Male

There is a good argument that this pattern was driven by the physical constraints on the mechanisms by which two gametes get together as required for sexual reproduction.[11][page needed].

[19][17]: 222  Although sexual evolution emerged at least 1.2 billion years ago, the lack of anisogamous fossil records make it hard to pinpoint when males evolved.

According to William T. Stearn, however, this derivation is "fanciful" and all the historical evidence favours "the conclusion of the French classical scholar Claude de Saumaise (Salmasius, 1588–1683)" that it is derived from θρ, the contraction of a Greek name for the planet Mars, which is Thouros.

[28] Species that are divided into females and males are classified as gonochoric in animals, as dioecious in seed plants[2] and as dioicous in cryptogams.

[36] In some species of reptiles, such as 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.

[37] In tropical clown fish, the dominant individual in a group becomes female while the other ones are male.

[38] Male animals have evolved to use secondary sex characteristics as a way of displaying traits that signify their fitness.

Differences in physical size and the ability to fulfill the requirements of sexual selection have contributed significantly to the outcome of secondary sex characteristics in each species.

This is often attributed to the need for male mammals to be physically stronger and more competitive in order to win mating opportunities.

[42][page needed] This is true for many species of birds where the male displays more vibrant colors than the female, making them more noticeable to potential mates.

These characteristics have evolved over time as a result of sexual selection, as males who exhibited these traits were more successful in attracting mates and passing on their genes.