Human sexuality
Sexuality is the way people experience, and express themselves through, sexual activities. This involves biological, psychological, physical, erotic, emotional, social, or spiritual feelings and behaviors. Because it is a broad term which has varied within different historical contexts, it lacks a precise definition. The biological and physical aspects of sexuality largely concern the human reproductive functions, including the human sexual response cycle.
Someone's sexual orientation is their pattern of sexual interest in the opposite and/or same sex. Physical and emotional aspects of sexuality include bonds between individuals that are expressed through profound feelings or physical manifestations of love, trust, and care. Social aspects deal with the effects of human society on one's sexuality, while spirituality concerns an individual's spiritual connection with others. Sexuality also affects and is affected by cultural, political, legal, philosophical, moral, ethical, and religious aspects of life.
Interest in sexual activity normally increases when an individual reaches puberty. Although no single theory on the cause of sexual orientation has yet gained widespread support, there is considerably more evidence supporting nonsocial causes than social ones, especially for males. Hypothesized social causes are supported by only weak evidence, distorted by numerous confounding factors. This is further supported by cross-cultural evidence because the incidence of homosexuality is not significantly higher in cultures that are more tolerant of it.
Evolutionary perspectives on human coupling, reproduction and reproduction strategies, and social learning theory provide further views of sexuality. Sociocultural aspects of sexuality include historical developments and religious beliefs. Some cultures have been described as sexually repressive. The study of sexuality also includes human identity within social groups, sexually transmitted infections, and birth control methods.
Development
Sexual orientation
There is considerably more evidence supporting innate causes of sexual orientation than learned ones, especially for males. This evidence includes the cross-cultural correlation of homosexuality and childhood gender nonconformity, moderate genetic influences found in twin studies, evidence for prenatal hormonal effects on brain organization, the fraternal birth order effect, and the finding that in rare cases where infant males were raised as girls due to physical differences or deformity, they nevertheless turned out attracted to females. Hypothesized social causes are supported by only weak evidence, distorted by numerous confounding factors.Cross-cultural evidence also leans more toward non-social causes. Cultures that are very tolerant of homosexuality do not have significantly higher rates of it. Homosexual behavior is relatively common among boys in British single-sex boarding schools, but adult Britons who attended such schools are no more likely to engage in homosexual behavior than those who did not. In an extreme case, the Sambia people ritually require their boys to engage in homosexual behavior during adolescence before they have any access to females, yet most of these boys go on to lead heterosexual lives.
It is not fully understood why genes causing homosexuality persist in the gene pool. One hypothesis involves kin selection, suggesting that homosexuals invest heavily enough in their relatives to offset the cost of not reproducing as much directly. This has not been supported by studies in Western cultures, but several studies in Samoa have found some support for this hypothesis. Another hypothesis involves sexually antagonistic genes, which cause homosexuality when expressed in males but increase reproduction when expressed in females. Studies in both Western and non-Western cultures have found support for this hypothesis.
Gender differences
Psychological theories exist regarding the development and expression of gender differences in human sexuality. A number of them agree in predicting that men should be more approving of casual sex and should also be more promiscuous than women. These theories are mostly consistent with observed differences in males' and females' attitudes toward casual sex before marriage in the United States. Other aspects of human sexuality, such as sexual satisfaction, incidence of oral sex, and attitudes toward homosexuality and masturbation, show little to no observed difference between males and females. Observed gender differences regarding the number of sexual partners are modest, with males tending to have slightly more than females.Biological and physiological aspects
Like other mammals, humans are primarily grouped into either the male or female sex.The biological aspects of human sexuality deal with the reproductive system, the sexual response cycle, and the factors that affect these aspects. They also deal with the influence of biological factors on other aspects of sexuality, such as organic and neurological responses, heredity, hormonal issues, gender issues, and sexual dysfunction.
