Editing Sex (section)

==Sex differences==
{{See also|Sex differences in medicine|Sex differences in intelligence|Neuroscience of sex differences|Sex differences in human physiology}}

[[Anisogamy]] is the fundamental difference between male and female.<ref name="Whitfield-2004">{{cite journal|vauthors=Whitfield J|date=June 2004|title=Everything you always wanted to know about sexes|journal=PLOS Biology|volume=2|issue=6|pages=e183|doi=10.1371/journal.pbio.0020183|pmc=423151|pmid=15208728|quote=One thing biologists do agree on is that males and females count as different sexes. And they also agree that the main difference between the two is gamete size: males make lots of small gametes—sperm in animals, pollen in plants—and females produce a few big eggs. |doi-access=free }}</ref><ref>{{cite book| vauthors = Pierce BA |url={{GBurl|id=z4pXRaZAkdkC|q=Gamete+size}}|title=Genetics: A Conceptual Approach|date=2012|publisher=W.H. Freeman|isbn=978-1-4292-3252-4|pages=74|language=en}}</ref> [[Richard Dawkins]] has stated that it is possible to interpret all the differences between the sexes as stemming from this.<ref>{{cite book| vauthors = Dawkins R |url={{GBurl|id=ekonDAAAQBAJ|q=the+selfish+gene+battle+of+the+sexes+2016}}|title=The Selfish Gene|date=2016|publisher=Oxford University Press|isbn=978-0-19-878860-7|pages=183–184|language=en|quote=However, there is one fundamental feature of the sexes which can be used to label males as males, and females as females, throughout animals and plants. This is that the sex cells or 'gametes' of males are much smaller and more numerous than the gametes of females. This is true whether we are dealing with animals or plants. One group of individuals has large sex cells, and it is convenient to use the word female for them. The other group, which it is convenient to call male, has small sex cells. The difference is especially pronounced in reptiles and in birds, where a single egg cell is big enough and nutritious enough to feed a developing baby for. Even in humans, where the egg is microscopic, it is still many times larger than the sperm. As we shall see, it is possible to interpret all the other differences between the sexes as stemming from this one basic difference.|author-link=Richard Dawkins}}</ref>

=== Sexual characteristics ===

{{excerpt|Sexual characteristics|templates=-more citations needed}}

=== 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.

=== Sex differences in behavior ===
{{See also|Sex differences in psychology|Animal sexual behaviour|Non-reproductive sexual behavior in animals|Sex differences in cognition}}

The sexes across gonochoric species usually differ in behavior. In most animal species, females invest more in parental care,<ref>{{cite book| vauthors = Kliman R |url={{GBurl|id=_r4OCAAAQBAJ|pg=RA1}} | veditors = Herridge EJ, Murray RL, Gwynne DT, Bussiere L |title=Encyclopedia of Evolutionary Biology|year=2016|publisher=Academic Press|isbn=978-0-12-800426-5|volume=2|pages=453–454|language=en }}</ref> although in some species, such as some [[coucal]]s, the males invest more [[parental care]].<ref>{{cite journal | vauthors = Henshaw JM, Fromhage L, Jones AG | title = Sex roles and the evolution of parental care specialization | journal = Proceedings. Biological Sciences | volume = 286 | issue = 1909 | pages = 20191312 | date = August 2019 | pmid = 31455191 | pmc = 6732396 | doi = 10.1098/rspb.2019.1312 }}</ref> Females also tend to be more choosy for who they mate with,<ref>{{cite journal | vauthors = Brennan P | date = 2010 | title = Sexual Selection {{!}} Learn Science at Scitable | journal = Nature Education Knowledge | volume = 3 | issue = 10 | page = 79 |url= https://www.nature.com/scitable/knowledge/library/sexual-selection-13255240/|access-date=25 July 2021 |archive-date=9 October 2021|archive-url= https://web.archive.org/web/20211009163133/https://www.nature.com/scitable/knowledge/library/sexual-selection-13255240/|url-status=live}}</ref> such as most bird species.<ref>{{cite book| vauthors = Macedo RH, Manica LT | chapter = Sexual Selection and Mating Systems: Contributions from a Neotropical Passerine Model | veditors = Reboreda JC, Fiorini VD, Tuero DT |url={{GBurl|id=ItmUDwAAQBAJ|q=behavioral+ecology+choosy+female|p=75}}|title=Behavioral Ecology of Neotropical Birds |date=2019|publisher=Springer|isbn=978-3-030-14280-3|pages=75|language=en}}</ref> Males tend to be more competitive for mating than females.<ref name="Lehtonen-2016">{{cite journal | vauthors = Lehtonen J, Kokko H, Parker GA | title = What do isogamous organisms teach us about sex and the two sexes? | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 371 | issue = 1706 | date = October 2016 | pmid = 27619696 | pmc = 5031617 | doi = 10.1098/rstb.2015.0532 | author-link2 = Hanna Kokko | author-link3 = Geoff Parker }}</ref>