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The symbol of the Roman goddess Venus is used to represent the female sex in biology. Venus symbol.svg
The symbol of the Roman goddess Venus is used to represent the female sex in biology.

An organism's sex is female (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. [2] [3] [4]


A female has larger gametes than a male. Females and males are results of the anisogamous 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 may be based on either sex chromosomes, or environmental conditions. Most female mammals, including female humans, have two X chromosomes. Female characteristics vary between different species, with some species having pronounced secondary female sex characteristics, such as the presence of pronounced mammary glands 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. [5] [6]

Etymology and usage

", an Old English word for 'female' Beowulf - faemnan.jpg
"fæmnan", an Old English word for 'female'

The word female comes from the Latin femella, the diminutive form of femina, meaning "woman". 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. [7] [8] Female is also used as a noun meaning "a female organism", though describing women as females is often considered disparaging, as it makes no distinction between other animals and humans. [9] [10]

Biological sex is conceptually distinct from gender, [11] [12] although they are often used interchangeably. [13] [14] The adjective female can describe a person's sex or gender identity. [6]

The word can also refer to the 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. [15] [16]

Defining characteristics

Females produce ova, the larger gametes in a heterogamous reproduction system, while the smaller and usually motile gametes, the spermatozoa, are produced by males. [3] [17] Generally, a female cannot reproduce sexually without access to the gametes of a male, and vice versa, but in some species females can reproduce by themselves asexually, for example via parthenogenesis. [18]

Patterns of sexual reproduction include:

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 chytrids, diatoms, water moulds and 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 sporophytes that give rise to male and female plants.[ citation needed ]

Females across species

Species that are divided into females and males are classified as gonochoric in animals, as dioecious in seed plants [21] and as dioicous in cryptogams. [22] :82

In some species, female and hermaphrodite individuals may coexist, a sexual system termed gynodioecy. [23] In a few species, female individuals coexist with males and simultaneous hermaphrodites; this sexual system is called trioecy. [24] In Thor manningi (a species of shrimp), females coexist with males and protandrous hermaphrodites. [25]

Mammalian female

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.) Anterior view of human female and male, with labels 2.png
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 Mammalia is the presence of mammary glands. Mammary glands are modified sweat glands that produce milk, which is used to feed the young for some time after birth. Only mammals produce milk. Mammary glands are obvious in humans, because the female human body stores large amounts of fatty tissue near the nipples, resulting in prominent breasts. Mammary glands are present in all mammals, although they are normally redundant in males of the species. [26]

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. [27] [28] One of the female's X chromosomes is 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 XXX or X. [29] [30]

Mammalian females bear live young, with the exception of monotreme females, which lay eggs. [31] Some non-mammalian species, such as guppies, have analogous reproductive structures; and some other non-mammals, such as some sharks, also bear live young. [32]

In sex determination for mammals, female is the default sex, while in the poplar genus Populus the default is male. [33]

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. [23]

Genetic determination

The sex of most mammals, including humans, is genetically determined by the XY sex-determination system where females have XX (as opposed to XY in males) sex chromosomes. It is also possible in a variety of species, including humans, to have other karyotypes. During reproduction, the male contributes either an X sperm or a Y sperm, while the female always contributes an X egg. A Y sperm and an X egg produce a male, while an X sperm and an X egg produce a female. The ZW sex-determination system, where females have ZW (as opposed to ZZ in males) sex chromosomes, is found in birds, reptiles and some insects and other organisms. [23]

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). [34]


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 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 despites the costs of being male, there must be some advantage to the process. [35]

The advantages are explained by the evolution of anisogamy, which led to the evolution of male and female function. [36] Before the evolution of anisogamy, mating types in a species were isogamous: the same size and both could move, catalogued only as "+" or "-" types. [37] :216 In anisogamy, the mating cells are called gametes. The female gamete is larger than the male gamete, and usually immotile. [38] 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. [35] Anisogamy appears to have evolved multiple times from isogamy; for example female Volvocales (a type of green algae) evolved from the plus mating type. [37] :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. [39]

Female sex organs (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. [40]


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 of beauty, because it resembles a bronze mirror with a handle, [41] 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). [42] [43]

See also

Related Research Articles

<span class="mw-page-title-main">Gamete</span> A haploid sex cell

A gamete is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. The name gamete was introduced by the German cytologist Eduard Strasburger.

<span class="mw-page-title-main">Reproduction</span> Biological process by which new organisms are generated from one or more parent organisms

Reproduction is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. There are two forms of reproduction: asexual and sexual.

<span class="mw-page-title-main">Sex</span> Trait that determines an organisms sexually reproductive function

Sex is the trait that determines whether a sexually reproducing organism produces male or female gametes. During sexual reproduction, a male and a female gamete fuse to form a zygote, which develops into an offspring that inherits traits from each parent. By convention, organisms that produce smaller, more mobile gametes are called male, while organisms that produce produce larger, non-mobile gametes are called female. An organism that produces both types of gamete is hermaphrodite.

<span class="mw-page-title-main">Sex organ</span> Biological part involved in sexual reproduction

A sex organ, also known as a reproductive organ, is a part of an organism that is involved in sexual reproduction. Sex organs constitute the primary sex characteristics of an organism. Sex organs are responsible for producing and transporting gametes, as well as facilitating fertilization and supporting the development and birth of offspring. Sex organs are found in many species of animals and plants, with their features varying depending on the species.

