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Genetic drift, also known as random genetic drift, allelic drift or the Wright effect, is the change in the frequency of an existing gene variant (allele) in a population due to random chance.
Sir Ronald Aylmer Fisher was a British polymath who was active as a mathematician, statistician, biologist, geneticist, and academic. For his work in statistics, he has been described as "a genius who almost single-handedly created the foundations for modern statistical science" and "the single most important figure in 20th century statistics". In genetics, his work used mathematics to combine Mendelian genetics and natural selection; this contributed to the revival of Darwinism in the early 20th-century revision of the theory of evolution known as the modern synthesis, being the one to most comprehensively combine the ideas of Gregor Mendel and Charles Darwin. For his contributions to biology, Richard Dawkins proclaimed Fisher as "the greatest of Darwin's successors". He is considered one of the founding fathers of Neo-Darwinism.
The neutral theory of molecular evolution holds that most evolutionary changes occur at the molecular level, and most of the variation within and between species are due to random genetic drift of mutant alleles that are selectively neutral. The theory applies only for evolution at the molecular level, and is compatible with phenotypic evolution being shaped by natural selection as postulated by Charles Darwin.
Population genetics is a subfield of genetics that deals with genetic differences within and among populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and population structure.
In evolutionary biology, fitness landscapes or adaptive landscapes are used to visualize the relationship between genotypes and reproductive success. It is assumed that every genotype has a well-defined replication rate. This fitness is the "height" of the landscape. Genotypes which are similar are said to be "close" to each other, while those that are very different are "far" from each other. The set of all possible genotypes, their degree of similarity, and their related fitness values is then called a fitness landscape. The idea of a fitness landscape is a metaphor to help explain flawed forms in evolution by natural selection, including exploits and glitches in animals like their reactions to supernormal stimuli.
The handicap principle is a disputed hypothesis proposed by the Israeli biologist Amotz Zahavi in 1975. It is meant to explain how sexual selection may lead to "honest" or reliable signalling between male and female animals which have an obvious motivation to bluff or deceive each other. The handicap principle suggests that secondary sexual characteristics are costly signals which must be reliable, as they cost the signaller resources that individuals with less of a particular trait could not afford. The handicap principle further proposes that animals of greater biological fitness signal this through handicapping behaviour, or morphology that effectively lowers overall fitness. The central idea is that sexually selected traits function like conspicuous consumption, signalling the ability to afford to squander a resource. Receivers then know that the signal indicates quality, because inferior-quality signallers are unable to produce such wastefully extravagant signals.
Group selection is a proposed mechanism of evolution in which natural selection acts at the level of the group, instead of at the level of the individual or gene.
The Genetical Theory of Natural Selection is a book by Ronald Fisher which combines Mendelian genetics with Charles Darwin's theory of natural selection, with Fisher being the first to argue that "Mendelism therefore validates Darwinism" and stating with regard to mutations that "The vast majority of large mutations are deleterious; small mutations are both far more frequent and more likely to be useful", thus refuting orthogenesis. First published in 1930 by The Clarendon Press, it is one of the most important books of the modern synthesis, and helped define population genetics. It is commonly cited in biology books, outlining many concepts that are still considered important such as Fisherian runaway, Fisher's principle, reproductive value, Fisher's fundamental theorem of natural selection, Fisher's geometric model, the sexy son hypothesis, mimicry and the evolution of dominance. It was dictated to his wife in the evenings as he worked at Rothamsted Research in the day.
George Robert Price was an American population geneticist. Price is often noted for his formulation of the Price equation in 1967.
This is a list of topics in evolutionary biology.
Motoo Kimura was a Japanese biologist best known for introducing the neutral theory of molecular evolution in 1968. He became one of the most influential theoretical population geneticists. He is remembered in genetics for his innovative use of diffusion equations to calculate the probability of fixation of beneficial, deleterious, or neutral alleles. Combining theoretical population genetics with molecular evolution data, he also developed the neutral theory of molecular evolution in which genetic drift is the main force changing allele frequencies. James F. Crow, himself a renowned population geneticist, considered Kimura to be one of the two greatest evolutionary geneticists, along with Gustave Malécot, after the great trio of the modern synthesis, Ronald Fisher, J. B. S. Haldane, and Sewall Wright.
In evolutionary biology, inclusive fitness is one of two metrics of evolutionary success as defined by W. D. Hamilton in 1964:
Evolvability is defined as the capacity of a system for adaptive evolution. Evolvability is the ability of a population of organisms to not merely generate genetic diversity, but to generate adaptive genetic diversity, and thereby evolve through natural selection.
