Male
|
The shield and spear of the Roman God Mars are often used to represent the male sex |
In
heterogamous species,
male is the
sex of an
organism, or of a part of an organism, which typically produces smaller, mobile
gametes (
spermatozoa) that are able to
fertilise female gametes (
ova). A male individual cannot reproduce
sexually without access to the gametes of a female.
There is no single
genetic sex-determination system which controls sex differences in different species. The existence of two sexes seems to have
evolved multiple times
independently in different
evolutionary lineages. 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 of male/female
dimorphism between individuals or reproductive organs is not limited to
animals; male gametes are produced by
chytrids,
diatoms, and land
plants, among others. In land plants,
female and
male designate not only the female and male gamete-producing organisms and structures, but also the structures of the
sporophytes that give rise to male and female plants.
In those species with separate sexes, males may differ from females in ways other than production of spermatozoa. Males are generally smaller than females in seed plants (the
pollen grain is the male plant) and many fishes and birds, but larger in many mammals, including humans. In birds, the male often exhibits a colourful
plumage which is used to attract females.
The sex of a particular organism may be determined by a number of factors. These may be genetic or environmental, or may naturally change during the course of an organism's life. 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.
Genetic determination
Most
mammals, including
humans, are genetically determined as such by the
XY sex-determination system where males have an XY (as opposed to XX) sex
chromosome. During
reproduction, a male can give either an X sperm or a Y sperm, while a female can only give an X egg. A Y sperm and an X egg produce a
boy, while an X sperm and an X egg produce a
girl. The
ZW sex-determination system, where males have a ZZ (as opposed to ZW) sex chromosome may be found in
birds and some
insects and other organisms. 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.
Environmental determination
In some species of reptiles, including
alligators, sex is determined by the temperature at which the egg is incubated. Other species, such as some
snails, practice sex change: adults start out male, then become female. In tropical
clown fish, the dominant individual in a group becomes female while the other ones are male.
In some
arthropods, sex is determined by infection.
Bacteria of the genus
Wolbachia alter their sexuality; some species consist entirely of ZZ individuals, with sex determined by the presence of
Wolbachia.
All males, regardless of independent origin, kingdom, or other
phylogenetic subdivision, share at least the anatomy to produce male gametes. Some have sophisticated
organs and
organ systems designed to produce, dispense, and deliver the gamete to a location suitable for ovum fertilisation.
Even where structures and cell types have arisen independently, "
sperm" is ordinarily used to refer to the male gamete. Among animals that undergo
internal fertilization, "
penis" is often used to refer to an organ inserted into the female for
insemination.
A common
symbol used to represent the male gender is the
Mars symbol,
♂ (
Unicode: U+2642)—a circle with an arrow pointing
northeast. This is a stylized representation of the
Roman god Mars' shield and spear.
*
Female*
Man and
boy, male
humans
*
Sex*
Sex-determination system*
Sexual dimorphism*
Animal husbandry*
Hermaphrodite
