Sexuality continues to develop throughout the lifespan. It may be expressed in singlehood, cohabitation, marriage, extramarital relationships, relationships following divorce, or in a variety of contexts as the individual ages.

Young adults grow toward sexual maturity. Many do so in the context of a single relationship that results in marriage. Others are involved in two or more relationships before they begin to live with or marry someone. Never-married people over 25 may find themselves part of the "singles scene." Blacks are more likely to remain single than whites.

Cohabitation is a stage that up to 40 percent of people experience. The time couples spend living together varies from a few months to several years. Sixty percent of cohabiting couples marry. Some cohabiting couples have children, either together or with previous partners. Men and women who are living together engage in sexual activity more often, on average, than those who are married or dating.

Marriage represents a major turning point as couples face new responsibilities and problems, and try to find time for each other. Married couples in their twenties engage in sexual intercourse two or three times per week on average, with the frequency declining to two or three times per month among couples over 60. Perhaps the most dramatic change in marital sex practices in recent decades is the increased popularity of oral-genital sex. Many people continue to masturbate even though they are married. Most people today-both women and men-express general satisfaction with their marital sex life. Sexual patterns in marriage, however, show great variability.

About 25 percent of all married men and 15 percent of all married women engage in extramarital sex at some time. Extramarital sex is disapproved of in our society and is generally carried on in secrecy. In a few cases, it is agreed that both husband and wife can have extramarital sex, as in open marriage, swinging, and polyamory. Equity theory and the sociobiological perspective may be helpful in understanding patterns of extramarital sex.

Virtually all widowed and divorced men return to an active sex life, as do most divorced women and about half of widowed women. A particular set of sexual norms characterizes the divorce subculture.

Research indicates that gay men have modified their sexual practices somewhat in the AIDS era. They have reduced their number of partners and have shifted away from risky sex practices. Among heterosexuals there is some evidence of a reduction in the number of partners, and slight improvements in condom use. Blacks and single persons are more likely to have changed. Most heterosexuals do not consider themselves at risk for HIV infection, however, so they are less concerned with safer sex practices.

While sexual activity declines somewhat with age, it is perfectly possible to remain sexually active into one's eighties or nineties. Problems with sex or the cessation of intercourse may be related to physical factors. In women, declining estrogen levels result in a thinner, less elastic vagina and less lubrication; in men, there is lowered testosterone production and increased vascular disease, combined with slower erections and longer refractory periods. Psychological factors can also be involved, such as the belief that the elderly cannot or should not have sex. Masters and Johnson emphasized that two factors are critical to maintaining sexual capacity in old age: good physical and mental health, and regularity of sexual expression. The AARP survey indicates that all sexual behaviors-including heterosexual intercourse and masturbation-may continue past age 70.