The human sex drive is a powerful motivator for many activities in our
lives. Although it provides for reproduction and improvement of the
gene pool, it also has a nonbiological, sociocultural dimension. Sexuality
begins before birth, as sexual anatomy is determined by the sex determining
chromosome complement that we receive at fertilization.
Females receive two X chromosomes. Males receive one X and one Y sex determining
chromosome. It is the presence and activity of the SRY gene
that causes male development and its absence or inactivity that allows female
development.
At puberty, hormones influence the development of secondary
sex characteristics and the functioning of gonads. As the ovaries and
testes begin to produce gametes, fertilization becomes possible. Sexual
reproduction involves the production of gametes by meiosis in the
ovaries and testes. The production and release of these gametes is controlled by the interaction of hormones. In males, each cell that undergoes
spermatogenesis results in four sperm; in females, each cell that
undergoes oogenesis results in one oocyte and two polar bodies. Successful
sexual reproduction depends on proper hormone balance,
proper meiotic division, fertilization, placenta formation, proper diet
of the mother, and birth. Hormones regulate ovulation and menstruation
and may also be used to encourage or discourage ovulation. Fertility
drugs, the patch and birth-control pills, for example, involve
hormonal control. A number of contraceptive methods have been developed,
including the diaphragm, condom, IUD, spermicidal jellies
and foams, contraceptive implants, the sponge, tubal ligation, and
vasectomy.
Hormones continue to direct our sexuality throughout our lives.
Even after menopause, when fertilization and pregnancy are no longer
possible for a female, normal sexual activity can continue in both women
and men.
