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| The '''darwin''' (d) is a [[Units of measurement|unit]] of [[evolution]]ary change, defined by [[J.B.S. Haldane]] in 1949.<ref>[[J.B.S. Haldane]] (1949). "[http://links.jstor.org/sici?sici=0014-3820(194903)3:1%3C51:SATQMO%3E2.0.CO;2-4 Suggestions as to quantitative measurement of rates of evolution]." ''[[Evolution (journal)|Evolution]]'' 3:51–56.</ref> One darwin is defined to be an [[e (mathematical constant)|e]]-fold (about 2.718) change in a [[Phenotypic trait|trait]] over one million years. Haldane named the unit after [[Charles Darwin]].
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| ==Equation==
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| The equation for calculating evolutionary change in darwins (<math>r</math>) is:
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| :<math>r=\frac{{\rm ln} X_2 - {\rm ln} X_1}{\Delta t}</math> | |
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| where <math>X_1</math> and <math>X_2</math> are the initial and final values of the trait and <math>\Delta t</math> is the change in time in millions of years. An alternative form of this equation is:
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| :<math>r=\frac{{\rm ln} \frac{X_2}{X_1}}{\Delta t}</math>
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| Since the difference between two [[natural logarithm]]s is a [[dimension]]less [[ratio]], the trait may be measured in any [[Units of measurement|unit]]. Also for this reason the darwin is a specialist form of the inverse [[mega-annum]] (<math>Ma^{-1}</math>).
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| ==Application==
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| The measure is most useful in [[palaeontology]], where [[macroevolutionary]] changes in the dimensions of [[fossil]]s can be compared. Where this is used it is an indirect measure as it relies on [[phenotypic]] rather than [[genotypic]] data. Several data are required to overcome natural variation within a population. The darwin only measures the evolution of a particular [[Trait (biology)|trait]] rather than a [[Lineage (evolution)|lineage]]; different traits may evolve at different rates within a lineage. The evolution of traits can however be used to infer as a [[Proxy (statistics)|proxy]] the evolution of lineages.
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| Genetic information cannot be obtained from fossils, but modern (post-Haldane) techniques on extant organisms now rely on genetic data (q.v. [[phylogenetics]]).
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| ==See also==
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| <div style="column-count:1;-moz-column-count:1;-webkit-column-count:1">
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| {{Portal|Evolutionary biology}}
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| * [[Evolutionary biology]]
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| </div>
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| ==References==
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| {{Reflist}}
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| [[Category:Evolutionary biology]]
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Latest revision as of 13:29, 16 July 2014
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