Editing Natural selection (section)

===Heritable variation, differential reproduction===
[[File:Lichte en zwarte versie berkenspanner crop.jpg|thumb|upright=1.2|During the [[Industrial Revolution]], pollution killed many [[lichen]]s, leaving tree trunks dark. A [[industrial melanism|dark (melanic)]] morph of the [[peppered moth]] largely replaced the formerly usual light morph (both shown here). Since the moths are subject to [[predation]] by birds hunting by sight, the colour change offers better [[camouflage]] against the changed background, suggesting natural selection at work.]]
{{Main|Genetic variation}}

Natural variation occurs among the individuals of any population of organisms. Some differences may improve an individual's chances of surviving and reproducing such that its lifetime reproductive rate is increased, which means that it leaves more offspring. If the traits that give these individuals a reproductive advantage are also [[heritable]], that is, passed from parent to offspring, then there will be differential reproduction, that is, a slightly higher proportion of fast rabbits or efficient algae in the next generation. Even if the reproductive advantage is very slight, over many generations any advantageous heritable trait becomes dominant in the population. In this way the [[natural environment]] of an organism "selects for" traits that confer a reproductive advantage, causing evolutionary change, as Darwin described.<ref name=Michigan>{{cite web |title=Evolution and Natural Selection |url=http://www.globalchange.umich.edu/globalchange1/current/lectures/selection/selection.html |publisher=University of Michigan |access-date=9 November 2016 |date=10 October 2010}}</ref> This gives the appearance of purpose, but in natural selection there is no intentional choice.{{efn|In [[sexual selection]], a female animal making a choice of mate may be argued to be intending to get the best mate; there is no suggestion that she has any intention to improve the bloodline in the manner of an animal breeder.}} Artificial selection is [[Teleology|purposive]] where natural selection is not, though [[teleology in biology|biologists often use teleological language]] to describe it.<ref name=Stanford>{{cite web |title=Teleological Notions in Biology |url=http://plato.stanford.edu/entries/teleology-biology/ |website=Stanford Encyclopedia of Philosophy |access-date=28 July 2016 |date=18 May 2003}}</ref>

The [[peppered moth]] exists in both light and dark colours in Great Britain, but during the [[Industrial Revolution]], many of the trees on which the moths rested became blackened by [[soot]], giving the dark-coloured moths an advantage in hiding from predators. This gave dark-coloured moths a better chance of surviving to produce dark-coloured offspring, and in just fifty years from the first dark moth being caught, nearly all of the moths in industrial [[Manchester]] were dark. The balance was reversed by the effect of the [[Clean Air Act 1956]], and the dark moths became rare again, demonstrating the influence of natural selection on [[peppered moth evolution]].<!--<ref name="Peppered Moth">{{cite web |url=http://www.millerandlevine.com/km/evol/Moths/moths.html |title=The Peppered Moth – An Update |last=Miller |first=Kenneth R. |author-link=Kenneth R. Miller |date=August 1999 |website=millerandlevine.com |publisher=Miller And Levine Biology |access-date=9 November 2016}}</ref>--><ref>{{cite journal|last1=van't Hof |first1=Arjen E. |last2=Campagne |first2=Pascal |last3=Rigden |first3=Daniel J |display-authors=etal |title=The industrial melanism mutation in British peppered moths is a transposable element |journal=Nature |date=June 2016 |volume=534 |issue=7605 |pages=102–105 |doi=10.1038/nature17951 |pmid=27251284|bibcode=2016Natur.534..102H |s2cid=3989607 }}</ref> A recent study, using image analysis and avian vision models, shows that pale individuals more closely match lichen backgrounds than dark morphs and for the first time quantifies the [[camouflage]] of moths to [[predation]] risk.<ref name=Walton2018>{{cite journal |last1=Walton |first1=Olivia |last2=Stevens |first2=Martin |title=Avian vision models and field experiments determine the survival value of peppered moth camouflage |journal=Communications Biology |date=2018 |volume=1 |page=118 |doi=10.1038/s42003-018-0126-3 |pmid = 30271998|pmc=6123793 }}</ref>