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{{Short description|Sex of an organism that produces ova}}
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[[File:Venus symbol.svg|thumb|The symbol of the Roman goddess [[Venus (mythology)|Venus]] is used to represent the female sex in biology.<ref name="Stearn-symbols">{{cite journal|last1=Stearn |first1=William T. |author-link=William T. Stearn |date=May 1962 |title=The Origin of the Male and Female Symbols of Biology |url=https://iapt-taxon.org/historic/Congress/IBC_1964/male_fem.pdf |journal=[[Taxon (journal)|Taxon]] |volume=11 |issue=4 |pages=109–113 |doi=10.2307/1217734 |issn=0040-0262 |jstor=1217734}}</ref>]]
An [[organism]]'s [[sex]] is '''female''' ([[Venus symbol|symbol]]: [[♀]]) if it produces the [[ovum]] (egg cell), the type of [[gamete]] (sex cell) that fuses with the [[male gamete]] (sperm cell) during [[sexual reproduction]].<ref>{{cite book |last1=Grzimek |first1=Bernhard |title=Grzimek's Animal Life Encyclopedia |date=2003 |publisher=Gale |isbn=978-0-7876-5362-0 |volume=1 |pages=16–17 |url=https://books.google.com/books?id=8GZvtQEACAAJ |language=en |quote=During sexual reproduction, each parent animal must form specialized cells known as gametes...In virtually all animals that reproduce sexually, the gametes occur in two morphologically distinct forms corresponding to male and female. These distinctions in form and structure are related to the specific functions of each gamete. The differences become apparent during the latter stages of spermatogenesis (for male gametes) and oogenesis (for female gametes)....After oogenetic meiosis, the morphological transformation of the female gamete generally includes development of a large oocyte that does not move around....The ambiguous term "egg" is often applied to oocytes and other fertilizable stages of female gametes....Spermatogenesis and oogenesis most often occur in different individual animals known as males and females respectively. |access-date=2020-07-09 |archive-date=2024-05-10 |archive-url=https://web.archive.org/web/20240510013251/https://books.google.com/books?id=8GZvtQEACAAJ |url-status=live }}</ref><ref name="Martin 2015" /><ref>{{Cite book|last1=Fusco|first1=Giuseppe|url=https://books.google.com/books?id=AKGsDwAAQBAJ&q=the+biology+of+reproduction+define+sex|title=The Biology of Reproduction|last2=Minelli|first2=Alessandro|date=2019-10-10|publisher=Cambridge University Press|isbn=978-1-108-49985-9|pages=111–113|language=en|access-date=2021-09-09|archive-date=2024-05-10|archive-url=https://web.archive.org/web/20240510013213/https://books.google.com/books?id=AKGsDwAAQBAJ&q=the+biology+of+reproduction+define+sex#v=snippet&q=the%20biology%20of%20reproduction%20define%20sex&f=false|url-status=live}}</ref>
A female has larger gametes than a [[male]]. Females and males are results of the [[anisogamous]] [[reproductive system|reproduction system]], wherein gametes are of different sizes (unlike [[isogamy]] where they are the same size). The exact mechanism of female gamete evolution remains unknown.
In species that have males and females, [[Sex-determination system|sex-determination]] may be based on either [[sex chromosomes]], or environmental conditions. Most female [[mammal]]s, including female [[human]]s, have two [[X chromosome]]s. Characteristics of organisms with a female sex vary between different species, having different [[female reproductive system]]s, with some species showing [[Secondary sex characteristic|characteristics secondary to the reproductive system]], as with [[mammary gland]]s in mammals.
