The concept is not limited to animals; egg cells are produced by chytrids , diatoms , water moulds and land plants , among others. It is not etymologically related to the word male, but in the late 14th century the spelling was altered in English to parallel the spelling of male. 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. The ZW sex-determination system , where males have ZZ as opposed to ZW sex chromosomes, is found in birds, reptiles and some insects and other organisms. These abbreviations were contracted into the modern symbols. Although most species with male and female sexes have individuals that are either male or female, hermaphroditic animals have both male and female reproductive organs.
According to Schott,  the most established view is that the male and female symbols "are derived from contractions in Greek script of the Greek names of these planets, namely Thouros Mars and Phosphoros Venus. Some non-mammalian species, such as guppies , have analogous reproductive structures; and some other non-mammals, such as sharks , whose eggs hatch inside their bodies, also have the appearance of bearing live young. These may be genetic or environmental, or may naturally change during the course of an organism's life. Mammary glands are present in all mammals, although they are seldom used by the males of the species. 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. A female individual cannot reproduce sexually without access to the gametes of a male, and vice versa. The ZW sex-determination system , where males have ZZ as opposed to ZW sex chromosomes, is found in birds, reptiles and some insects and other organisms. An example of asexual reproduction that some female species can perform is parthenogenesis. However, these conditions frequently result in sterility. In birds and some reptiles, by contrast, it is the female which is heterozygous and carries a Z and a W chromosome whilst the male carries two Z chromosomes. Sex-determination system The sex of a particular organism may be determined by a number of factors. 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. Oogamy is a form of anisogamy. 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. There is no single genetic mechanism behind sex differences in different species and the existence of two sexes seems to have evolved multiple times independently in different evolutionary lineages. The concept is not limited to animals; egg cells are produced by chytrids , diatoms , water moulds and land plants , among others. These abbreviations were contracted into the modern symbols. The mammary glands are modified sweat glands that produce milk, which is used to feed the young for some time after birth. During reproduction , the male contributes either an X sperm or a Y sperm, while the female always contributes an X egg. Some organisms can also reproduce by themselves in a process known as asexual reproduction. Only mammals produce milk. Wikimedia Commons has media related to Females. Although most species with male and female sexes have individuals that are either male or female, hermaphroditic animals have both male and female reproductive organs. Members of Hymenoptera , such as ants and bees, are determined by haplodiploidy , where most males are haploid and females and some sterile males are diploid. A distinguishing characteristic of the class Mammalia is the presence of mammary glands. These derivations have been traced by Renkama  who illustrated how Greek letters can be transformed into the graphic male and female symbols still recognised today. To compensate for the difference in size, 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.
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