By far the greatest amount of sociosexual activity is heterosexual activity between only one male and one female. Heterosexual activity frequently begins in childhood, and, while much of it may be motivated by curiosity, such as showing or examining genitalia, many children engage in sex play because it is pleasurable. The sexual impulse and responsiveness are present in varying degrees in most children and latent in the remainder. With adolescence, sex play is superseded by dating, which is socially encouraged, and dating almost inevitably involves some physical contact resulting in sexual arousal. This contact is a part of the learning process and may also ultimately be a part of courtship and the selection of a marriage partner.

Hugging, kissing, and generalized caresses of the clothed body and techniques involving genital stimulation, known as foreplay, may be done for its own sake as an expression of affection and a source of pleasure, and it may occur as a preliminary to coitus. In a minority of cases, but a substantial minority, these forms of contact can lead to orgasm and may be a substitute for coitus. Excluding foreplay, physical contact is usually very stereotyped, beginning with hugging and kissing and gradually escalating to stimulation of the breasts and genitalia. It may be initiated by the male or by the female; the individual who receives contact generally rejects or accepts the other person’s overtures but refrains from playing a more aggressive role. Such physical contact, in some form, is a near-universal human experience and is valuable not only in mate selection but as a means of learning how to interact with another person sexually.

Coitus, the insertion of the penis into the vagina, is viewed by society quite differently depending upon the marital status of the individuals. The majority of human societies permit premarital coitus, at least under certain circumstances. In more repressive societies, it is more likely to be tolerated (but not encouraged) if the individuals intend marriage. Marital coitus often is perceived as an obligation in most societies. Extramarital coitus is generally condemned in a small majority of societies. In addition, about two-thirds of societies are more lenient toward males than females regarding extramarital coitus. This double standard of morality is also seen in premarital life. Postmarital coitus (i.e., coitus by separated, divorced, or widowed persons) is almost always ignored. Even societies that try to confine coitus to marriage recognize the difficulty of trying to force abstinence upon sexually experienced and usually older persons.

In the United States and much of Europe, there has been a progressive trend toward an increase in premarital coitus, such that today, a majority of males and females have experienced premarital coitus. The proportions for this experience vary in different groups and socioeconomic classes.

Extramarital coitus continues to be openly condemned but is becoming more tolerated secretly, particularly if mitigating circumstances are involved. In some areas, such as southern Europe and Latin America, extramarital coitus is expected of most husbands and is accepted by society if the activity is not too flagrant. The wives do not generally approve but are resigned to what they believe to be a masculine propensity. In the United States, about the mid- and latter part of the 20th century, small organizations or clubs existed to provide extramarital coitus for married couples. Despite the publicity they have engendered, however, extremely few individuals belonged to such organizations. Most extramarital coitus is done secretly without the knowledge of the spouse. Most husbands and wives feel very possessive of their spouses and interpret extramarital activity as an aspersion on their own sexual adequacy, as indicating a loss of affection and as being a source of social disgrace.

Humans are not inherently monogamous but have a natural desire for diversity in their sexuality as in other aspects of life. Some societies have provided a release for these desires by suspending the restraints on extramarital coitus on special occasions or with certain individuals, and in some modern societies a certain amount of extramarital flirtation is not considered unusual behavior.

Discussion of sociosexual activity would be incomplete without some note of the role it has played in ceremony and religion. While the major religions of today are to varying degrees antisexual, many religions have incorporated sexual activity into their rites and ceremonies. Humans’ ancient and continuing interest in their own fertility and in that of food plants and animals makes such a connection between sex and religion inevitable, particularly among peoples with uncertain food supplies. In most religions the deities were considered to have active sexual lives and sometimes took a sexual interest in humans. In this regard it is noteworthy that in Christianity sexual activity is absent in heaven and sexual proclivities are ascribed only to evil supernatural beings: Satan, devils, incubi, and succubi (spirits or demons who seek out sleeping humans for sexual intercourse).

Whether or not a behavior is interpreted by society or the individual as erotic (i.e., capable of engendering sexual response) depends chiefly on the context in which the activity occurs. A kiss, for example, may express asexual affection (as a kiss between relatives), respect (a French officer kissing a soldier after bestowing a medal), or reverence (kissing the hand or foot of a pope), or it may be a casual salutation and social amenity. Even something as specific as touching genitalia is not construed as sexual if done for medical reasons. In other words, the apparent motivation of the activity determines its interpretation.

Individuals are extremely sensitive in judging motivations: a greeting kiss, if protracted more than a second or two, takes on a sexual connotation, and studies have shown that if an adult male at a party stands closer than the length of his hand and forearm to a female, she generally imputes a sexual motive to his proximity. Nudity may be construed as erotic or even as a sexual invitation—unless it occurs in a medical context, in a group consisting of but one gender, or in a nudist camp.

Sexual response

Sexual response follows a pattern of sequential stages or phases when sexual activity is continued. First, there is the excitement phase marked by increase in pulse and blood pressure, an increase in blood supply to the surface of the body resulting in increased skin temperature, flushing, and swelling of all distensible body parts (particularly noticeable in the penis and female breasts), more rapid breathing, the secretion of genital fluids, vaginal expansion, and a general increase in muscle tension. These symptoms of arousal eventually increase to a near maximal physiological level, the plateau phase, which is generally of brief duration. If stimulation is continued, orgasm usually occurs. Orgasm is marked by a feeling of sudden intense pleasure, an abrupt increase in pulse rate and blood pressure, and spasms of the pelvic muscles causing vaginal contractions in the female and ejaculation by the male. Involuntary vocalization may also occur. Orgasm lasts for a few seconds (normally not over 10), after which the individual enters the resolution phase, the return to a normal or subnormal physiological state. Up to the resolution phase, males and females are the same in their response sequence, but, whereas males return to normal even if stimulation continues, continued stimulation can produce additional orgasms in females. In brief, after one orgasm a male becomes unresponsive to sexual stimulation and cannot begin to build up another excitement phase until some period of time has elapsed, but females are physically capable of repeated orgasms without the intervening “rest period” required by males.