In humans, the word ''female'' can also be used to refer to [[gender]] in the social sense of [[gender role]] or [[gender identity]].<ref name=palazzani>{{cite book |last1=Palazzani |first1=Laura |url=https://books.google.com/books?id=w8bbP6D7U2UC&pg=PA5 |title=Gender in Philosophy and Law |last2=Bailes |first2=Victoria |last3=Fella |first3=Marina |publisher=Dordrecht : Springer |year=2012 |isbn=9789400749917 |series=SpringerBriefs in law |page=v |quote='gender' means human gender, male/female gender}} (eBook)</ref><ref name="merriam1">{{Cite web |title=Definition of FEMALE |url=https://www.merriam-webster.com/dictionary/female |access-date=2023-03-07 |website=www.merriam-webster.com |language=en |archive-date=2023-03-07 |archive-url=https://web.archive.org/web/20230307162530/https://www.merriam-webster.com/dictionary/female |url-status=live }}</ref>
==Etymology and usage==
[[File:Beowulf - faemnan.jpg|thumb|"{{lang|ang|fæmnan}}", an [[Old English]] word for 'female']]
The word ''female'' comes from the Latin {{lang|la|femella}}, the diminutive form of {{lang|la|femina}}, meaning "[[woman]]", by way of the Old French ''femelle''.<ref name=":1">{{Cite book |last1=Fowler |first1=Henry W. |title=Fowler's Dictionary of Modern English Usage |last2=Butterfield |first2=Jeremy |date=2015 |publisher=Oxford University Press |isbn=978-0-19-966135-0 |edition=4th |___location=Oxford |chapter=female}}</ref> It is not etymologically related to the word ''[[male]]'', but in the late 14th century the English spelling was altered to parallel that of ''male''.<ref name=":1" /><ref name="Ayers">Donald M. Ayers, ''English Words from Latin and Greek Elements'', second edition (1986, University of Arizona Press), p. 113</ref> It has been used as both noun and adjective since the 14th century.<ref name=":1"/> Originally, from its first appearance in the 1300s, ''female'' exclusively referred to humans and always indicated that the speaker spoke of a woman or a girl.<ref name=":0">{{Cite web |title=Using 'Lady,' 'Woman,' and 'Female' to Modify Nouns |url=https://www.merriam-webster.com/words-at-play/lady-woman-female-usage |url-status=live |archive-url=https://web.archive.org/web/20220804103718/https://www.merriam-webster.com/words-at-play/lady-woman-female-usage |archive-date=2022-08-04 |access-date=2022-08-04 |website=Merriam–Webster |language=en}}</ref> A century later, the meaning was expanded to include non-human female organisms.<ref name=":0"/>
For several centuries, using the word ''female'' as a noun was considered more respectful than calling her a ''woman'' or a ''lady'' and was preferred for that reason;<ref name=":0"/> however, by 1895,<ref name=":1"/><ref>{{Cite magazine |last=Newton-Small |first=Jay |date=2016-04-19 |title=Why We Need to Reclaim the Word 'Female' |url=https://time.com/4300170/female-word/ |access-date=2024-05-10 |magazine=TIME |language=en |quote=Katherine Martin, head of U.S. dictionaries at Oxford University Press...cites the OED’s original entry for female in 1895, in which the editors described its usage as "now commonly avoided by good writers, exc. with contemptuous implication."}}</ref> the linguistic fashion had changed, and ''female'' was often considered disparaging, usually on the grounds that it grouped humans with other animals.<ref name=":1" /><ref>{{cite web |last=Brown |first=Kara |date=5 February 2015 |title=The Problem With Calling Women 'Females' |url=https://www.jezebel.com/the-problem-with-calling-women-females-1683808274 |url-status=live |archive-url=https://web.archive.org/web/20240507031927/https://www.jezebel.com/the-problem-with-calling-women-females-1683808274 |archive-date=7 May 2024 |access-date=9 May 2024 |website=[[Jezebel (website)|Jezebel]]}}</ref> In the 21st century, the noun ''female'' is primarily used to describe non-human animals, to refer to biologically female humans in an impersonal technical context (e.g., "Females were more likely than males to develop an autoimmune disease"), or to impartially include a range of people without reference to age (e.g., ''girls'') or social status (e.g., ''lady'').