NCBI Bookshelf. Sex differences of importance to health and human disease occur throughout the life span, although the specific expression of these differences varies at different stages of life. Some differences originate in events occurring in the intrauterine environment, where developmental processes differentially organize tissues for later activation in the male or female. In the prenatal period, sex determination and differentiation occur in a series of sequential processes governed by genetic and environmental factors. During the pubertal period, behavioral and hormonal changes manifest the secondary sexual characteristics that reinforce the sexual identity of the individual through adolescence and into adulthood. Hormonal events occurring in puberty lay a framework for biological differences that persist through life and that contribute to variable onset and progression of disease in males and females.
Human sexuality is the way people experience and express themselves sexually. Someone's sexual orientation is their pattern of sexual interest in the opposite or same sex. 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.
Human sexual activity , any activity—solitary, between two persons, or in a group—that induces sexual arousal. The objective here is to describe and explain both sets of factors and their interaction. It should be noted that taboos in Western culture and the immaturity of the social sciences for a long time impeded research concerning human sexual activity, so that by the early 20th century scientific knowledge was largely restricted to individual case histories that had been studied by such European writers as Sigmund Freud , Havelock Ellis , and Richard, Freiherr baron von Krafft-Ebing. By the s, however, the foundations had been laid for the more extensive statistical studies that were conducted before World War II in the United States. Much of the following discussion rests on the findings of the Institute for Sex Research, which constitute the most comprehensive data available.
The images below illustrate the male and female body parts that are involved in sexual activity and reproduction. These body parts are also commonly referred to as genitals, reproductive organs, or sex organs. The male body has sexual organs both inside and outside the body. The internal organs include the epididymis, vas deferens, seminal vesicles, and prostate, and the external organs include the penis and testicles.