In the theory of evolution and natural selection, the Price equation describes how a trait or allele changes in frequency over time. The equation uses a covariance between a trait and fitness, to give a mathematical description of evolution and natural selection. It provides a way to understand the effects that gene transmission and natural selection have on the frequency of alleles within each new generation of a population. The Price equation was derived by George R. Price, working in London to re-derive W.D. Hamilton's work on kin selection. Examples of the Price equation have been constructed for various evolutionary cases. The Price equation also has applications in economics.
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In population genetics, the Hill–Robertson effect, or Hill–Robertson interference, is a phenomenon first identified by Bill Hill and Alan Robertson in 1966. It provides an explanation as to why there may be an evolutionary advantage to genetic recombination.
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The shifting balance theory is a theory of evolution proposed in 1932 by Sewall Wright, suggesting that adaptive evolution may proceed most quickly when a population divides into subpopulations with restricted gene flow. The name of the theory is borrowed from Wright's metaphor of fitness landscapes, attempting to explain how a population may move across an adaptive valley to a higher adaptive peak. According to the theory, this movement occurs in three steps:
- Genetic drift allows a locally adapted subpopulation to move across an adaptive valley to the base of a higher adaptive peak.
- Natural selection will move the subpopulation up the higher peak.
- This new superiorly adapted subpopulation may then expand its range and outcompete or interbreed with other subpopulations, causing the spread of new adaptations and movement of the global population toward the new fitness peak.
Genetic variance is a concept outlined by the English biologist and statistician Ronald Fisher in his fundamental theorem of natural selection. In his 1930 book The Genetical Theory of Natural Selection, Fisher postulates that the rate of change of biological fitness can be calculated by the genetic variance of the fitness itself. Fisher tried to give a statistical formula about how the change of fitness in a population can be attributed to changes in the allele frequency. Fisher made no restrictive assumptions in his formula concerning fitness parameters, mate choices or the number of alleles and loci involved.
Mark A. Kirkpatrick is a theoretical population geneticist and evolutionary biologist. He currently holds the T. S. Painter Centennial Professorship in Genetics in the Department of Integrative Biology at the University of Texas at Austin. His research touches on a wide variety of topics, including the evolution of sex chromosomes, sexual selection, and speciation. Kirkpatrick is the co-author, along with Douglas J. Futuyma, of a popular undergraduate evolution textbook. He is a member of the United States National Academy of Sciences.
References
- ↑ Crow, J.F. (2002). "Here's to Fisher, additive genetic variance, and the fundamental theorem of natural selection". Perspective. Evolution. 56 (7): 1313–1316. doi:10.1554/0014-3820(2002)056[1313:phstfa]2.0.co;2. PMID 12206233. S2CID 198157405.
- ↑ Lessard, Sabin (1997). "Fisher's Fundamental Theorem of Natural Selection Revisited". Theoretical Population Biology. 52 (2): 119–136. doi:10.1006/tpbi.1997.1324. PMID 9356328.
- 1 2 Fisher, R.A. (1930). The Genetical Theory of Natural Selection. Oxford, UK: Clarendon Press.
- ↑ Edwards, A.W.F. (1994). "The fundamental theorem of natural selection". Biological Reviews. 69 (4): 443–474. doi:10.1111/j.1469-185x.1994.tb01247.x. PMID 7999947. S2CID 10052338.
- ↑ Kimura, Motoo (1965). "Attainment of quasi-linkage equilibrium when gene frequencies are changing by natural selection". Genetics. 52 (5): 875–890. doi:10.1093/genetics/52.5.875. PMC 1210959 . PMID 17248281.
- ↑ Singh, Rama S.; Krimbas, Costas B. (28 March 2000). Evolutionary Genetics: From molecules to morphology. Cambridge University Press. p. 267. ISBN 978-0-521-57123-4.
- ↑ Provine, William B. (May 2001). The Origins of Theoretical Population Genetics: With a new afterword. University of Chicago Press. pp. 140–166. ISBN 978-0-226-68464-2.
- ↑ Price, G.R. (1972). "Fisher's "fundamental theorem" made clear". Annals of Human Genetics . 36 (2): 129–140. doi:10.1111/j.1469-1809.1972.tb00764.x. PMID 4656569. S2CID 20757537.
- ↑ Bolnick, D.I.; Nosil, P. (2007). "Natural selection in populations subject to a migration load". Evolution. 61 (9): 2229–2243. doi:10.1111/j.1558-5646.2007.00179.x. PMID 17767592.
