Separate sexes evolved many times over, and nobody knows when males first appeared
Males and females did not arise once in some ancient ancestor. The split into two kinds of sex cell evolved independently in different lineages, a textbook case of convergent evolution. Sexual reproduction is at least 1.2 billion years old, but the fossil record says nothing about when the first male emerged.
Biologically, a male is an organism that produces sperm, or is organised to, the small sex cell that fuses with the larger egg. Across species, sex is defined by that gamete type alone, and differences between males and females in one lineage do not reliably predict those in another. In most mammals, including humans, males carry a Y chromosome, which drives higher testosterone production and the development of male reproductive organs.
The evolutionary path seems to repeat. Early sexual species had mating types that looked and behaved identically, labelled simply plus or minus. Some lineages then evolved gametes of two sizes, and some went further to the extreme in which the egg is huge and immobile. One strong argument is that the mechanics of getting two cells together pushed evolution that way. Many theories share a thread: bigger female gametes survive better, while smaller male ones move faster and find partners more easily. Why a few species remain with equal gametes is still unexplained. In the green algae called Volvocales, females evolved from the plus type, and one theory holds that males descend from the dominant minus type. Some males can even reproduce alone, through androgenesis.
Maleness is not only an animal trait. Chytrids, diatoms and land plants make male gametes, and in plants the terms extend to the spore-producing structures that give rise to male and female individuals.
The word came into English via Old French masle from Latin masculus, a diminutive of mas, meaning a male person or animal. The familiar circle-and-arrow symbol is the astronomical sign for Mars, first applied to sex by Carl Linnaeus in 1751. It is popularly read as the war god's shield and spear, but William T. Stearn called that fanciful, siding with the 17th-century scholar Claude de Saumaise, who traced it to an abbreviation of a Greek name for the planet.
Source: Male
