Citizendia
Your Ad Here

Fitness (often denoted w in population genetics models) is a central concept in evolutionary theory. Population genetics is the study of the Allele frequency distribution and change under the influence of the four evolutionary forces Natural selection, Genetic eVolution is the third Album by eLDee, it was due to be released in 2008 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. The genotype is the genetic constitution of a cell an organism or an individual (i History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance 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. Natural selection is the process by which favorable Heritable traits become more common in successive Generations of a Population of

An individual's fitness is manifested through its phenotype. A phenotype is any observable characteristic of an Organism, such as its morphology, Development, biochemical or physiological properties 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. From the time of antiquity field biologists have observed that some organisms tend to exhibit strategies that favor the reproductive success of their relatives even at a cost to their own survival

The concept is particularly difficult to understand and frequently misunderstood; J.B.S. Haldane when discussing it with John Maynard Smith is reported to have described it as "a bugger". John Burdon Sanderson Haldane FRS ( 5 November 1892 &ndash 1 December 1964) known as Jack (but who used 'J Maynard Smith redirects here -- for other uses see Maynard Smith (disambiguation Professor John Maynard Smith, F

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. A ratio is an expression which compares quantities relative to each other It is calculated for a single generation and may be calculated from absolute numbers or from frequencies. Generation (from the Greek γενεά) also known as procreation, is the act of producing Offspring. When the fitness is larger than 1. 0, the genotype increases in frequency; a ratio smaller than 1. 0 indicates a decrease in frequency.

{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. Fecundity, derived from the word fecund, generally refers to the ability to Reproduce.

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 the Arithmetic mean (and is distinguished from the Geometric mean or Harmonic mean 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). In Mathematics, a coefficient is a Constant multiplicative factor of a certain object A computer is a Machine that manipulates data according to a list of instructions. By taking the logarithm of fitness each term may be added rather than multiplied. In Mathematics, the logarithm of a number to a given base is the power or Exponent to which the base must be raised in order to produce 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. In Evolutionary biology, fitness landscapes or adaptive landscapes are used to visualize the relationship between Genotypes (or Phenotypes and Sewall Green Wright ( December 21, 1889 – March 3, 1988) was an American Geneticist 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. In Population genetics, genetic load or genetic burden is a measure of the cost of lost alleles due to Selection ( selectional load) or Mutation In Population genetics, fixation occurs when every individual within a Population has the same Allele at a particular locus.

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. Fitness (often denoted w in Population genetics models is a central concept in evolutionary theory.

P(m) = \int s(x) N(m - x)\, dx

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. Gaussian adaptation (GA is an Evolutionary algorithm designed for the maximization of manufacturing yield due to statistical deviation of component values of Signal The central limit theorem (CLT states that the sum of a sufficiently large number of identically distributed independent Random variables each with finite The second law of Thermodynamics is an expression of the universal law of increasing Entropy, stating that the entropy of an Isolated system which This is in contrast to Fisher's fundamental theorem of natural selection. In Population genetics, R A Fisher 's fundamental Theorem of Natural selection was originally stated as "The rate of increase

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 United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located Sociology (from Latin: socius "companion" and the suffix -ology "the study of" from Greek λόγος lógos "knowledge" Herbert Spencer ( April 27, 1820 – December 8, 1903) was an English Philosopher; prominent classical liberal "Survival of the fittest" is a Phrase which is shorthand for a concept relating to competition for survival or predominance 1851 ( MDCCCLI) was a Common year starting on Wednesday (link will display the full calendar of the Gregorian Calendar (or a Common year Social Statics or The Conditions essential to Happiness specified and the First of them Developed is an 1851 book by the British economist Herbert Spencer Charles Robert Darwin (February 12 1809 &ndash April 19 1882 was an English naturalist, who realised and demonstrated that all Species of life Natural selection is the process by which favorable Heritable traits become more common in successive Generations of a Population of 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. John Burdon Sanderson Haldane FRS ( 5 November 1892 &ndash 1 December 1964) known as Jack (but who used 'J Mendelian inheritance (or Mendelian genetics or Mendelism) is a set of primary tenets relating to the transmission of hereditary characteristics from parent Year 1924 ( MCMXXIV) was a Leap year starting on Tuesday (link will display the full calendar of the Gregorian calendar. A Mathematical Theory of Natural and Artificial Selection is the title of a series of Scientific papers by the British Population geneticist 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. There are a few definitions of Inclusive fitness (IF but one (that according to Oli 2003 is not consistent with W William Donald Hamilton, FRS ( 1 August 1936 &mdash 7 March 2000) was a British Evolutionary biologist Year 1964 ( MCMLXIV) was a Leap year starting on Wednesday (link will display full calendar of the 1964 Gregorian calendar. The Genetical Evolution of Social Behavior is a 1964 Scientific paper by the British Evolutionary biologist W

References

Further reading

See also

External links

The gene-centered view of evolution, gene selection theory or selfish gene theory holds that Natural selection acts through differential survival of competing There are a few definitions of Inclusive fitness (IF but one (that according to Oli 2003 is not consistent with W Natural selection is the process by which favorable Heritable traits become more common in successive Generations of a Population of Reproductive success is defined as the passing of Genes onto the next Generation in a way that they too can pass those genes on
© 2009 citizendia.org; parts available under the terms of GNU Free Documentation License, from http://en.wikipedia.org
 Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic