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Encyclopedia > Fitness (biology)

Fitness (often denoted w in population genetics models) is a central concept in evolutionary theory. It describes the capability of an individual of certain genotype to reproduce, and usually is equal to the proportion of the individual's genes in all the genes of the next generation. If differences in individual genotypes affect fitness, then the frequencies of the genotypes will change over generations; the genotypes with higher fitness become more common. This process is called natural selection. Population genetics is the study of the distribution of and change in allele frequencies under the influence of the four evolutionary forces: natural selection, genetic drift, mutation, and migration. ... This article is about evolution in biology. ... The genotype is the specific genetic genome of an individual, in the form of DNA. It is basically ones DNA including the influence of environmental variation, it codes for the phenotype of that individual. ... For other meanings of this term, see gene (disambiguation). ... The Galápagos Islands hold 13 species of finches that are closely related and differ most markedly in the shape of their beaks. ...


An individual's fitness is manifested through its phenotype. As phenotype is affected by both genes and environment, the fitnesses of different individuals with the same genotype are not necessarily equal, but depend on the environment in which the individuals live. However, since the fitness of the genotype is an averaged quantity, it will reflect the reproductive outcomes of all individuals with that genotype. Individuals in the mollusk species Donax variabilis show diverse coloration and patterning in their phenotypes. ...


As fitness measures the quantity of the copies of the genes of an individual in the next generation, it doesn't really matter how the genes arrive in the next generation. That is, for an individual it is equally "beneficial" to reproduce itself, or to help relatives with similar genes to reproduce, as long as similar amount of copies of individual's genes get passed on to the next generation. Selection which promotes this kind of helper behaviour is called kin selection. In evolutionary biology, kin selection refers to changes in gene frequency across generations that are driven at least in part by interactions between related individuals, and this forms much of the conceptual basis of the theory of social evolution. ...

Contents

Measures of fitness

There are two commonly used measures of fitness; absolute fitness and relative fitness.


Absolute fitness (wabs) of a genotype is defined as the ratio between the number of individuals with that genotype after selection to those before selection. It is calculated for a single generation and may be calculated from absolute numbers or from frequencies. When the fitness is larger than 1.0, the genotype increases in frequency; a ratio smaller than 1.0 indicates a decrease in frequency. A ratio is a dimensionless, or unitless, quantity denoting an amount or magnitude of one quantity relative to another. ... Generation (From the Greek γιγνμαι), also known as procreation, is the act of producing offspring. ...

{w_{mathrm{abs}}} = {{N_{mathrm{after}}} over {N_{mathrm{before}}}}

Absolute fitness for a genotype can also be calculated as the product of the proportion survival times the average fecundity. Survival may refer to: Survival skills Survival kit Survivalism Survival, a studio album by Grand Funk Railroad Survival (album), a Bob Marley reggae album Survival (Doctor Who), an episode of Doctor Who Survival (television), a British wildlife television program Survival International a charity Survival Festival, Australia This is a disambiguation... Fecundity is the potential reproductive capacity of an organism or population, measured by the number of gametes (e. ...


Relative fitness is quantified as the average number of surviving progeny of a particular genotype compared with average number of surviving progeny of competing genotypes after a single generation, i.e. one genotype is normalized at w = 1 and the fitnesses of other genotypes are measured with respect to that genotype. Relative fitness can therefore take any nonnegative value, including 0.


While researchers can usually measure relative fitness, absolute fitness is more difficult. It is often difficult to determine how many individuals of a genotype there were immediately after reproduction.


The two concepts are related, and both of them are equivalent when they are divided by the mean fitness, which is weighted by genotype frequencies. In statistics, mean has two related meanings: Look up mean in Wiktionary, the free dictionary. ... In population genetics, the genotype frequency is the frequency (or proportion i. ...

{w_{abs} over bar{w_{abs}}} = {w_{rel} over bar{w_{rel}}}

Because fitness is a coefficient, and a variable may be multiplied by it several times, biologists may work with "log fitness" (particularly so before the advent of computers). By taking the logarithm of fitness each term may be added rather than multiplied. A fitness landscape, first conceptualized by Sewall Wright, is a way of visualising fitness in terms of a three-dimensional surface on which peaks correspond to local fitness maxima; it is often said that natural selection always progresses uphill but can only do so locally. This can result in suboptimal local maxima becoming stable, because natural selection cannot return to the less-fit "valleys" of the landscape on the way to reach higher peaks. In mathematics, a coefficient is a multiplicative factor of a certain object such as a variable (for example, the coefficients of a polynomial), a basis vector, a basis function and so on. ... A BlueGene supercomputer cabinet. ... Logarithms to various bases: is to base e, is to base 10, and is to base 1. ... In evolutionary biology, fitness landscapes or adaptive landscapes are used to visualize the relationship between genotypes (or phenotypes) and replicatory success. ... Sewall Green Wright ForMemRS (December 21, 1889 – March 3, 1988) was an American geneticist known for his influential work on evolutionary theory. ...


