Strong Bodybuilding Man Portrait

A great deal is now known about the development of masculine characteristics. The process of sexual differentiation specific to the reproductive system of Homo sapiens produces a female by default. The SRY gene on the Y chromosome, however, interferes with the default process, causing a chain of events that, all things being equal, leads to testes formation, androgen production and a range of both natal and post-natal hormonal effects covered by the terms masculinization or virilization. Because masculinization redirects biological processes from the default female route, it is more precisely called defeminization.
There is an extensive debate about how children develop gender identities.
In many cultures displaying characteristics not typical to one's gender may become a social problem for the individual. Among men, some non-standard behaviors may be considered a sign of homosexuality, while a girl who exhibits masculine behavior is more frequently dismissed as a "tomboy". Within sociology such labeling and conditioning is known as gender assumptions and is a part of socialization to better match a culture's mores. The corresponding social condemnation of excessive masculinity may be expressed in terms such as "machismo" or "testosterone poisoning."
The relative importance of the roles of socialization and genetics in the development of masculinity continues to be debated. While social conditioning obviously plays a role, it can also be observed that certain aspects of the masculine identity exist in almost all human cultures.