The English term "man" is derived from a Proto-Indo-European root *man- (see Sanskrit/Avestan manu-, Slavic m?ž "man, male"). More directly, the word derives from Old English mann. The Old English form had a default meaning of "adult male" (which was the exclusive meaning of wer), though it could also signify a person of unspecified gender. The closely related Old English pronoun man was used just as it is in Modern German to designate "one" (e. g., in the saying man muss mit den Wölfen heulen). The Old English form is derived from Proto-Germanic *mannz, "human being, person", which is also the etymon of German Mann "man, husband" and man "one" (pronoun), Old Norse maðr, and Gothic manna. According to Tacitus, the mythological progenitor of the Germanic tribes was called Mannus. *Manus in Indo-European mythology was the first man, see Mannus, Manu (Hinduism).

The term manhood is used to describe the period in a human male's life after he has transitioned from boyhood, having passed through puberty, usually having attained male secondary sexual characteristics, and symbolises a male's coming of age. The word man is used to mean any adult male. In English-speaking countries, many other words can also be used to mean an adult male such as guy, dude, buddy, bloke, fellow, chap and sometimes boy or lad. The term manhood is associated with masculinity and virility, which refer to male qualities and male gender roles.

Humans exhibit sexual dimorphism in many characteristics, many of which have no direct link to reproductive ability, although most of these characteristics do have a role in sexual attraction. Most expressions of sexual dimorphism in humans are found in height, weight, and body structure, though there are always examples that do not follow the overall pattern. For example, men tend to be taller than women, but there are many people of both sexes who are in the mid-height range for the species.

Some examples of male secondary sexual characteristics in humans, those acquired as boys become men or even later in life, are:

• more pubic hair
• more facial hair
• larger hands and feet
• broader shoulders and chest
• larger skull and bone structure
• larger brain mass and volume
• greater muscle mass
• a more prominent Adam's apple and deeper voice
• greater height
• a higher tibia:femur ratio (a longer shinbone in comparison to the thighbone)

Sexual characteristics

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.

Gender

Biological factors are not sufficient determinants of whether a person considers themselves a man or is considered a man. Intersex individuals, who have physical 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 and transsexual men, who were assigned as female at birth, but identify as men; there are varying social, legal and individual definitions with regard to these issues. (See trans man.)

Reproductive system

The male sex organs are part of the reproductive system, consisting of the penis, testicles, vas deferens, and the prostate gland. The male reproductive system's function is to produce semen which carries sperm and thus genetic information that can unite with an egg within a woman. Since sperm that enters a woman's uterus and then fallopian tubes goes on to fertilize an egg which develops into a fetus or child, the male reproductive system plays no necessary role during the gestation. The concept of fatherhood and family exists in human societies. The study of male reproduction and associated organs is called andrology.

Sex hormones

In mammals, the hormones that influence sexual differentiation and development are androgens (mainly testosterone), which stimulate later development of the ovary. In the sexually undifferentiated embryo, testosterone stimulates the development of the Wolffian ducts, the penis, and closure of the labioscrotal folds into the scrotum. Another significant hormone in sexual differentiation is the Anti-müllerian hormone, which inhibits development of the Müllerian ducts.

Illnesses

In general, men suffer from many of the same illnesses as women. In comparison to women, men suffer from slightly more illnesses. Male life expectancy is slightly lower than female life expectancy, although the difference has narrowed in recent years.

For males during puberty, testosterone, along with gonadotropins released by the pituitary gland, stimulates spermatogenesis, along with the full sexual distinction of a human male from a human female, while women are acted upon by estrogens and progesterone to produce their sexual differences from the human male.

Masculinity has its roots in genetics (see gender). Therefore, while masculinity looks different in different cultures, there are common aspects to its definition across cultures. Sometimes gender scholars will use the phrase "hegemonic masculinity" to distinguish the most dominant form of masculinity from other variants. In the mid-twentieth century United States, for example, John Wayne might embody one form of masculinity, while Albert Einstein might be seen as masculine, but not in the same "hegemonic" fashion.

Anthropology has shown that masculinity itself has social status, just like wealth, race and social class. In western culture, for example, greater masculinity usually brings greater social status. Many English words such as virtue and virile (from the Indo-European root vir meaning man) reflect this.^[8] An association with physical or moral strength is implied. Masculinity is associated more commonly with adult men than with boys.

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 pre-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, the exhibition of feminine behavior may be considered a sign of homosexuality, while the same is for a woman who exhibits masculine behavior. 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.

The historical development of gender role is addressed by such fields as behavioral genetics, evolutionary psychology, human ecology and sociobiology. All human cultures seem to encourage the development of gender roles, through literatur