<ref name=":1" /> As an adjective, ''female'' is still used in some contexts, particularly when the sex of the person is relevant, such as [[Female athlete|''female athletes'']] or to distinguish a ''[[male nurse]]'' from a female one.<ref>{{Cite book |last1=Fowler |first1=H. W. |title=Fowler's Dictionary of Modern English Usage |last2=Butterfield |first2=Jeremy |date=2015 |publisher=Oxford University Press |isbn=978-0-19-966135-0 |edition=Fourth |___location=Oxford; New York, NY |chapter=female, feminine |quote=One talks of ''female athletes, characters'' (in fiction and so forth), ''friends, officers, patients, roles, students, workers, and of the female body, sexuality'', etc....Some people object to the use of ''female'' as an adjective, as in ''female police officer, female senator'', etc. Their objections are based either on the negative connotations of ''female'' as a noun, or on the argument that mentioning the sex of the office holder is automatically sexist, unless the sex of the person denoted is relevant in the context.}}</ref>
Biological sex is [[Sex and gender distinction|conceptually distinct]] from [[gender]],<ref>{{Cite web |title=Gender and Genetics |url=https://www.who.int/genomics/gender/en/ |archive-url=https://web.archive.org/web/20121111125721/http://www.who.int/genomics/gender/en/ |archive-date=November 11, 2012 |access-date=2020-07-31 |website=WHO}}</ref><ref>{{Cite web |title=Sex & Gender |url=https://orwh.od.nih.gov/sex-gender |url-status=dead |archive-url=https://web.archive.org/web/20200723154514/https://orwh.od.nih.gov/sex-gender |archive-date=2020-07-23 |access-date=2020-07-31 |website=Office of Research on Women's Health}}</ref> although they are often used interchangeably.<ref name=udry>{{cite journal |doi=10.2307/2061790 |first1=J. Richard |last1=Udry |date=November 1994 |title=The Nature of Gender |journal=Demography |volume=31 |issue=4 |pages=561–573 |pmid=7890091 |url=https://www.unc.edu/courses/2006fall/econ/586/001/Readings/Udry_Nature_Gender.pdf |jstor=2061790 |url-status=live |archive-url=http://archive.wikiwix.com/cache/20161211012757/https://www.unc.edu/courses/2006fall/econ/586/001/Readings/Udry_Nature_Gender.pdf |archive-date=2016-12-11 |doi-access=free }}</ref><ref name="haig">{{cite journal|first1=David |last1=Haig |author-link1=David Haig (biologist) |date=April 2004 |title=The Inexorable Rise of Gender and the Decline of Sex: Social Change in Academic Titles, 1945–2001 |journal=Archives of Sexual Behavior |volume=33 |issue=2 |pages=87–96 |pmid=15146141 |doi=10.1023/B:ASEB.0000014323.56281.0d |url=http://www.oeb.harvard.edu/faculty/haig/publications_files/04inexorablerise.pdf |archive-url=https://web.archive.org/web/20110525090802/http://www.oeb.harvard.edu/faculty/haig/Publications_files/04InexorableRise.pdf |archive-date=25 May 2011 |url-status=dead |citeseerx=10.1.1.359.9143 |s2cid=7005542 }}</ref> The adjective ''female'' can describe a person's sex or [[gender identity]].<ref name="merriam1"/>
The word can also refer to the [[gender of connectors and fasteners|shape of connectors and fasteners]], such as screws, electrical pins, and technical equipment. Under this convention, sockets and receptacles are called ''female,'' and the corresponding plugs ''male''.<ref>J. Richard Johnson, ''How to Build Electronic Equipment'' (1962), p. 167: "To minimize confusion, the connector portions with projecting prongs are referred to as the 'male' portion, and the sockets as the 'female' portion."</ref><ref>Richard Ferncase, ''Film and Video Lighting Terms and Concepts'' (2013), p. 96: "female[:] Refers to a socket type connector, which must receive a male connector"</ref>
