Portrait of Man. A man is an adult male human. Like most other male mammals, a man's genome typically inherits an X chromosome from his mother and a Y chromosome from his father. The male fetus produces larger amounts of androgens and smaller amounts of estrogens than a female fetus. This difference in the relative amounts of these sex steroids is largely responsible for the physiological differences that distinguish men from women. During puberty, hormones which stimulate androgen production result in the development of secondary sexual characteristics, thus exhibiting greater differences between the sexes. However, there are exceptions to the above for some transgender and intersex men. The English term man is derived from a Proto-Indo-European root *man-. More directly, the word derives from Old English mann. The Old English form had a default meaning of adult male, 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. In human beings, the sex of an individual is 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. On the other hand, if a sperm cell carrying a Y chromosome fertilizes the egg, the offspring will typically be male. Persons whose anatomy or chromosomal makeup differ from this pattern are referred to as intersex. Like most other male mammals, a man's genome typically inherits an X chromosome from his mother and a Y chromosome from his father. The male fetus produces larger amounts of androgens and smaller amounts of estrogens than a female fetus. This difference in the relative amounts of these sex steroids is largely responsible for the physiological differences that distinguish men from women. 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. Primary sex characteristics are characteristics that are present at birth and are integral to the reproductive process. For men, primary sex characteristics include the penis and testicles. Secondary sex characteristics are features that appear during puberty in humans. Such features are especially evident in the sexually dimorphic phenotypic traits that distinguish between the sexes, but--unlike the primary sex characteristics--are not directly part of the reproductive system. Secondary sexual characteristics that are specific to men include: Facial hair;. Chest hair;. Broadened shoulders;. An enlarged larynx; and. A voice that is significantly deeper than the voice of a child or a woman. The male reproductive system includes external and internal genitalia. The male external genitalia consist of the penis, the male urethra, and the scrotum, while the male internal genitalia consist of the testes, the prostate, the epididymis, the seminal vesicle, the vas deferens, the ejaculatory duct, and the bulbourethral 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 study of male reproduction and associated organs is called andrology. In mammals, the hormones that influence sexual differentiation and development are androgens, 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-Mullerian hormone, which inhibits the development of the Mullerian ducts. For males during puberty, testosterone, along with gonadotropins released by the pituitary gland, stimulates spermatogenesis. In general, men suffer from many of the same illnesses as women.