Editing Sex (section)

=== Sexual dimorphism ===
{{Main|Sexual dimorphism}}
[[File:Male and female pheasant.jpg|thumb|[[Common pheasant]]s are [[sexual dimorphism|sexually dimorphic]] in both size and appearance.]]
[[File:Beo-2.jpg|thumb|The [[common hill myna]] is sexually [[Monomorphism (biology)|monomorphic]], meaning that the external appearance of males and females is very similar.<ref>{{cite journal | vauthors = Robin VV, Sinha A, Ramakrishnan U |date=2011 |title=Determining the sex of a monomorphic threatened, endemic passerine in the sky islands of southern India using molecular and morphometric methods |url=https://www.jstor.org/stable/24078632 |journal=Current Science |volume=101 |issue=5 |pages=676–679 |jstor=24078632 |issn=0011-3891 |quote=Many species of birds are, however, monomorphic and difficult to sex visually, particularly in the field and some even in hand. Some examples are the Hill Mynah, ''Gracula religiosa'' and the Black-capped Chickadee, ''Parus atricapillus''.}}</ref>]]
In many animals and some plants, individuals of male and female sex differ in size and appearance, a phenomenon called [[sexual dimorphism]].<ref name="Choe-2019">{{cite book|title=Encyclopedia of Animal Behavior|vauthors=Choe J|date=2019|publisher=Academic Press|isbn=978-0-12-813252-4|veditors=Cox R|volume=2|pages=7–11|language=en|chapter=Body Size and Sexual Dimorphism|chapter-url={{GBurl|id=O5lnDwAAQBAJ|pg=RA1-PA7}}}}</ref> Sexual dimorphism in animals is often associated with [[sexual selection]]: the mating competition between individuals of one sex vis-à-vis the opposite sex.<ref name="Mori-2017">{{cite encyclopedia | vauthors = Mori E, Mazza G, Lovari S |title=Sexual Dimorphism | veditors = Vonk J, Shackelford T |encyclopedia=Encyclopedia of Animal Cognition and Behavior |publisher=Springer International Publishing |place=Cham |url=https://link.springer.com/referenceworkentry/10.1007%2F978-3-319-47829-6_433-1 |access-date=5 June 2021 |date=2017 |pages=1–7 |language=en |doi=10.1007/978-3-319-47829-6_433-1 |isbn=978-3-319-47829-6 }}</ref> Other examples demonstrate that it is the preference of females that drives sexual dimorphism, such as in the case of the [[stalk-eyed fly]].<ref>{{cite journal| vauthors = Wilkinson GS, Reillo PR |date=22 January 1994|title=Female choice response to artificial selection on an exaggerated male trait in a stalk-eyed fly|url=http://www.indiana.edu/~curtweb/L567/readings/Wilkinson_%26_Reillo_1994.pdf|journal=Proceedings of the Royal Society B|volume=225|issue=1342|pages=1–6|bibcode=1994RSPSB.255....1W|citeseerx=10.1.1.574.2822|doi=10.1098/rspb.1994.0001|s2cid=5769457|archive-url=https://web.archive.org/web/20060910164858/http://www.indiana.edu/~curtweb/L567/readings/Wilkinson_%26_Reillo_1994.pdf|archive-date=10 September 2006}}</ref>

[[Sex differences in humans]] include a generally larger size and more body hair in men, while women have larger breasts, wider hips, and a higher body fat percentage. In other species, there may be differences in coloration or other features, and may be so pronounced that the different sexes may be mistaken for two entirely different taxa.<ref name="Mori-2017" />

Females are the larger sex in a majority of animals.<ref name="Choe-2019" /> For instance, female [[southern black widow]] spiders are typically twice as long as the males.<ref>{{cite book | vauthors = Drees BM, Jackman J | date = 1999 | publisher = Gulf Publishing Company | location = Houston, Texas | chapter = Southern black widow spider | title = Field Guide to Texas Insects | chapter-url=http://insects.tamu.edu/fieldguide/cimg368.html|archive-url=https://web.archive.org/web/20030831114452/http://insects.tamu.edu/fieldguide/cimg368.html|archive-date=31 August 2003|access-date=8 August 2012| via = Extension Entomology, Insects.tamu.edu, Texas A&M University }}</ref> This size disparity may be associated with the cost of producing egg cells, which requires more nutrition than producing sperm: larger females are able to produce more eggs.<ref>{{cite journal |title=Is fecundity the ultimate cause of female-biased size dimorphism in a dragon lizard? |vauthors=Stuart-Smith J, Swain R, Stuart-Smith R, Wapstra E |journal=Journal of Zoology |volume=273 |issue=3 |year=2007 |pages=266–272 |doi=10.1111/j.1469-7998.2007.00324.x }}</ref><ref name="Choe-2019" /> In many other cases, the male of a species is larger than the female. Mammal species with extreme sexual size dimorphism, such as [[elephant seal]]s, tend to have highly [[Polygyny in animals|polygynous]] mating systems, presumably due to selection for success in [[intraspecific competition|competition]] with other males. 

Sexual dimorphism can be extreme, with males, such as some [[anglerfish]], living [[parasite|parasitically]] on the female. Some plant species also exhibit dimorphism in which the females are significantly larger than the males, such as in the moss genus ''[[Dicranum]]''<ref>{{cite book | vauthors = Shaw AJ |year=2000 |chapter=Population ecology, population genetics, and microevolution |pages=379–380 | veditors = Shaw AJ, Goffinet B |title=Bryophyte Biology |location=Cambridge |publisher=Cambridge University Press |isbn=978-0-521-66097-6}}</ref> and the liverwort genus ''[[Sphaerocarpos]]''.<ref name="Schuster-1984">{{cite book | vauthors = Schuster RM |year=1984 |chapter=Comparative Anatomy and Morphology of the Hepaticae |title=New Manual of Bryology |location=Nichinan, Miyazaki, Japan |publisher=The Hattori botanical Laboratory |volume=2 |page=891}}</ref> There is some evidence that, in these genera, the dimorphism may be tied to a sex chromosome,<ref name="Schuster-1984" /><ref name="Crum-1980">{{cite book | vauthors = Crum HA, Anderson LE |year=1980 |title=Mosses of Eastern North America |volume=1 |page=196 |location=New York |publisher=Columbia University Press |isbn=978-0-231-04516-2}}</ref> or to chemical signaling from females.<ref>{{cite journal | vauthors = Briggs DA |year=1965 |title=Experimental taxonomy of some British species of genus ''Dicranum'' |journal=New Phytologist |volume=64 |pages=366–386 |doi=10.1111/j.1469-8137.1965.tb07546.x |issue=3|doi-access=free |bibcode=1965NewPh..64..366B }}</ref>

In birds, males often have a more [[Animal coloration|colorful]] appearance and may have features (like the long tail of male peacocks) that would seem to put them at a disadvantage (e.g. bright colors would seem to make a bird more visible to predators). One proposed explanation for this is the [[handicap principle]].<ref>{{cite book |author-link=Amotz Zahavi | vauthors = Zahavi A, Zahavi A |year=1997 |title=The handicap principle: a missing piece of Darwin's puzzle |publisher=Oxford University Press |isbn=978-0-19-510035-8 |url=https://archive.org/details/handicapprincipl0000zeha }}</ref> This hypothesis argues that, by demonstrating he can survive with such handicaps, the male is advertising his [[Fitness (biology)|genetic fitness]] to females—traits that will benefit daughters as well, who will not be encumbered with such handicaps.