Physical anatomy and reproduction
Males and females are anatomically similar; this extends to some degree to the development of the reproductive system. As adults, they have different reproductive mechanisms that enable them to perform sexual acts and to reproduce. Men and women react similarly to sexual stimuli with minor differences. Women have a monthly reproductive cycle, whereas the male sperm production cycle is more continuous.Brain
The hypothalamus is the most important part of the brain for sexual functioning. This is a small area at the base of the brain consisting of several groups of nerve cell bodies that receive input from the limbic system. Studies have shown that within lab animals, the destruction of certain areas of the hypothalamus causes the elimination of sexual behavior. The hypothalamus is important because of its relationship to the pituitary gland, which lies beneath it. The pituitary gland secretes hormones that are produced in the hypothalamus and itself. The four important sexual hormones are oxytocin, prolactin, follicle-stimulating hormone, and luteinizing hormone.Oxytocin, sometimes referred to as the "love hormone", is released in both sexes during sexual intercourse when an orgasm is achieved. Oxytocin has been suggested as critical to the thoughts and behaviors required to maintain close relationships. The hormone is also released in women when they give birth or are breastfeeding. Prolactin and oxytocin are responsible for inducing milk production in women. Follicle-stimulating hormone is responsible for ovulation in women, and acts by triggering egg maturity; in men, it stimulates sperm production. Luteinizing hormone triggers ovulation, which is the release of a mature egg.
Male anatomy and reproductive system
Males have both internal and external genitalia that are responsible for procreation and sexual intercourse. Production of spermatozoa is also cyclic, but unlike the female ovulation cycle, the sperm production cycle is constantly producing millions of sperm daily.External male anatomy
The external male genitalia are the penis and the scrotum.The penis provides a passageway for sperm and urine. The penis consists of nerves, blood vessels, fibrous tissue, and three parallel cylinders of spongy tissue. Other components of the penis include the shaft, glans, root, cavernous bodies, and spongy body. The three cylindrical bodies of spongy tissue, which are filled with blood vessels, run along the length of the shaft. The two bodies that lie side by side in the upper portion of the penis are the corpora cavernosa. The third, called the corpus spongiosum, is a tube that lies centrally beneath the others and expands at the end to form the tip of the penis. During arousal, these bodies erect the penis by filling with blood.
The raised rim at the border of the shaft and glans is called the corona. The urethra connects the urinary bladder to the penis where urine exits the penis through the urethral meatus. The urethra eliminates urine and acts as a channel for semen and sperm to exit the body during sexual intercourse. The root consists of the expanded ends of the cavernous bodies, which fan out to form the crura and attach to the pubic bone and the expanded end of the spongy body. The bulb of the penis is surrounded by the bulbospongiosus muscle, while the corpora cavernosa are surrounded by the ischiocavernosus muscles. These aid urination and ejaculation. The penis has a foreskin that typically covers the glans; this is sometimes removed by circumcision for medical, religious or cultural reasons. In the scrotum, the testicles are held away from the body, one possible reason for this is so sperm can be produced in an environment slightly lower than normal body temperature.
The penis has very little muscular tissue, and this exists in its root. The shaft and glans have no muscle fibers. Unlike most other primates, male humans lack a penile bone.
Internal male anatomy
Male internal reproductive structures are the testicles, the duct system, the prostate and seminal vesicles, and the Cowper's gland.The testicles, are where sperm and male hormones are produced. Millions of sperm are produced daily in several hundred seminiferous tubules. Cells called the Leydig cells lie between the tubules; these produce hormones called androgens; these consist of testosterone and inhibin. The testicles are held by the spermatic cord, which is a tubelike structure containing blood vessels, nerves, the vas deferens, and a muscle that helps to raise and lower the testicles in response to temperature changes and sexual arousal, in which the testicles are drawn closer to the body.
Sperm gets transported through a four-part duct system. The first part of this system is the epididymis. The testicles converge to form the seminiferous tubules, coiled tubes at the top and back of each testicle. The second part of the duct system is the vas deferens, a muscular tube that begins at the lower end of the epididymis. The vas deferens passes upward along the side of the testicles to become part of the spermatic cord. The expanded end is the ampulla, which stores sperm before ejaculation. The third part of the duct system is the ejaculatory ducts, which are -long paired tubes that pass through the prostate gland, where semen is produced. The prostate gland is a solid, chestnut-shaped organ that surrounds the first part of the urethra, which carries urine and semen. Similar to the female G-spot, the prostate provides sexual stimulation and can lead to orgasm through anal sex.
The prostate gland and the seminal vesicles produce seminal fluid that is mixed with sperm to create semen. The prostate gland lies under the bladder and in front of the rectum. It consists of two main zones: the inner zone that produces secretions to keep the lining of the male urethra moist and the outer zone that produces seminal fluids to facilitate the passage of semen. The seminal vesicles secrete fructose for sperm activation and mobilization, prostaglandins to cause uterine contractions that aid movement through the uterus, and bases that help neutralize the acidity of the vagina. The Cowper's glands, or bulbourethral glands, are two pea-sized structures beneath the prostate.