AskDefine | Define selective

Dictionary Definition

selective adj
1 tending to select; characterized by careful choice; "an exceptionally quick and selective reader"- John Mason Brown
2 characterized by very careful or fastidious selection; "the school was very selective in its admissions"

User Contributed Dictionary

English

Adjective

  1. Of or pertaining to the process of selection.
  2. In the context of "of a person": Choosy, fussy or discriminating when selecting.
    He's very selective and spent hours in the store choosing a new shirt.
  3. In the context of "mainly|US|not comparable": Having the authority or capability to make a selection.
    In the USA, military conscription is controlled by the Selective Service.

Translations

Related terms

References

  • Dictionary.com

Extensive Definition

In the context of evolution, certain traits or alleles of a species may be subject to selection. Under selection, individuals with advantageous or "adaptive" traits tend to be more successful than their peers reproductively--meaning they contribute more offspring to the succeeding generation than others do. When these traits have a genetic basis, selection can increase the prevalence of those traits, because offspring will inherit those traits from their parents. When selection is intense and persistent, adaptive traits become universal to the population or species, which may then be said to have evolved.

Overview

Whether or not selection takes place depends on the conditions in which the individuals of a species find themselves. Adults, juveniles, embryos, and even eggs and sperm may undergo selection. Factors fostering selection include limits on resources (nourishment, habitat space, mates) and the existence of threats (predators, disease, adverse weather). Biologists often refer to such factors as selective pressures.
Natural selection is the most familiar type of selection by name. The breeding of dogs, cows and horses, however, represents "artificial selection." Subcategories of natural selection are also sometimes distinguished. These include sexual selection, ecological selection, stabilizing selection, disruptive selection and directional selection (more on these below).
Selection occurs only when the individuals of a population are diverse in their characteristics--or more specifically when the traits of individuals differ with respect to how well they equip them to survive or exploit a particular pressure. In the absence of individual variation, or when variations are selectively neutral, selection does not occur.
Meanwhile, selection does not guarantee that advantageous traits or alleles will become prevalent within a population. Through genetic drift, such traits may become less common or disappear. In the face of selection even a so-called deleterious allele may become universal to the members of a species. This is a risk primarily in the case of "weak" selection (e.g. an infectious disease with only a low mortality rate) or small populations.
Though deleterious alleles may sometimes become established, selection may act "negatively" as well as "positively." Negative selection decreases the prevalence of traits that diminish individuals' capacity to succeed reproductively (i.e. their fitness), while positive selection increases the prevalence of adaptive traits.
In biological discussions, traits subject to negative selection are sometimes said to be "selected against," while those under positive selection are said to be "selected for," as in the sentence Desert conditions select for drought tolerance in plants and select against shallow root architectures.

Types and subtypes

Patterns of selection

Aspects of selection may be divided into effects on a phenotype and their causes. The effects are called patterns of selection, and do not necessarily result from particular causes (mechanisms); in fact each pattern can arise from a number of different mechanisms. Stabilizing selection favors individuals with intermediate characteristics while its opposite, disruptive selection, favors those with extreme characteristics; directional selection occurs when characteristics lie along a phenotypic spectrum and the individuals at one end are more successful; and balancing selection is a pattern in which multiple characteristics may be favored.

Mechanisms of selection

Distinct from patterns of selection are mechanisms of selection; for example, disruptive selection often is the result of disassortative sexual selection, and balancing selection may result from frequency-dependent selection and overdominance.

Further reading

  • Selection: The Mechanism of Evolution (2nd edition published in 2008 by Oxford University Press, 553 p., ISBN 0198569726)
selective in Arabic: اصطفاء
selective in Czech: Přírodní výběr
selective in French: Sélection (biologie)
selective in Ido: Selekto
selective in Italian: Selezione artificiale
selective in Latvian: Selekcija
selective in Hungarian: Szelekció
selective in Japanese: 選択 (進化)
selective in Polish: Selekcja (zootechnika)
selective in Serbian: Селекција

Synonyms, Antonyms and Related Words

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