Information about Fitness (biology)
Fitness (often denoted 
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.
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.
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.
Absolute fitness (
) 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.
Absolute fitness for a genotype can also be calculated as the product of the proportion survival times the average fecundity.
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
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.
This leads to the well known Fisher's fundamental theorem of natural selection. Fisher's theorem states that: "The rate of increase in the mean fitness of any organism at any time ascribable to natural selection acting through changes in gene frequencies is exactly equal to its genic variance in fitness at that time". This may be somewhat dubious because selection takes place on the individual level, ruling the enrichment of genes (Mayr 2001). In addition, according to Maynard Smith, a population may reach a state of selective equilibrium, in which case the increase of mean fitness is equal to zero, but not necessarily the variance in fitness.
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.
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.
As another example we may mention the definition of fitness given by Maynard Smith in the following way: ”Fitness is a property, not of an individual, but of a class of individuals – for example homozygous for allele A at a particular locus. Thus the phrase ’expected number of offspring’ means the average number, not the number produced by some one individual. If the first human infant with a gene for levitation were struck by lightning in its pram, this would not prove the new genotype to have low fitness, but only that the particular child was unlucky.” This measure is certainly useful in breeding programs, but hardly as a basis of a model of an evolution selecting individuals, because evolution would hardly know if the individual may be selected or not.
Yet another possible measure has been formulated by Hartl,1981: "The fitness of the individual - having an array x of phenotypes - is the probability, s(x), that the individual will be included among the group selected as parents of the next generation." Then, the mean fitness may be determined as a mean over the set of individuals in a large population.
where N is the p. d. f. of phenotypes in the population, and m is its centre of gravity. This measure is a suitable basis of a model of an evolution selecting individuals. It may in principle take even the stroke of the lightning into consideration. In the case N is a Gaussian it is fairly easily proved that the average information (information entropy, disorder, diversity) of a large population may be maximized by Gaussian adaptation - keeping the mean fitness constant - in accordance with recapitulation, the central limit theorem, the Hardy-Weinberg law and the second law of thermodynamics. This is in contrast to Fisher's fundamental theorem of natural selection.
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Natural selection is the process by which favorable traits that are heritable become more common in successive generations of a population of reproducing organisms, and unfavorable traits that are heritable become less
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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.
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.
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.
Measures of fitness
There are two commonly used measures of fitness; absolute fitness and relative fitness.Absolute fitness (
) 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.
Absolute fitness for a genotype can also be calculated as the product of the proportion survival times the average fecundity.
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
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.
This leads to the well known Fisher's fundamental theorem of natural selection. Fisher's theorem states that: "The rate of increase in the mean fitness of any organism at any time ascribable to natural selection acting through changes in gene frequencies is exactly equal to its genic variance in fitness at that time". This may be somewhat dubious because selection takes place on the individual level, ruling the enrichment of genes (Mayr 2001). In addition, according to Maynard Smith, a population may reach a state of selective equilibrium, in which case the increase of mean fitness is equal to zero, but not necessarily the variance in fitness.
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.
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.
As another example we may mention the definition of fitness given by Maynard Smith in the following way: ”Fitness is a property, not of an individual, but of a class of individuals – for example homozygous for allele A at a particular locus. Thus the phrase ’expected number of offspring’ means the average number, not the number produced by some one individual. If the first human infant with a gene for levitation were struck by lightning in its pram, this would not prove the new genotype to have low fitness, but only that the particular child was unlucky.” This measure is certainly useful in breeding programs, but hardly as a basis of a model of an evolution selecting individuals, because evolution would hardly know if the individual may be selected or not.
Yet another possible measure has been formulated by Hartl,1981: "The fitness of the individual - having an array x of phenotypes - is the probability, s(x), that the individual will be included among the group selected as parents of the next generation." Then, the mean fitness may be determined as a mean over the set of individuals in a large population.
where N is the p. d. f. of phenotypes in the population, and m is its centre of gravity. This measure is a suitable basis of a model of an evolution selecting individuals. It may in principle take even the stroke of the lightning into consideration. In the case N is a Gaussian it is fairly easily proved that the average information (information entropy, disorder, diversity) of a large population may be maximized by Gaussian adaptation - keeping the mean fitness constant - in accordance with recapitulation, the central limit theorem, the Hardy-Weinberg law and the second law of thermodynamics. This is in contrast to Fisher's fundamental theorem of natural selection.
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.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:...
- Hartl, D. L. A Primer of Population Genetics. Sinauer, Sunderland, Massachusetts, 1981.
- Maynard Smith, J. Evolutionary Genetics. Oxford University Press, 1998.
Further reading
- Sober, E. (2001). The Two Faces of Fitness. In R. Singh, D. Paul, C. Krimbas, and J. Beatty (Eds.), Thinking about Evolution: Historical, Philosophical, and Political Perspectives. Cambridge University Press, pp.309-321. Full text
See also
External links
Population genetics is the study of the allele frequency distribution and change under the influence of the four evolutionary forces: natural selection, genetic drift, mutation and gene flow. It also takes account of population subdivision and population structure in space.
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Genotype describes the genetic constitution of an individual, that is the specific allelic makeup of an individual, usually with reference to a specific character under consideration [1].
