Editing Stabilizing selection (section)

== Examples ==
The most common form of stabilizing selection is based on phenotypes of a population. In phenotype based stabilizing selection, the mean value of a phenotype is selected for, resulting a decrease in the phenotypic variation found in a population.<ref>{{cite journal | vauthors = Kingsolver JG, Diamond SE | title = Phenotypic selection in natural populations: what limits directional selection? | journal = The American Naturalist | volume = 177 | issue = 3 | pages = 346–57 | date = March 2011 | pmid = 21460543 | doi = 10.1086/658341 | bibcode = 2011ANat..177..346K | s2cid = 26806172 | url = https://cdr.lib.unc.edu/downloads/4b29bf868 }}</ref>

=== Humans ===
Stabilizing selection is the most common form of nonlinear selection (non-directional) in humans.<ref>{{cite journal | vauthors = Sanjak JS, Sidorenko J, Robinson MR, Thornton KR, Visscher PM | title = Evidence of directional and stabilizing selection in contemporary humans | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 115 | issue = 1 | pages = 151–156 | date = January 2018 | pmid = 29255044 | doi = 10.1073/pnas.1707227114 | pmc = 5776788 | bibcode = 2018PNAS..115..151S | doi-access = free }}</ref> There are few examples of genes with direct evidence of stabilizing selection in humans. However, most quantitative traits (height, birthweight, schizophrenia) are thought to be under stabilizing selection, due to their polygenicity and the distribution of the phenotypes throughout human populations.<ref>{{cite journal | vauthors = Simons YB, Bullaughey K, Hudson RR, Sella G | title = A population genetic interpretation of GWAS findings for human quantitative traits | journal = PLOS Biology | volume = 16 | issue = 3 | pages = e2002985 | date = 16 March 2018 | pmid = 29547617 | pmc = 5871013 | doi = 10.1371/journal.pbio.2002985 | arxiv = 1704.06707 | doi-access = free }}</ref>

* Birth Weight − A classic example of this is human birth weight. Babies of low weight lose heat more quickly and get ill from infectious diseases more easily, whereas babies of large body weight are more difficult to deliver through the pelvis. Infants of a more medium weight survive much more often. For the larger or smaller babies, the baby mortality rate is much higher.<ref>{{cite web | date = 2004 | first = Steven M. | last = Carr | name-list-style = vanc | title = Stabilizing Selection on birthweight in humans | url = https://www.mun.ca/biology/scarr/Stabilizing_Selection_in_Humans.html }}</ref> The bell curve of the human population peaks at a birth weight that the newly born babies exhibit the minimum death rate.

=== Plants ===

* Height − Another example of a trait, that might be acted on by stabilizing selection, is plant height. A plant that is too short may not be able to compete with other plants for sunlight. However, extremely tall plants may be more susceptible to wind damage. Combined, these two selection pressures select to maintain plants of medium height. The number of plants of medium height will increase while the numbers of short and tall plants will decrease.<ref>{{cite web | title = Natural Selection | url = http://www.sparknotes.com/biology/evolution/naturalselection/section1.rhtml | work = SparkNotes }}</ref>
* Cacti Spine Number − Desert populations of spiny cacti experience predation by [[Peccary|peccaries]], which consume the fleshy part of the cactus. This can be prevented by increasing the number of spines on the cactus. However, there is also a selection pressure in the opposite direction because there is a parasitic insect that will lay its eggs in spines if they are densely populated. This means that in order to manage both of these selection pressures the cacti experiences stabilizing selection to balance the appropriate number of spines to survive these different threats.<ref>{{Cite web|url=http://www.brooklyn.cuny.edu/bc/ahp/LAD/C21/C21_Stabilizing.html|title=Stabilizing Selection | website=www.brooklyn.cuny.edu |access-date=13 May 2018}}</ref>

=== Insects ===

*[[File:Squinting bush brown (Bicyclus anynana anynana).jpg|thumb|Bicyclus anynana with wing eyespot, which experiences stabilizing selection to avoid predation.]]Butterfly's Winged Eyespots − The African butterfly ''[[Bicyclus anynana]]'' exhibits stabilizing selection with its wing [[eyespot (mimicry)|eyespots]].<ref name="pmid20147150">{{cite journal | vauthors = Brakefield PM, Beldade P, Zwaan BJ | title = The African butterfly Bicyclus anynana: a model for evolutionary genetics and evolutionary developmental biology | journal = Cold Spring Harbor Protocols | volume = 2009 | issue = 5 | pages = pdb.emo122 | date = May 2009 | pmid = 20147150 | doi = 10.1101/pdb.emo122 }}</ref> It has been suggested that the circular eyespots positioned on the wings are favoured functionally compared to other shapes and sizes.<ref>{{cite journal|last1=Brakefield|first1=Paul M | name-list-style = vanc |title=The evolution–development interface and advances with the eyespot patterns of Bicyclus butterflies|journal=Heredity|date=March 1998|volume=80|issue=3|pages=265–272|doi=10.1046/j.1365-2540.1998.00366.x|doi-access=free}}</ref>
* Gall Size − The ''[[Eurosta solidaginis]]'' fly lays its eggs on the tip of plants, which then encase the larvae in a protective [[gall]]. The size of this gall is under stabilizing selection, as determined by predation. These larvae are under threat from parasitic wasps, which lay a single egg in galls containing the flies. The single wasp offspring then consumes the fly larvae to survive. Therefore, a larger gall is favored to allow more places for larvae to hide from the wasp. However, larger galls attract a different type of predation from birds, as they can penetrate large galls with their beak. Therefore, the optimal gall is moderately sized in order to avoid predation from both birds and wasps.<ref>{{cite journal | vauthors = László Z, Sólyom K, Prázsmári H, Barta Z, Tóthmérész B | title = Predation on rose galls: parasitoids and predators determine gall size through directional selection | journal = PLOS ONE | volume = 9 | issue = 6 | pages = e99806 | date = 11 June 2014 | pmid = 24918448 | pmc = 4053394 | doi = 10.1371/journal.pone.0099806 | bibcode = 2014PLoSO...999806L | doi-access = free }}</ref>

=== Birds ===

* Clutch Size − The number of eggs laid by a female bird (clutch size) is typically under stabilizing selection. This is because the female must lay as many eggs as possible to maximize the number of offspring. However, they can only lay as many eggs as they can support with their own resources. Laying too many eggs could expend all of the energy of the mother bird causing her to die and the death of the chicks. Additionally, once the eggs hatch the mother must be able to obtain enough resources to keep all of the chicks alive. Therefore, the mother typically lays a moderate amount of eggs in order to increase offspring survival and maximize the number of offspring.<ref>{{Cite web|url=https://web.stanford.edu/group/stanfordbirds/text/essays/Variation_in_Clutch.html|title=Variation in Clutch Sizes|website=web.stanford.edu|access-date=13 May 2018}}</ref>

=== Mammals ===

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*[[File:White Siberian Husky snow 2.jpg|thumb|The Siberian husky experiences stabilizing selection in terms of their leg muscles, allowing them to be strong but light.]]The Siberian husky experiences stabilizing selection in terms of their leg muscles. These dogs have to have enough muscle in order to pull sleds and move quickly. However, they also must be light enough to stay on top of the snow. This means that the leg muscles of the husky are most fit when they are moderately sized, to balance their strength and their weight.<ref>{{Cite news|url=https://biologywise.com/stabilizing-selection-definition-examples|title=A Simple Definition and Prominent Examples of Stabilizing Selection|work=BiologyWise|access-date=16 May 2018|language=en-US}}</ref>