==Defining characteristics==
Females produce [[ovum|ova]], the larger gametes in a [[heterogamous]] [[reproduction system]], while the smaller and usually [[Motility|motile]] gametes, the [[spermatozoa]], are produced by males.<ref name="Martin 2015">{{cite book|last1=Martin|first1=Elizabeth|url=https://books.google.com/books?id=gMf9CAAAQBAJ|title=A Dictionary of Biology|last2=Hine|first2=Robert|date=2015|publisher=Oxford University Press|isbn=978-0-19-871437-8|page=222|language=en|quote=Female 1. Denoting the gamete (sex cell) that, during sexual reproduction, fuses with a male gamete in the process of fertilization. Female gametes are generally larger than the male gametes and are usually immotile (see Oosphere; Ovum). 2. (Denoting) an individual organism whose reproductive organs produce only female gametes.|access-date=2020-07-12|archive-date=2023-01-14|archive-url=https://web.archive.org/web/20230114185312/https://books.google.com/books?id=gMf9CAAAQBAJ|url-status=live}}</ref><ref>David E. Sadava, H. Craig Heller, William K. Purves, ''Life: The Science of Biology'' (2008), p. 899</ref> Generally, a female cannot [[sexual reproduction|reproduce sexually]] without access to the gametes of a male, and vice versa,<!--[citation to be added]--> but in some species females can reproduce by themselves [[asexual reproduction|asexually]], for example via [[parthenogenesis]].<ref>Franz Engelmann, G. A. Kerkut, ''The Physiology of Insect Reproduction'' (2015), p. 29</ref>
Patterns of sexual reproduction include:
* [[Isogamy|Isogamous]] species with two or more [[mating type]]s with gametes of identical form and behavior (but different at the molecular level),
* [[Anisogamy|Anisogamous]] species with [[gamete]]s of male and female types,
* [[Oogamy|Oogamous]] species, which include humans, in which the female gamete is much larger than the male and has no ability to [[Motion (physics)|move]]. Oogamy is a form of [[anisogamy]].<ref name="Kumar-201922">{{Cite encyclopedia|entry=Anisogamy |encyclopedia=Encyclopedia of Animal Cognition and Behavior|publisher=Springer International |___location=Cham |date=2019 |pages=1–5 |doi=10.1007/978-3-319-47829-6_340-1 |isbn=978-3-319-47829-6 |vauthors=Kumar R, Meena M, Swapnil P|title=Anisogamy |veditors=Vonk J, Shackelford T}}</ref> There is an argument that this pattern was driven by the physical constraints on the mechanisms by which two gametes get together as required for [[sexual reproduction]].<ref>Dusenbery, David B. (2009). ''Living at Micro Scale'', Chapter 20. Harvard University Press, Cambridge, Massachusetts {{ISBN|978-0-674-03116-6}}.</ref>
Other than the defining difference in the type of gamete produced, differences between males and females in one lineage cannot always be predicted by differences in another. The concept is not limited to animals; egg cells are produced by [[chytrid]]s, [[diatom]]s, [[water mould]]s and [[plant|land plants]], among others. In land plants, ''female'' and ''male'' designate not only the egg- and sperm-producing organisms and structures, but also the structures of the [[sporophyte]]s that give rise to male and [[female plant]]s.{{citation needed|date=March 2017}}
== Females across species ==
Species that are divided into females and males are classified as [[Gonochorism|gonochoric]] in animals, as [[Dioecy|dioecious]] in [[seed plants]]<ref>{{Cite book|last1=Fusco|first1=Giuseppe|url=https://books.google.com/books?id=AKGsDwAAQBAJ&q=gonochorism+biology+of+reproduction|title=The Biology of Reproduction|last2=Minelli|first2=Alessandro|date=2019-10-10|publisher=Cambridge University Press|isbn=978-1-108-49985-9|pages=115–116|language=en|access-date=2021-08-17|archive-date=2024-05-10|archive-url=https://web.archive.org/web/20240510013302/https://books.google.com/books?id=AKGsDwAAQBAJ&q=gonochorism+biology+of+reproduction#v=snippet&q=gonochorism%20biology%20of%20reproduction&f=false|url-status=live}}</ref> and as [[dioicous]] in [[cryptogam]]s.<ref name=ShawGoffinet>{{cite book |editor=Shaw AJ & Goffinet B |date=August 2000 |author=Buck WR & Goffinet B |title=Bryophyte Biology |chapter=Morphology and classification of mosses |___location=New York |publisher=Cambridge University Press |isbn=978-0-521-66794-4}}</ref>{{rp|82}}
In some species, female and hermaphrodite individuals may coexist, a [[sexual system]] termed [[gynodioecy]].<ref name="Bachtrog-2014">{{cite journal|display-authors=6|vauthors=Bachtrog D, Mank JE, Peichel CL, Kirkpatrick M, Otto SP, Ashman TL, Hahn MW, Kitano J, Mayrose I, Ming R, Perrin N, Ross L, Valenzuela N, Vamosi JC|date=July 2014|title=Sex determination: why so many ways of doing it?|journal=PLOS Biology|volume=12|issue=7|pages=e1001899|doi=10.1371/journal.pbio.1001899|pmc=4077654|pmid=24983465 |doi-access=free }}</ref> In a few species, female individuals coexist with males and [[hermaphrodite]]s; this sexual system is called [[trioecy]]. In ''[[Thor manningi]]'' (a species of shrimp), females coexist with males and [[protandrous hermaphrodite]]s.<ref>{{Cite book|last1=Fusco|first1=Giuseppe|url=https://books.google.com/books?id=AKGsDwAAQBAJ&q=trioecy&pg=PA133|title=The Biology of Reproduction|last2=Minelli|first2=Alessandro|date=2019-10-10|publisher=Cambridge University Press|isbn=978-1-108-49985-9|pages=133–135|language=en|access-date=2021-08-17|archive-date=2024-05-10|archive-url=https://web.archive.org/web/20240510013252/https://books.google.com/books?id=AKGsDwAAQBAJ&q=trioecy&pg=PA133#v=snippet&q=trioecy&f=false|url-status=live}}</ref>
===Mammalian female===
[[File:Anterior view of human female and male, with labels 2.png|thumb|Photograph of an adult female human, with an adult [[male]] for comparison. (Both models have partially shaved body hair to show anatomy, i.e., clean-shaven pubic regions.)]]
A distinguishing characteristic of the [[class (biology)|class]] ''Mammalia'' is the presence of [[mammary gland]]s. Mammary glands are modified sweat glands that produce milk, which is used to feed the young for some time after birth. Only mammals [[Lactation|produce milk]]. Mammary glands are [[Breast#Other suggested functions|obvious]] in [[humans]], because the female human body stores large amounts of fatty tissue near the nipples, resulting in prominent [[breast]]s. Mammary glands are present in all mammals, although they are normally redundant in males of the species.<ref>{{cite web|last1=Swaminathan|first1=Nikhil|title=Strange but True: Males Can Lactate|url=https://www.scientificamerican.com/article/strange-but-true-males-can-lactate/|website=Scientific American|language=en|access-date=2017-10-06|archive-date=2019-12-23|archive-url=https://web.archive.org/web/20191223174929/https://www.scientificamerican.com/article/strange-but-true-males-can-lactate/|url-status=live}}</ref>
Most mammalian females have two copies of the [[X chromosome]], while males have only one X and one smaller [[Y chromosome]]; some mammals, such as the [[platypus]], have different combinations.<ref>Adrian T. Sumner, ''Chromosomes: Organization and Function'' (2008), pp. 97-98</ref><ref>Benjamin A. Pierce, ''Genetics: A Conceptual Approach'' (2012), p. 73</ref> One of the female's X chromosomes is [[X-inactivation|randomly inactivated]] in each cell of placental mammals while the paternally derived X is inactivated in marsupials. In birds and some reptiles, by contrast, it is the female which is [[heterozygous]] and carries a Z and a W chromosome while the male carries two Z chromosomes. In mammals, females can have [[Trisomy X|XXX]] or [[Turner syndrome|X]].<ref>John R. McCarrey, Ursula K. Abbott, "Sex Determination in Animals", in ''Advances in Genetics'' (1979), volume 20, pages 219-220</ref><ref name="Hake-2021">{{Cite journal |last1=Hake |first1=Laura |last2=O'Connor |first2=Clare |title=Genetic Mechanisms of Sex Determination |journal=Nature Education |volume=1 |issue=1 |page=25 |url=https://www.nature.com/scitable/topicpage/genetic-mechanisms-of-sex-determination-314/ |access-date=2021-04-13 |language=en |archive-date=2017-08-19 |archive-url=https://web.archive.org/web/20170819121941/http://www.nature.com/scitable/topicpage/genetic-mechanisms-of-sex-determination-314 |url-status=live }}</ref>
Mammalian females [[Viviparity|bear live young]], with the exception of [[monotreme]] females, which lay eggs.<ref>Terry Vaughan, James Ryan, Nicholas Czaplewski, ''Mammalogy'' (2011), pp. 391, 412</ref> Some non-mammalian species, such as [[guppy|guppies]], have analogous reproductive structures; and some other non-mammals, such as some [[shark]]s, also bear live young.<ref>Quentin Bone, Richard Moore, ''Biology of Fishes'' (2008), page 234</ref>
Following experiments by French endocrinologist Alfred Jost in the 1940s, it is widely believed that the female is the default sex in mammalian sexual determination. However, this idea was called into question by a 2017 study.<ref name="Johnson Hopkins Medicine">{{cite web|url=https://biomedicalodyssey.blogs.hopkinsmedicine.org/2017/09/its-hard-work-being-a-boy-and-it-turns-out-a-girl/|date=15 Dec 2024|title=It’s Hard Work Being a Boy (and, It Turns Out, a Girl)}}</ref><ref name="Science">{{cite web|url=https://www.science.org/doi/10.1126/science.aai9136|date=15 Dec 2024|title=Elimination of the male reproductive tract in the female embryo is promoted by COUP-TFII in mice}}</ref>
==Sex determination==
{{
The sex of a particular organism may be determined by genetic or environmental factors, or may naturally change during the course of an organism's life.<ref name="Bachtrog-2014" />
===Genetic determination===
===Environmental determination===
The young of some species develop into one sex or the other depending on local environmental conditions, e.g. the sex of crocodilians is influenced by the temperature of their eggs. Other species (such as the [[goby]]) can transform, as adults, from one sex to the other in response to local reproductive conditions (such as a brief shortage of males).<ref>{{Cite journal|last1=Gemmell|first1=Neil J.|last2=Muncaster|first2=Simon|last3=Liu|first3=Hui|last4=Todd|first4=Erica V.|date=2016|title=Bending Genders: The Biology of Natural Sex Change in Fish|journal=Sexual Development|language=english|volume=10|issue=5–6|pages=223–241|doi=10.1159/000449297|issn=1661-5425|pmid=27820936|doi-access=free|hdl=10536/DRO/DU:30153787|hdl-access=free}}</ref>
In
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{{See also|Evolution of sexual reproduction|Sex#Evolution of sex}}The question of how females evolved is mainly a question of why males evolved. The first organisms reproduced asexually, usually via [[binary fission]], wherein a [[Cell (biology)|cell]] splits itself in half. From a strict numbers perspective, a species that is half males/half females can produce half the offspring an asexual population can, because only the females are having offspring. Being male can also carry significant costs, such as in flashy sexual displays in animals (such as big antlers or colorful feathers), or needing to produce an outsized amount of pollen as a plant in order to get a chance to fertilize a female. Yet despite the costs of being male, there must be some advantage to the process.<ref name="Togashi-2011" />