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For a non-technical introduction to the topic, see .
A gene is a locatable region of genomic sequence, corresponding to a unit of inheritance, which is associated with regulatory regions, transcribed regions and/or other functional sequence regions...... Click the link for more information.
Natural selection is the process by which favorable traits that are heritable become more common in successive generations of a population of reproducing organisms, and unfavorable traits that are heritable become less
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phenotype describes the total physical appearance of an organism, as opposed to its genotype. This genotype-phenotype distinction was proposed by Wilhelm Johannsen in 1911 to make clear the difference between an organism's heredity and what that heredity produces.
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kin selection.
The concept was formalized by JBS Haldane (1955)[1] and W. D. Hamilton (1963)[2], while the actual term "kin selection" may first have been coined by John Maynard Smith (1964)[3]
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The concept was formalized by JBS Haldane (1955)[1] and W. D. Hamilton (1963)[2], while the actual term "kin selection" may first have been coined by John Maynard Smith (1964)[3]
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Generation (from the Greek γενεά), also known as procreation, is the act of producing offspring. It can also refer to the act of creating something inanimate such as electrical generation or cryptographic code generation.
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Survival may refer to:
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- Survival analysis
- Survival of the fittest
- Survival kit
- Survival rate
- Survival skills
- Survivalism, a survival belief based around preparation for survival after social upheaval
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Fecundity, derived from the word , generally refers to the ability to reproduce. In biology and demography, fecundity is the potential reproductive capacity of an organism or population, measured by the number of gametes (eggs), seed set or asexual propagules.
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In statistics, mean has two related meanings:
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- the arithmetic mean (and is distinguished from the geometric mean or harmonic mean).
- the expected value of a random variable, which is also called the population mean.
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In population genetics, the genotype frequency is the frequency or proportion (i.e. 0 < f < 1) of genotypes in a population.
It may be denoted thus:
Compare allele frequency.
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It may be denoted thus:
Compare allele frequency.
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In population genetics, R. A. Fisher's fundamental theorem of natural selection was originally stated as:
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- "The rate of increase in fitness of any organism at any time is equal to its genetic variance in fitness at that time.
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Fitness (often denoted 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.
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coefficient is a constant multiplicative factor of a certain object. For example, the coefficient in 9x2 is 9.
The object can be such things as a variable, a vector, a function, etc.
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The object can be such things as a variable, a vector, a function, etc.
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computer is a machine which manipulates data according to a list of instructions.
Computers take numerous physical forms. The first devices that resemble modern computers date to the mid-20th century (around 1940 - 1941), although the computer concept and various machines
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Computers take numerous physical forms. The first devices that resemble modern computers date to the mid-20th century (around 1940 - 1941), although the computer concept and various machines
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logarithm (to base b) of a number x is the exponent y that satisfies x = by. It is written logb(x) or, if the base is implicit, as log(x).
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In evolutionary biology, fitness landscapes or adaptive landscapes are used to visualize the relationship between genotypes (or phenotypes) and reproductive success. It is assumed that every genotype has a well defined replication rate (often referred to as fitness).
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Sewall Green Wright ForMemRS (December 21, 1889 – March 3, 1988) was an American geneticist known for his influential work on evolutionary theory and also for his work on path analysis. With R. A. Fisher and J.B.S. Haldane, he was a founder of theoretical population genetics.
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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). It is a value in the range , where 0 represents no load.
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In population genetics, fixation occurs when every individual within a population has the same allele at a particular locus. The allele, such as a single point mutation or whole gene, will be initially rare (e.g.
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Fitness (often denoted 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.
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Shannon entropy or information entropy is a measure of the uncertainty associated with a random variable.
Shannon entropy quantifies the information contained in a piece of data: it is the minimum average message length, in bits (if using base-2 logarithms), that must
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Shannon entropy quantifies the information contained in a piece of data: it is the minimum average message length, in bits (if using base-2 logarithms), that must
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Shannon entropy or information entropy is a measure of the uncertainty associated with a random variable.
Shannon entropy quantifies the information contained in a piece of data: it is the minimum average message length, in bits (if using base-2 logarithms), that must
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Shannon entropy quantifies the information contained in a piece of data: it is the minimum average message length, in bits (if using base-2 logarithms), that must
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Disorder may refer to :
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- Disease, an abnormality of the body or mind that causes discomfort, dysfunction, or distress (see also: types of disorders)
- Chaos, unpredictability and in the metaphysical sense, it is the opposite of law and order
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This article has been tagged since September 2007.
This article has been tagged since September 2007.
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The word recapitulation or can mean:-
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- A summary.
- A recapitulation (music) is a section of musical sonata form where the exposition is repeated in an altered form and the development is concluded.
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A central limit theorem is any of a set of weak-convergence results in probability theory. They all express the fact that any sum of many independent and identically-distributed random variables will tend to be distributed according to a particular "attractor distribution".
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Hardy–Weinberg principle is a relationship between the frequencies of alleles and the genotype of a population. The occurrence of a genotype, perhaps one associated with a disease, stays constant unless matings are non-random or inappropriate, or mutations accumulate.
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