The related concept of genetic load measures the overall fitness of a population of individuals of many genotypes whose fitnesses vary, relative to a hypothetical population in which the most fit genotype has become fixed. In population genetics, genetic load or genetic burden is a measure of the cost of lost alleles due to selection (selectional load) or mutation (mutational load). ... In population genetics, fixation occurs when every individual within a population has the same allele at a particular locus. ...


History

The British sociologist Herbert Spencer coined the phrase "survival of the fittest" (though originally, and perhaps more accurately, "survival of the best fitted") in his 1851 work Social Statics and later used it to characterise what Charles Darwin had called natural selection. The British biologist J.B.S. Haldane was the first to quantify fitness, in terms of the modern evolutionary synthesis of Darwinism and Mendelian genetics starting with his 1924 paper A Mathematical Theory of Natural and Artificial Selection. The next further advance was the introduction of the concept of inclusive fitness by the British biologist W.D. Hamilton in 1964 in his paper on The Evolution of Social Behavior. Sociology is the study of the social lives of humans, groups and societies. ... Herbert Spencer (27 April 1820 – 8 December 1903) was an English philosopher and prominent classic-liberal political theorist. ... Herbert Spencer coined the phrase survival of the fittest Survival of the fittest is a phrase which is a shorthand for a concept relating to competition for survival or predominance. ... 1851 (MDCCCLI) was a common year starting on Wednesday (see link for calendar) of the Gregorian calendar (or a common year starting on Friday of the 12-day-slower Julian calendar). ... Social Statics, or The Conditions essential to Happiness specified, and the First of them Developed is a 1851 book by the British economist Herbert Spencer. ... Charles Robert Darwin (12 February 1809 – 19 April 1882) was an eminent English naturalist who achieved lasting fame by convincing the scientific community that species develop over time from a common origin. ... The Galápagos Islands hold 13 species of finches that are closely related and differ most markedly in the shape of their beaks. ... John Burdon Sanderson Haldane (November 5, 1892 - December 1, 1964), who normally used J.B.S. as a first name, was a geneticist born in Scotland and educated at Eton and Oxford University. ... The modern evolutionary synthesis (often referred to simply as the new synthesis, the modern synthesis, the evolutionary synthesis, neo-Darwinian synthesis or neo-Darwinism), generally denotes the integration of Charles Darwins theory of the evolution of species by natural selection, Gregor Mendels theory of genetics as the basis... Mendelian inheritance (or Mendelian genetics or Mendelism) is a set of primary tenets that underlie much of genetics developed by Gregor Mendel in the latter part of the 19th century. ... 1924 (MCMXXIV) was a leap year starting on Tuesday (link will display the full calendar). ... A Mathematical Theory of Natural and Artificial Selection is the title of a series of scientific papers by the British population geneticist J.B.S. Haldane, published between 1924 and 1934. ... Inclusive fitness encompasses conventional Darwinian fitness with the addition of behaviors that contribute to an organism’s individual fitness through altruism. ... This article is about the British biologist Bill Hamilton. ... 1964 (MCMLXIV) was a leap year starting on Wednesday (the link is to a full 1964 calendar). ... The Evolution of Social Behavior is a 1964 scientific paper by the British evolutionary biologist W.D. Hamilton in which he lays out a kin selection. ...


References

  • Haldane, J.B.S. (1924) "A mathematical theory of natural and artificial selection" Part 1 Transactions of the Cambridge philosophical society: 23: 19-41 link (pdf file)
  • Hamilton, W.D. (1964) "The evolution of social behavior" Journal of Theoretical Biology 1:...

See also

The gene-centric view of evolution, gene selection theory or selfish gene theory holds that natural selection acts through differential survival of competing genes, increasing the frequency of those alleles whose phenotypic effects successfully promote their own propagation. ... Inclusive fitness encompasses conventional Darwinian fitness with the addition of behaviors that contribute to an organism’s individual fitness through altruism. ... The Galápagos Islands hold 13 species of finches that are closely related and differ most markedly in the shape of their beaks. ... Reproductive success is defined as the passing of genes onto the next generation in a way that they too can pass those genes on. ...

External links

  • Evolution A-Z: Fitness
  • Stanford Encyclopedia of Philosophy entry

  Results from FactBites:
 
Fitness (biology) - Wikipedia, the free encyclopedia (669 words)
Fitness (often denoted w in population genetics models) is a central concept in evolutionary theory.
Relative fitness is quantified as the average number of surviving progeny of a particular genotype compared with average number of surviving progeny of competing genotypes after a single generation, i.e.
Because fitness is a coefficient, and a variable may be multiplied by it several times, biologists may work with "log fitness" (particularly so before the advent of computers).
  More results at FactBites »

 
 

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