What is "selection"

Selection \Se*lec"tion\, n. [L. selectio: cf. F. s['e]lection.] . The act of selecting, or the state of being selected; choice, by preference.

2. That which is selected; a collection of things chosen; as, a choice selection of books.

Natural selection. (Biol.) See under Natural.

1620s, "act of selecting," from Latin selectionem (nominative selectio) "a choosing out, choice, selection," noun of action from past participle stem of seligere (see select (adj.)). Meaning "thing selected" is from 1805. Biological sense is from 1837; applied to actions of breeders (methodical selection), hence its use by Darwin (natural selection; 1857). French sélection is a 19c. borrowing from English.

n. 1 The process or act of select#Verb. 2 Something selected. 3 A variety of items taken from a larger collection. 4 A musical piece.

1. n. the act of choosing or selecting; "your choice of colors was unfortunate"; "you can take your pick" [syn: choice, option, pick]

2. an assortment of things from which a choice can be made; "the store carried a large selection of shoes"

3. the person or thing chosen or selected; "he was my pick for mayor" [syn: choice, pick]

4. a natural process resulting in the evolution of organisms best adapted to the environment [syn: survival, survival of the fittest, natural selection]

5. a passage selected from a larger work; "he presented excerpts from William James' philosophical writings" [syn: excerpt, extract]

Selection generally refers to the pressures on crops and organisms to evolve. These pressures include natural selection, and, in eukaryotic cells that reproduce sexually, sexual selection. Certain phenotypic traits (characteristics of an organism)—or, on a genetic level, alleles of genes—segregate within a population, where individuals with adaptive advantages or traits tend to succeeded more than their peers when they reproduce, and so contribute more offspring to the succeeding generation. When these traits have a genetic basis, selection can increase the prevalence of those traits, because offspring inherit them 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.

Whether or not selection takes place depends on the conditions in which the individuals of a species find themselves. Adults, juveniles, embryos, and gamete eggs and sperm all undergo selection. Factors fostering natural selection include sexual selection, primarily caused by mate choice in the mating phase of sexual reproduction, limits on resources (nourishment, habitat space, mates) and the existence of threats (predators, disease, adverse weather). Biologists often refer to such factors as selective or evolutionary pressures.

Natural selection has, since the 1930s, included sexual selection because biologists at the time did not think it was of great importance though it has become to be seen as more important in the 21st Century. Other subcategories of natural selection include ecological selection, stabilizing selection, disruptive selection and directional selection. Selective breeding can be seen in the breeding of dogs, and the domestication of farm animals and crops, now commonly known as selective breeding.

Selection is the stage of a genetic algorithm in which individual genomes are chosen from a population for later breeding (using the crossover operator).

A generic selection procedure may be implemented as follows:

1. The fitness function is evaluated for each individual, providing fitness values, which are then normalized. Normalization means dividing the fitness value of each individual by the sum of all fitness values, so that the sum of all resulting fitness values equals 1.
2. The population is sorted by descending fitness values.
3. Accumulated normalized fitness values are computed (the accumulated fitness value of an individual is the sum of its own fitness value plus the fitness values of all the previous individuals). The accumulated fitness of the last individual should be 1 (otherwise something went wrong in the normalization step).
4. A random number R between 0 and 1 is chosen.
5. The selected individual is the first one whose accumulated normalized value is greater than R.

For a large number of individuals the above algorithm might be computationally quite demanding. A simpler and faster alternative uses the so-called stochastic acceptance.

If this procedure is repeated until there are enough selected individuals, this selection method is called fitness proportionate selection or roulette-wheel selection. If instead of a single pointer spun multiple times, there are multiple, equally spaced pointers on a wheel that is spun once, it is called stochastic universal sampling. Repeatedly selecting the best individual of a randomly chosen subset is tournament selection. Taking the best half, third or another proportion of the individuals is truncation selection.

There are other selection algorithms that do not consider all individuals for selection, but only those with a fitness value that is higher than a given (arbitrary) constant. Other algorithms select from a restricted pool where only a certain percentage of the individuals are allowed, based on fitness value.

Retaining the best individuals in a generation unchanged in the next generation, is called elitism or elitist selection. It is a successful (slight) variant of the general process of constructing a new population.

Selection is a 1982 EP by Canadian band 54•40. It was the band's first release, appearing on the independent label Mo-Da-Mu.

Although now out of print, the album and its 1984 follow up Set the Fire were re-released in 1997 on the compilation album, Sound of Truth: The Independent Collection.

Selection may refer to:

In computing:

• Selection (user interface)
  • X Window selection
• Selection (genetic algorithm)
• Selection (relational algebra)
• Selection-based search, a search engine system in which the user invokes a search query using only the mouse
• Selection algorithm, an algorithm that finds the kth smallest number in a list

Other uses:

• Selection of candidates in British elections
• Selection (biology), selection in evolution
• A store brand used by Metro Inc.
• Selected (album), the compilation album by Recoil
• Selection (Australian history), an area of crown land acquired under legislation
• Selection (album), by 54•40
• Selection in schools, the admission of students on the basis of selective criteria
• Selection effect, a distortion of data arising from the way that the data are collected
• Selektion, selection of prisoners for execution at a Nazi concentration camp
• The Selection, a novel by Kiera Cass

Selection referred to "free selection before survey" of crown land in some Australian colonies under land legislation introduced in the 1860s. These acts were similar to the United States Homestead Act and were intended to encourage closer settlement, based on intensive agriculture, such as wheat-growing, rather than extensive agriculture, such as wool production. Selectors often came into conflict with squatters, who already occupied the land and often managed to circumvent the law.

In computing and user interface engineering, a selection is a list of items on which user operations will take place. The user typically adds items to the list manually, although the computer may create a selection automatically. Selections are enacted through combinations of key presses on a keyboard, with a precision pointing device ( mouse or touchpad and cursor, stylus), or by hand on a touchscreen device. The simultaneous selection of a group of items (either elements in a list, or discontinuous regions in a text) is called a multiple selection.

Context menus will usually include actions related to the objects included in the current selection - the selection provides the "context" for the menu.

In linguistics, selection denotes the ability of predicates to determine the semantic content of their arguments. Predicates select their arguments, which means they limit the semantic content of their arguments. One sometimes draws a distinction between types of selection; one acknowledges both s(emantic)-selection and c(ategory)-selection. Selection in general stands in contrast to subcategorization: predicates both select and subcategorize for their complement arguments, whereas they only select their subject arguments. Selection is a semantic concept, whereas subcategorization is a syntactic one.