Male

Male is one of two sexes in sexually reproducing organisms. A male is defined as an organism that produces small, mobile gametes—a gamete being a reproductive cell that fuses with another to form an offspring. In animals, this gamete is called a spermatozoon. By contrast, a female produces a large, relatively immobile gamete, which is the egg.

The definition of male is based on gamete size (anisogamy), not on external appearance, characteristics, or social role. The term is therefore used consistently across animals, plants, and some fungi. In most plants, the male function is part of a flower that produces pollen.

Sex determination

In many animal species, sex is determined by chromosomes. In mammals, the typical system is XY: an individual with one X and one Y chromosome usually develops as male, since the Y chromosome carries genes that initiate male development. Birds use a different system, ZW, in which the male has two Z chromosomes. In some reptiles, such as crocodilians, the temperature at which an egg incubates determines sex. In certain insects, such as bees, males develop from unfertilized eggs.

Reproductive organs and hormones

In mammals, the primary male reproductive organs are the testes, which serve two functions: producing sperm and secreting hormones such as testosterone. These hormones influence the development of reproductive structures during fetal life and drive changes in adolescence, such as increased muscle mass and voice changes. Sperm production proceeds continuously throughout much of adult life, unlike the limited egg production in females.

Environmental variation

In some species, males and females have different appearances (sexual dimorphism): they may differ in size, color, or specific features such as horns. In other species they are similar. Some organisms are hermaphrodites, such as earthworms and many plants, combining both male and female functions in a single individual. Certain fish can change sex during their lifetime, switching from female to male or vice versa.