<span class="mw-page-title-main">Fertilisation</span> Union of gametes of opposite sexes during the process of sexual reproduction to form a zygote

Fertilisation or fertilization, also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a zygote and initiate its development into a new individual organism or offspring. While processes such as insemination or pollination, which happen before the fusion of gametes, are also sometimes informally referred to as fertilisation, these are technically separate processes. The cycle of fertilisation and development of new individuals is called sexual reproduction. During double fertilisation in angiosperms, the haploid male gamete combines with two haploid polar nuclei to form a triploid primary endosperm nucleus by the process of vegetative fertilisation.

<span class="mw-page-title-main">XY sex-determination system</span> Method of determining sex

The XY sex-determination system is a sex-determination system used to classify many mammals, including humans, some insects (Drosophila), some snakes, some fish (guppies), and some plants. In this system, the sex of an individual is determined by a pair of sex chromosomes. In most cases, females have two of the same kind of sex chromosome (XX), and are called the homogametic sex. Males have two different kinds of sex chromosomes (XY), and are called the heterogametic sex.

<span class="mw-page-title-main">Sex-determination system</span> Biological system that determines the development of an organisms sex

A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most organisms that create their offspring using sexual reproduction have two common sexes and a few less common intersex variations.

<span class="mw-page-title-main">Egg cell</span> Female reproductive cell in most anisogamous organisms

The egg cell or ovum is the female reproductive cell, or gamete, in most anisogamous organisms. The term is used when the female gamete is not capable of movement (non-motile). If the male gamete (sperm) is capable of movement, the type of sexual reproduction is also classified as oogamous. A nonmotile female gamete formed in the oogonium of some algae, fungi, oomycetes, or bryophytes is an oosphere. When fertilized, the oosphere becomes the oospore.

<span class="mw-page-title-main">Sexual differentiation</span> Embryonic development of sex differences

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<span class="mw-page-title-main">Anisogamy</span> Sexual reproduction involving a large, female gamete and a small, male gamete

Anisogamy is a form of sexual reproduction that involves the union or fusion of two gametes that differ in size and/or form. The smaller gamete is male, a sperm cell, whereas the larger gamete is female, typically an egg cell. Anisogamy is predominant among multicellular organisms. In both plants and animals gamete size difference is the fundamental difference between females and males.

<span class="mw-page-title-main">Isogamy</span> Sexual reproduction form involving gametes of the same size

Isogamy is a form of sexual reproduction that involves gametes of the same morphology, and is found in most unicellular eukaryotes. Because both gametes look alike, they generally cannot be classified as male or female. Instead, organisms undergoing isogamy are said to have different mating types, most commonly noted as "+" and "−" strains.

Reproductive biology includes both sexual and asexual reproduction.

<span class="mw-page-title-main">Male</span> Sex of an organism which produces sperm

Male is the sex of an organism that produces the gamete known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilisation. A male organism cannot reproduce sexually without access to at least one ovum from a female, but some organisms can reproduce both sexually and asexually. Most male mammals, including male humans, have a Y chromosome, which codes for the production of larger amounts of testosterone to develop male reproductive organs.

<span class="mw-page-title-main">Oogamy</span> Form of sexual reproduction

Oogamy is a form of anisogamy where the gametes differ in both size and form. In oogamy the large female gamete is immotile, while the small male gamete is mobile. Oogamy is a common form of anisogamy, with almost all animals and land plants being oogamous.

<span class="mw-page-title-main">XO sex-determination system</span> Biological system that determines the sex of offspring

The XO sex-determination system is a system that some species of insects, arachnids, and mammals use to determine the sex of offspring. In this system, there is only one sex chromosome, referred to as X. Males only have one X chromosome (XO), while females have two (XX). The letter O signifies the lack of a Y chromosome. Maternal gametes always contain an X chromosome, so the sex of the animals' offspring depends on whether a sex chromosome is present in the male gamete. Its sperm normally contains either one X chromosome or no sex chromosomes at all.

<span class="mw-page-title-main">Hermaphrodite</span> Sexually reproducing organism that produces both male and female gametes

A hermaphrodite is a sexually reproducing organism that produces both male and female gametes. Animal species in which individuals are of different sexes, either male or female but not both, are gonochoric, which is the opposite of hermaphroditic.

The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are also important accessories to the reproductive system. Unlike most organ systems, the sexes of differentiated species often have significant differences. These differences allow for a combination of genetic material between two individuals, which allows for the possibility of greater genetic fitness of the offspring.

<span class="mw-page-title-main">Sexual reproduction</span> Biological process

Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete with a single set of chromosomes combines with another gamete to produce a zygote that develops into an organism composed of cells with two sets of chromosomes (diploid). This is typical in animals, though the number of chromosome sets and how that number changes in sexual reproduction varies, especially among plants, fungi, and other eukaryotes.

<span class="mw-page-title-main">Mammalian reproduction</span> Most mammals are viviparous, giving birth to live young

Most mammals are viviparous, giving birth to live young. However, the five species of monotreme, the platypuses and the echidnas, lay eggs. The monotremes have a sex determination system different from that of most other mammals. In particular, the sex chromosomes of a platypus are more like those of a chicken than those of a therian mammal.


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