Although there is a tendency to think of the embryo as a relatively sexless creature, his or her sex is determined at the moment of fertilization. The sperm contributes either an X or a Y chromosome to pair with the X chromosome of the female ovum. Barring any idiosyncracies during cell division, the outcome is either an XX (female) or XY (male) combination.

The XX or XY chromosomal combination in turn determines whether the undifferentiated fetal gonads become ovaries or testes at about 5 to 6 weeks of fetal life. After this point in sexual differentiation, the sex chromosomes appear to have no more direct influence.

Because homosexuality is the most common of variations in object choice, it has been the most intensely studied. Homosexuality has been viewed as an illness, a criminal offense, and a normal life style in Western society.

There has been controversy in the literature as to the serum testosterone levels of homosexual men. Kolodny and associates reported significantly lower plasma testosterone levels for homosexual men than for a control group of heterosexual subjects, suggesting that homosexuality may be related to hormonal levels. A recent report by Birk and associates4 disputes the above finding.

Kissing is common in our society, but it is performed in several manners, ranging from casual to "deep kissing." In other cultures kissing may be considered dirty, since it requires touching of mouths and perhaps the contact with another's saliva.

Manipulation of the female genitalia by the male is a common part of foreplay in several societies in addition to our own. Oral stimulation of the female genitalia (cunnilingus) was practiced by nearly half of the well-educated Kinsey males and has been found among other cultures. Many variations of this approach are described by Ford and Beach.

Similar patterns that distinguished men from women were found within each racial group: in general, women were less permissive than men. Reiss theorized that the lower the traditional level of sexual permissiveness the more likely it is that social factors will be able to alter individual levels of sexual permissiveness. It is interesting to note that white women's permissiveness was influenced by all the variables in the study, whereas none of the variables seemed to influence permissiveness among black men. Reiss suggests that differences between races may be analogous to differences between sexes, and that if one desires to study change in degree of sexual permissiveness, the group that is less permissive should be studied, since it is most likely to change.

The "pretense of orgasm," long perpetuated as the manner in which women respond to sexual stimulation, has perhaps limited interaction between sex partners, which in turn has limited their capacity for sexual satisfaction. Changes that affected a woman's social or life cycle demands often resulted in reorienting of her sexual focus, especially in relation to preferred actions of the partner and coital techniques. Although no change in physiologic indices of orgasmic response was seen to accompany social change, reported subjective pleasure in orgasm reflected desirable or undesirable social change. Masters and Johnson concluded that achievement of orgasm is dependent on the psychosocial acceptance of sexuality more than on aggressive behavior in the female.

Nonmarital intercourse has been a cause for concern in many cultures. Proscriptive codes that condemned nonmarital intercourse were developed even in ancient civilizations (more to ensure that property rights were safeguarded than to protect morals). Despite modern social codes, most men have intercourse prior to marriage. Class differences account for variation in men's ages at first coitus. Among men in the Kinsey sample who had attended college, 67% had had coitus before marriage; for those who finished high school, the percentage was 84%; and for those who did not progress beyond grade school, 98% had had premarital coitus. Sexual outlet for college-age men was a prostitute or companion in 21% of the cases, but for men of lower educational levels, 68% had experienced coitus with a prostitute or companion. Only a very small proportion of contacts were between upper-class men and prostitutes. By age 21, about 75% of the male population had had coitus. In male sexual practices there was a major departure from the publicly held and overtly expressed attitudes toward premarital coitus.