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The shifting balance theory is a theory of
evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

evolution
proposed in 1932 by
Sewall Wright Sewall Green Wright FRS(For) Honorary FRSE Fellowship of the Royal Society of Edinburgh (FRSE) is an award granted to individuals that the Royal Society of Edinburgh, Scotland's national academy of science and Literature, letters, judged to ...

Sewall Wright
, suggesting that adaptive evolution may proceed most quickly when a
population Population typically refers the number of people in a single area whether it be a city or town, region, country, or the world. Governments typically quantify the size of the resident population within their jurisdiction by a process called a ...

population
divides into
subpopulation In statistics Statistics is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics to a scientific, industrial, or social problem, it is conventional to begin with ...
s with restricted
gene flow In population genetics Population genetics is a subfield of that deals with genetic differences within and between s, and is a part of . Studies in this branch of examine such phenomena as , , and . Population genetics was a vital ingredient ...

gene flow
. The name of the theory is borrowed from Wright's metaphor of fitness landscapes (
evolutionary landscape An evolutionary landscape is a metaphorWright, Sewall (1932) The Roles of Mutation, Inbreeding, Crossbreeding, and Selection in Evolution. ''Proceedings of the Sixth International Congress of Genetics'' 1: 356–366 or a construct used to think abou ...
s), 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 Genetic drift (allelic drift or the Sewall Wright effect) is the change in the frequency of an existing gene In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical stru ...

Genetic drift
allows a locally adapted subpopulation to move across an adaptive valley to the base of a higher adaptive peak. #
Natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype right , Here the relation between genotype and phenotype is illustrated, using a Punnett square, for the character of peta ...
will move the subpopulation up the higher peak. #This new superiorly adapted subpopulation may then expand its
range Range may refer to: Geography * Range (geographic), a chain of hills or mountains; a somewhat linear, complex mountainous or hilly area (cordillera, sierra) ** Mountain range, a group of mountains bordered by lowlands * Range, a term used to i ...
and outcompete or
interbreed In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...
with other subpopulations, causing the spread of new
adaptation In , adaptation has three related meanings. Firstly, it is the dynamic evolutionary process that fits s to their environment, enhancing their . Secondly, it is a state reached by the population during that process. Thirdly, it is a or adapti ...

adaptation
s and movement of the global population toward the new fitness peak. Although shifting balance theory has been influential in
evolutionary biology Evolutionary biology is the subfield of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interacti ...
, inspiring the theories of
quantum evolution Quantum evolution is a component of George Gaylord Simpson's multi-tempoed theory of evolution proposed to explain the rapid emergence of higher Taxonomy (biology), taxonomic groups in the fossil record. According to Simpson, Rate of evolution, ev ...
and
punctuated equilibrium In evolutionary biology Evolutionary biology is the subfield of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular ...

punctuated equilibrium
, little
empirical evidence Empirical evidence for a proposition In logic and linguistics, a proposition is the meaning of a declarative sentence (linguistics), sentence. In philosophy, "Meaning (philosophy), meaning" is understood to be a non-linguistic entity which is s ...
exists to support the shifting balance process as an important factor in evolution.


References


Further reading

* * *Wright, S. 1932. The roles of mutation, inbreeding, crossbreeding and selection in evolution. Proceedings of the 6th International Congress of Genetics: 356-366. * * {{DEFAULTSORT:Shifting Balance Theory Evolutionary biology