The advantages are explained by the [[Anisogamy#Evolution|evolution of anisogamy]], which led to the evolution of male and female function.<ref name="Bachtrog-20142">{{cite journal |vauthors=Bachtrog D, [[Judith Mank|Mank JE]], Peichel CL, [[Mark Kirkpatrick|Kirkpatrick M]], [[Sarah Otto|Otto SP]], Ashman TL, Hahn MW, Kitano J, Mayrose I, Ming R, Perrin N, Ross L, Valenzuela N, Vamosi JC |date=July 2014 |title=Sex determination: why so many ways of doing it? |journal=PLOS Biology |volume=12 |issue=7 |pages=e1001899 |doi=10.1371/journal.pbio.1001899 |pmc=4077654 |pmid=24983465 |doi-access=free}}</ref> Before the evolution of anisogamy, [[mating type]]s in a species were [[Isogamy|isogamous]]: the same size and both could move, catalogued only as "+" or "-" types.<ref name=Sawada>{{Cite book|last1=Sawada|first1=Hitoshi|url=https://books.google.com/books?id=Adm6BQAAQBAJ&q=isogamy+mating+types|title=Sexual Reproduction in Animals and Plants|last2=Inoue|first2=Naokazu|last3=Iwano|first3=Megumi|date=2014|publisher=Springer|isbn=978-4-431-54589-7|language=en|access-date=2021-09-09|archive-date=2024-04-04|archive-url=https://web.archive.org/web/20240404062136/https://books.google.com/books?id=Adm6BQAAQBAJ&q=isogamy+mating+types#v=snippet&q=isogamy%20mating%20types&f=false|url-status=live}}</ref>{{rp|216}} In anisogamy, the mating cells are called gametes. The female gamete is larger than the male gamete, and usually immotile.<ref name="Kumar-20192">{{Cite encyclopedia |entry=Anisogamy |encyclopedia=Encyclopedia of Animal Cognition and Behavior |publisher=Springer International |___location=Cham |date=2019 |pages=1–5 |doi=10.1007/978-3-319-47829-6_340-1 |isbn=978-3-319-47829-6 |vauthors=Kumar R, Meena M, Swapnil P|title=Anisogamy |veditors=Vonk J, Shackelford T}}</ref> Anisogamy remains poorly understood, as there is no fossil record of its emergence. Numerous theories exist as to why anisogamy emerged. Many share a common thread, in that larger female gametes are more likely to survive, and that smaller male gametes are more likely to find other gametes because they can travel faster. Current models often fail to account for why isogamy remains in a few species.<ref name="Togashi-2011">{{Cite book|last1=Togashi|first1=Tatsuya|url=https://books.google.com/books?id=5eOvRTIuLXMC&dq=Title%3A+The+Evolution+of+Anisogamy+%3A+A+Fundamental+Phenomenon+Underlying+Sexual+Selection&pg=PR5|title=The Evolution of Anisogamy: A Fundamental Phenomenon Underlying Sexual Selection|last2=Cox|first2=Paul Alan|date=2011-04-14|publisher=Cambridge University Press|isbn=978-1-139-50082-1|pages=1–15|language=en|access-date=2021-11-27|archive-date=2024-05-10|archive-url=https://web.archive.org/web/20240510013300/https://books.google.com/books?id=5eOvRTIuLXMC&dq=Title%3A+The+Evolution+of+Anisogamy+%3A+A+Fundamental+Phenomenon+Underlying+Sexual+Selection&pg=PR5#v=onepage&q=Title%3A%20The%20Evolution%20of%20Anisogamy%20%3A%20A%20Fundamental%20Phenomenon%20Underlying%20Sexual%20Selection&f=false|url-status=live}}</ref> Anisogamy appears to have evolved multiple times from isogamy; for example female [[Volvocales]] (a type of green algae) evolved from the plus [[mating type]].<ref name=Sawada />{{rp|222}} Although sexual evolution emerged at least 1.2 billion years ago, the lack of anisogamous fossil records make it hard to pinpoint when females evolved.<ref name="PB-2000">{{cite journal|last=Butterfield|first=Nicholas J.