Understanding Psychology (10th Ed)

extramarital sex
Sexual activity 
between a married person and 
someone who is not his or her spouse.
homosexuals
Persons who are 
sexually attracted to members of 
their own sex.
bisexuals
Persons who are sexually 
attracted to people of the same sex 
and the other sex.
FIGURE 3
Once a couple is past their 
mid-30s, the average number of times 
per month they have sexual intercourse 
declines. Why do older couples have 
intercourse less frequently than younger 
ones? 
(Clements, 1994)
9 
0 
A
verage incidence of sexual inter
course per month 
18–24 25–34 
Age 
35–44 45–54 55–65 
1 
2 
5 
3 
6 
4 
7 
8 
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368 Chapter 
11 
Sexuality and Gender
sexual orientation is dependent on a person’s sexual feelings and behaviors and 
romantic feelings (Weinberg, Williams, & Pryor, 1991). 
What determines whether people become homosexual or heterosexual? Although 
there are a number of theories, none has proved completely satisfactory. 
Some explanations for sexual orientation are biological, suggesting that there are 
genetic causes. Evidence for a genetic origin of sexual orientation comes from studies 
of identical twins. The studies found that when one twin identifi ed himself or herself 
as homosexual, the occurrence of homosexuality in the other twin was higher than it 
was in the general population. Such results occur even for twins who have been sepa-
rated early in life and who therefore are not necessarily raised in similar social environ-
ments (Hamer et al., 1993; Turner, 1995; Kirk, Bailey, & Martin, 2000; Gooren, 2006). 
Hormones also may play a role in determining sexual orientation. For example, 
research shows that women exposed before birth to DES (diethylstilbestrol—a drug 
their mothers took to avoid miscarriage) were more likely to be homosexual or bisex-
ual (Meyer-Bahlburg, 1997). 
Some evidence suggests that differences in brain structures may be related to 
sexual orientation. For instance, the structure of the anterior hypothalamus, an area of 
the brain that governs sexual behavior, differs in male homosexuals and heterosexuals. 
Similarly, other research shows that, compared with heterosexual men or women, gay 
men have a larger anterior commissure, which is a bundle of neurons connecting the 
right and left hemispheres of the brain (LeVay, 1993; Byne, 1996; Witelson et al., 2008). 
However, research suggesting that biological causes are at the root of homosexu-
ality is not conclusive because most fi ndings are based on only small samples of 
individuals. Still, the possibility is real that some inherited or biological factor exists 
that predisposes people toward homosexuality if certain environmental conditions are 
met (Veniegas, 2000; Teodorov et al., 2002; Rahman, Kumari, & Wilson, 2003). 
Little evidence suggests that sexual orientation is brought about by child-rearing 
practices or family dynamics. Although proponents of psychoanalytic theories once 
argued that the nature of the parent-child relationship can produce homosexuality 
(e.g., Freud, 1922/1959), research evidence does not support such explanations (Isay, 
1994; Roughton, 2002). 
Another explanation for sexual orientation rests on learning theory (Masters & 
Johnson, 1979). According to this view, sexual orientation is learned through rewards 
and punishments in much the same way that we may learn to prefer swimming over 
tennis. For example, a young adolescent who had an unpleasant heterosexual expe-
rience might develop disagreeable associations with the other sex. If the same person 
had a rewarding, pleasant gay or lesbian experience, homosexuality might be incor-
porated into his or her sexual fantasies. If such fantasies are used during later sexual 
activities—such as masturbation—they may be positively reinforced through orgasm, 
and the association of homosexual behavior and sexual pleasure eventually may 
cause homosexuality to become the preferred form of sexual behavior.