Strong Bodybuilding Man Portrait

In mankind, the sex of an individual is generally determined at the time of fertilization by the genetic material carried in the sperm cell. If a sperm cell carrying an X chromosome fertilizes the egg, the offspring will typically be female (XX); if a sperm cell carrying a Y chromosome fertilizes the egg, the offspring will typically be male (XY). Persons whose anatomy or chromosomal makeup differ from this pattern are referred to as intersex.
This is referred to as the XY sex-determination system and is typical of most mammals, but quite a few other sex-determination systems exist, including some that are non-genetic.
The term primary sexual characteristics denotes the kind of gamete the gonad produces: the ovary produces egg cells in the female, and the testis produces sperm cells in the male. The term secondary sexual characteristics denotes all other sexual distinctions that play indirect roles in uniting sperm and eggs. Secondary sexual characteristics include everything from the specialized male and female features of the genital tract, to the brilliant plumage of male birds or facial hair of humans, to behavioral features such as courtship.
Biological factors are not sufficient determinants of whether a person considers themselves a man or is considered a man. Intersex individuals, who have physical and/or genetic features considered to be mixed or atypical for one sex or the other, may use other criteria in making a clear determination. There are also transgender or transsexual men, who were born or physically assigned as female at birth, but identify as men; there are varying social, legal and individual definitions with regard to these issues.