|date=2000|title=Bangiomorpha pubescens n. gen., n. sp.: implications for the evolution of sex, multicellularity, and the Mesoproterozoic/Neoproterozoic radiation of eukaryotes|url=http://mr.crossref.org/iPage?doi=10.1666%2F0094-8373%282000%29026%3C0386%3ABPNGNS%3E2.0.CO%3B2|journal=[[Paleobiology (journal)|Paleobiology]]|volume=26|issue=3|page=386|doi=10.1666/0094-8373(2000)026<0386:BPNGNS>2.0.CO;2|bibcode=2000Pbio...26..386B|s2cid=36648568|access-date=12 April 2021|archive-date=1 February 2022|archive-url=https://web.archive.org/web/20220201160801/http://mr.crossref.org/iPage?doi=10.1666%2F0094-8373(2000)026%3C0386%3ABPNGNS%3E2.0.CO%3B2|url-status=live|url-access=subscription}}</ref>
Female [[sex organ]]s (genitalia, in animals) have an extreme range of variation among species and even within species. The evolution of female genitalia remains poorly understood compared to male genitalia, reflecting a now-outdated belief that female genitalia are less varied than male genitalia, and thus less useful to study. The difficulty of reaching female genitalia has also complicated their study. New 3D technology has made female genital study simpler. Genitalia evolve very quickly. There are three main hypotheses as to what impacts female genital evolution: lock-and-key (genitals must fit together), [[cryptic female choice]] (females affect whether males can fertilize them), and [[sexual conflict]] (a sort of sexual arms race). There is also a hypothesis that female genital evolution is the result of [[pleiotropy]], i.e. unrelated genes that are affected by environmental conditions like low food also affect genitals. This hypothesis is unlikely to apply to a significant number of species, but [[natural selection]] in general has some role in female genital evolution.<ref>{{Cite journal|last1=Sloan|first1=Nadia S.|last2=Simmons|first2=Leigh W.|date=2019|title=The evolution of female genitalia|journal=Journal of Evolutionary Biology|volume=32|issue=9|pages=882–899|doi=10.1111/jeb.13503|pmid=31267594|issn=1420-9101|doi-access=free}}</ref>
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{{Main|Gender symbol|Venus symbol}}
The symbol ♀ ([[Unicode]]: U+2640 [[Alt codes]]: Alt+12), a circle with a small cross underneath, is commonly used to represent females. [[Joseph Justus Scaliger]] once speculated that the symbol was associated with [[Venus (goddess)|Venus, goddess of beauty]], because it resembles a bronze mirror with a handle,<ref>{{Citation|last=Taylor|first=Robert B.|title=White Coat Tales|date=2016|pages=293–310|chapter=Now and Future Tales|publisher=Springer International Publishing|doi=10.1007/978-3-319-29055-3_12|isbn=978-3-319-29053-9}}</ref> but modern scholars consider that fanciful, and the most established view is that the female and male symbols derive from contractions in Greek script of the Greek names of the planets Thouros (Mars) and Phosphoros (Venus).<ref name="Stearn">{{cite journal|last=Stearn|first=William T.|date=May 1962|title=The Origin of the Male and Female Symbols of Biology|journal=Taxon|volume=11|issue=4|pages=109–113|doi=10.2307/1217734|jstor=1217734|quote=The origin of these symbols has long been of interest to scholars. Probably none now accepts the interpretation of Scaliger that {{char|♂}} represents the shield and spear of Mars and {{char|♀}} Venus's looking glass.|s2cid=87030547}}</ref><ref>G D Schott, ''Sex, drugs, and rock and roll: Sex symbols ancient and modern: their origins and iconography on the pedigree'', ''BMJ'' 2005;331:1509-1510 (24 December), {{doi|10.1136/bmj.331.7531.1509}}</ref>
==See also==
{{Wiktionary}}
{{commons category|Females}}
{{Portal|Human sexuality|Feminism}}
* [[Girl]]
* [[
* [[Femininity]]
* [[Lady]]
* [[Woman]]
==References==
{{reflist}}
{{Sex (biology)}}
{{Sexual identities}}
{{Authority control}}
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