Man: Encyclopedia II - Man - Biology and sex

Man - Biology and sex

In terms of sex, men have various sexual characteristics that differentiate them from women. Just as in women, the sex organs of a man are part of the reproductive system, consisting of the penis, testicles, vas deferens and other sperm cords, and the prostate gland. The male reproductive system is oriented around producing and ejaculating semen which carries sperm and thus genetic information. 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 every human society.

The secondary sex characteristics, such as body hair and muscle growth, are involved in attracting a mate or in defeating rivals. But these secondary traits are also often related to reproduction in some manner. In contrast to women, men have sex organs that are mostly considered to be external, although many parts of the male reproductive system are internal as well (such as the prostate). The study of male reproduction and associated organs is called andrology. Most, but not all, men have the karyotype 46/XY.

In general, men suffer from many of the same illnesses as women. However, there are some sex-related illnesses that occur only, or more frequently, in men. For example, autism and color blindness are more common in men than women. As well, some age-related disorders such as Alzheimer's disease appear to be more common among men, though whether this is due to a genuinely higher incidence or because men have lower life expectancies than women is uncertain.

Biological factors are usually not the sole determinants of whether a person considers themselves a man or is considered a man or not. For example, several men have been born without a typical male physiology (estimates range between one in 2,000 and one in 100,000), or some individuals with XY chromosomes can have an hormonal or genetic difference (such as androgen insensitivity syndrome), or another intersex condition; some of those intersex people, and others, who have had a sex assigned at birth seek reassignment later in their lives. (See also gender identity, gender role and transman.)

Additionally, 20% of males, particularly in the U.S., the Philippines, and South Korea, as well as Jews and Muslims from all countries, have experienced circumcision, a process of altering the penis from its natural state by removing the foreskin.

Adapted from the Wikipedia article "Biology and sex", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki