One’s anatomy and sexuality change with age. The changes are rapid in intra-uterine life and around puberty but are much slower and gradual in other phases of the life cycle.

The reproductive organs first develop in the same form for both males and females: internally there are two undifferentiated gonads and two pairs of parallel ducts (Wolffian and Müllerian ducts); externally there is a genital protrusion with a groove (urethral groove) below it, the groove being flanked by two folds (urethral folds). On either side of the genital protrusion and groove are two ridgelike swellings (labioscrotal swellings). Around the fourth week of life the gonads differentiate into either testes or ovaries. If testes develop, the hormone they secrete causes the Müllerian duct to degenerate and almost vanish and causes the Wolffian duct to elaborate into the sperm-carrying tubes and related organs (the vas deferens, epididymis, and seminal vesicles, for example). If ovaries develop, the Wolffian duct deteriorates, and the Müllerian duct elaborates to form the fallopian tubes, uterus, and part of the vagina. The external genitalia simultaneously change. The genital protrusion becomes either a penis or clitoris. In the female the groove below the clitoris stays open to form the vulva, and the folds on either side of the groove become the inner lips of the vulva (the labia minora). In the male these folds grow together, converting the groove into the urethral tube of the penis. The ridgelike swellings on either side remain apart in the female and constitute the large labia (labia majora), but in the male they grow together to form the scrotal sac into which the testes subsequently descend.

At birth both male and female have all the neurophysiological equipment necessary for sexual response, although the reproductive system is not at this stage functional. Sexual interests, sexual activity, and sexual response are seen with increasing frequency in most children from infancy on. Even newborn males have penile erections, and babies of both sexes seem to find pleasure in genital stimulation. What appears to be orgasm has been observed in infant boys and girls, and, later in childhood, orgasm definitely can occur in masturbation or sex play.

Puberty may be defined as that short period of time (generally two years) during which the reproductive system matures and the secondary sexual characteristics appear. The ovaries and testes begin producing much larger amounts of hormones, pubic hair appears, female breasts develop, the menstrual cycle begins in females, spermatozoa and viable eggs are produced, and males experience voice change and a sudden acceleration in growth. Puberty generally occurs in females about age 12–13 and in males about 13–14, but there is much individual variation. With puberty there is generally an intensification or the first appearance of sexual interest. Puberty marks the beginning of adolescence.

Adolescence, from a physical viewpoint, is that period between puberty and the attainment of one’s maximum height. By the latter point, which occurs about age 16 in females and 18 in males, the individual has adult anatomy and physiology. In late adolescence the majority of individuals are probably at their peak in terms of sexual capacity: the ability to respond quickly and repeatedly. During this period the sex drive is at its maximum in males, although it is difficult to say whether this is also true of females, since female sexuality, in many societies, is frequently suppressed during adolescence.

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Following adolescence there are about three decades of adult life during which physiological changes are slow and gradual. While muscular strength increases for a time, the changes may best be described as slow deterioration. This physical decline is not immediately evident in sexual activity, which often increases in quantity and quality as the individual develops more social skills and higher socioeconomic status and loses some of the inhibitions and uncertainties that often impede adolescent sexuality. Indeed, in the case of the United States female, the deterioration is more than offset by her gradual loss of sexual inhibition, and the effect of age is not clear until menopausal symptoms begin. In the male, however, there is no such masking of deterioration, and the frequency of sexual activity and the intensity of interest and response slowly, but inexorably, decline.

After age 50 most females have experienced menopausal symptoms, and most males have been forced to recognize their increasing physical limitations. With menopause, the female genitalia gradually begin to atrophy and the amount of vaginal secretion diminishes—this is the direct consequence of the cessation of ovarian function and can be prevented, or the symptoms reversed, by administering estrogen. If a female has had a good sexual adjustment prior to menopause and if she does not believe in the fallacy that it spells the end of sexual life, menopause will have no adverse effect on her sexual and orgasmic ability. There is reason to believe that if a woman remains in good health and genital atrophy is prevented, she could enjoy sexual activity regardless of age. Males in good health are also capable of continuing sexual activity, although with an ever-decreasing frequency, throughout old age. The male has more difficulty in achieving erection, cannot maintain erection as long, and must have longer and longer “rest periods” between sexual acts. The amount of ejaculate becomes less, but most old males are still fertile. The Cowper’s gland secretion (called “precoital mucus”) diminishes or disappears entirely. According to Kinsey’s data, about one-quarter of males are impotent by age 65, one-half by age 75, and three-quarters by age 80. One must remember, however, that some unknown but certainly substantial proportion of this impotence may be attributed to poor health.

In general, the female withstands the onslaughts of age better than the male. The reduction in the frequency of marital intercourse or even its abandonment is more often than not the result of male deterioration.

Effects of early conditioning

Physiology sets only very broad limits on human sexuality; most of the enormous variation found among humans must be attributed to the psychological factors of learning and conditioning.

The human infant is born simply with the ability to respond sexually to tactile stimulation. It is only later and gradually that the individual learns or is conditioned to respond to other stimuli, to develop a sexual attraction to males or females or both, to interpret some stimuli as sexual and others as nonsexual, and to control in some measure his or her sexual response. In other words, the general and diffuse sexuality of the infant becomes increasingly elaborated, differentiated, and specific.

The early years of life are, therefore, of paramount importance in the development of what ultimately becomes adult sexual orientation. There appears to be a reasonably fixed sequence of development. Before age five, children develop a sense of gender identity, think of themselves as boys or girls, and begin to relate to others differently according to their gender. Through experience children learn what behavior is rewarded and what is punished and what sorts of behavior are expected of them. Parents, peers, and society in general teach and condition children about sex not so much by direct informational statements and admonitions as by indirect and often unconscious communication. Children soon learn, for example, that they can touch any part of their body or someone else’s body except the anal–genital region. Children rubbing their genitals find that this quickly attracts adult attention and admonishment or that adults will divert them from this activity. It becomes clear that there is something peculiar and taboo about this area of the body. This “genital taboo” is reinforced by the great concern over children’s excretory behavior: bladder and bowel control is praised; loss of control is met by disappointment, chiding, and expressions of disgust. Obviously, the anal–genital area is not only a taboo area but a very important one as well. It is almost inevitable that the genitalia become associated with anxiety and shame. It is noteworthy that this attitude finds expression in the language of Western civilizations, as in “privates” (something to be kept hidden) and the German word for the genitals, Scham (“shame”).

While all children in Western civilizations experience this antisexual teaching and conditioning, a few have, in addition, atypical sexual experiences, such as witnessing or hearing sexual intercourse or having sexual contact with an older person. The effects of such atypical experiences depend upon how children interpret them and upon the reaction of adults if the experience comes to their attention. Seeing parental coitus is harmless if children interpret it as playful wrestling but harmful if they consider it as hostile, assaultive behavior. Similarly, an experience with an adult may seem merely a curious and pointless game, or it may be a hideous trauma leaving lifelong psychic scars. In many cases the reaction of parents and society determines the child’s interpretation of the event. What would have been a trivial and soon-forgotten act becomes traumatic if the mother cries, the father rages, and the police interrogate the child.

Some atypical developments occur through association during the formative years. A child may associate clothing, especially underclothing, stockings, and shoes with gender and sex and thereby establish the basis for later fetishism or transvestism. Others, having been spanked or otherwise punished for self-masturbation or childhood sex play, form an association between punishment, pain, and sex that could escalate later into sadism or masochism. It is not known why some children form such associations whereas others with apparently similar experience do not.

About the age that children enter puberty, parents and society, who more often than not refuse to recognize that children have sexual responses and capabilities, finally face the inescapable reality and consequently begin inculcating children with their attitudes and standards regarding sex. This campaign by adults is almost wholly negative: the child is told what not to do. While dating may be encouraged, no form of sexual activity is advocated or held up as model behavior. The message usually is: “Be popular [i.e., sexually attractive] but abstain from sexual activity.” This antisexualism is particularly intense regarding young females and is reinforced by reference to pregnancy, sexually transmitted diseases, and, most important, social disgrace. To this list religious families add the concept of the sinfulness of premarital sexual expression. With young males the double standard of morality still prevails. The youth receives a double message: “Don’t do it, but we expect that you will.” No such loophole in the prohibitions is offered young girls. Meanwhile, the young male’s peer group is exerting a prosexual influence, and his social status is enhanced by his sexual exploits or by exaggerated reports thereof.

As a result of this double standard of sexual morality, the relationship between young males and females often becomes a ritualized contest, the male attempting to escalate the sexual activity and the female resisting his efforts. Instead of mutuality and respect, one often has a struggle in which the female is viewed as a reluctant sexual object to be exploited, and the male is viewed as a seducer and aggressor who must succeed in order to maintain his self-image and his status with his peers. This sort of pathological relationship causes a lasting attitude on the part of females: men are not to be trusted; they are interested only in sex; a girl dare not smile or be friendly lest males interpret it as a sign of sexual availability, and so forth. Such an aura of suspicion, hostility, and anxiety is scarcely conducive to the development of warm, trusting relationships between males and females. Fortunately, love or infatuation usually overcomes this negativism with regard to particular males, but the average female still maintains a defensive and skeptical attitude toward men.

Western society is replete with attitudes that impede the development of a healthy attitude toward sex. The free abandon so necessary to a full sexual relationship is, in the eyes of many, an unseemly loss of self-control, and self-control is something one is urged to maintain from infancy onward. Panting, sweating, and involuntary vocalization are incompatible with the image of dignity. Worse yet is any substance once it has left the body: it immediately becomes unclean. The male and female genital fluids are generally regarded with disgust—they are not only excretions but sexual excretions. Here again, societal concern over excretion is involved, for sexual organs are also urinary passages and are in close proximity to the “dirtiest” of all places—the anus. Lastly, many individuals in society regard menstrual fluid with disgust and abstain from sexual intercourse during the four to six days of flow. This attitude is formalized in Judaism, in which menstruating females are specifically labelled as ritually unclean.

In view of all these factors working against a healthy, rational attitude toward sex and in view of the inevitable disappointments, exploitations, and rejections that are involved in human relationships, one might wonder how anyone could reach adulthood without being seriously maladjusted. The sexual impulse, however, is sufficiently strong and persistent and repeated sexual activity gradually erodes the inhibitions and any sense of guilt or shame. Further, all humans have a deep need to be esteemed, wanted, and loved. Sexual activity with another is seen as proof that one is attractive, desired, valued, and possibly loved—a proof very necessary to self-esteem and happiness. Hence, even among the very inhibited or those with weak sex drive, there is this powerful motivation to engage in sociosexual activity.

Most persons ultimately achieve at least a tolerable sexual adjustment. Some unfortunates, nevertheless, remain permanently handicapped, and very few completely escape the effects of society’s antisexual conditioning. While certain inhibitions and restraints are socially and psychologically useful—such as deferring gratification until circumstances are appropriate and modifying activity out of regard for the feelings of others—most people labor under an additional burden of useless and deleterious attitudes and restrictions.