, and so on), or according to means of locomotion (leaping, running, climbing, and burrowing forms), among others. The organization of mammals is characterized by adaptations that correspond strictly to their ecologic features—that is, it is comprehensively adapted to all the principal conditions of life. Thus, the European mole (Talpa europaea ) has a cylindrical body, powerful forelegs with strongly developed claws, whose position fully corresponds to their burrowing function, and a vertical orientation of the hairs (the spines of the hairs do not curve back at the top, as in chthonobionts), which permits the mole to move easily both forward and backward through a narrow subterranean passage.
Strict adaptation to the principal environmental conditions is very typical and widespread in all groups of organisms, including plants. The structure and form of the root system, the stem, the leaves, and especially the reproductive organs are characterized by a marked adaptation. The study of the organs of sexual reproduction of phanerogams provides the most striking examples of morphological and functional adaptation. The blossoms of many plants are adapted to pollination by definite species of insects or birds.
If there is a change in the conditions of life, adaptation may lose its adaptive value. In such cases, the relative nature of adaptation becomes clearly apparent. Thus, the incisors of a hare maintained for a long time on a soft diet grow excessively. Partridges who have not yet replaced their summer plumage by winter plumage are easily visible in an early snow. Animal behavior also does not always correspond to the concrete conditions of life.
The sources of evolutionary historic adaptation are hereditary or genetic changes, mutations, which are characterized by an enormous diversity, just as the diversity of changes in the material basis of heredity—deoxyribonucleic acid (DNA)—is inexhaustible. However, the accumulation over generations of even minor mutational changes does not lead to adaptation but, on the contrary, has a disintegrating effect: it disrupts the adaptive organization that has become established in the history of any animal or plant species. I. I. Shmal’gauzen (1942, 1946) used this fact as evidence in favor of the proposition that adaptation cannot be reduced to a mutational process and regarded as an elementary consequence of rearrangements of DNA. A dialectical contradiction thus arises between mutations and adaptation (as a historical process); this contradiction can be resolved only by selection, which transforms the mutational shifts and changes into adaptation. Since the crossing of individuals of every animal and plant species (including the self-pollinators) results in genetic combinations, selection proceeds not according to mutant characteristics but according to combinational forms. A natural heterozygosis becomes established in populations, under whose conditions the adaptive morphophysiological organization bases itself not on mutations but, rather, on combinations. The heterozygosis of populations characterizes their morphophysiological unity, the community of their species characteristics. This principle of the interrelations between mutations and adaptation (including the adaptation of domestic forms of animals and plants under conditions of artificial selection) has also been accepted in agriculture: the more heterozygous a breed is, the more stable it is. Thus, mutations and their combination under the control of selection become the source of adaptation, while selection takes on the significance of the leading creative factor in the adaptive organization of the forms of life.
REFERENCESKislovskii, D. “Problema porody i ee uluchsheniia.” Trudy Moskovskogo zootekhnicheskogo instituta, vol. 2, 1935.
Shmal’gauzen, I. I. Organizm kak tseloe v individual’nom i is toricheskom razvitii. Moscow-Leningrad, 1942.
Shmal’gauzen, I.I. Faktory evoliutsii. Moscow-Leningrad, 1968.
Cott, H. Prisposobitel’naia okraska zhivotnykh. Moscow, 1950. (Translated from English.)
Darwin, C. “Proiskhozhdenie vidov. . . .” Works, vol. 3. Moscow-Leningrad, 1939.
Zelikman, A. L. “Organicheskaia tselesoobraznost’ i estestvennyi otbor.” In the collection Sovremennye problemy evoliutsionnoi teorii. Leningrad, 1967.
Paramonov, A. A. “Puti i zakonomernosti evoliutsionnogo protsessa.” Sovremennye problemy evoliutsionnoi teorii. Leningrad, 1967.
A. A. PARAMONOV