Sexual Orientation and Science

Dr. Myers' textbooks in psychology are widely used in schools across North America. This excerpt is from David G. Myers'Exploring Psychology 4th edition (Worth Publishers, 1999). Excerpted and reformatted with the permission of Worth Publishers. A similar section appears in Dr. Myers'Psychology 5th edition (Worth Publishers, 1998).


We express the direction of our sexual interest in our sexual orientation--our enduring sexual attraction toward members of a particular gender.

As far as we know, all cultures in all times have been predominantly heterosexual (Bullough, 1990). Yet, cultures vary in their attitude toward homosexuality. Whether a culture condemns and punishes homosexuality or views it as an acceptable alternative, homosexuality survives and heterosexuality prevails.

Homosexual people often recall childhood play preferences like those of the other sex (Bailey & Zucker, 1995). But most homosexual people report not becoming aware of same-gender sexual feelings until during or shortly after puberty, and not thinking of themselves as gay or lesbian until around age 20 (Garnets & Kimmel, 1990).

How many people are exclusively homosexual?

Until recently, the popular press assumed a homosexuality rate of 10 percent. But in both Europe and the United States, more than a dozen national surveys in the early 1990s explored sexual orientation, using methods that protected the respondent's anonymity. Their results agree in suggesting that a more accurate figure is about 3 or 4 percent of men and 1 to 2 percent of women (Laumann & others, 1994; Smith, 1996).

Less than 1 percent of the respondents reported being actively bisexual, but a larger number of adults reported having had an isolated homosexual experience. And most people said they had had an occasional homosexual fantasy.

Although health experts find it helpful to know sexual statistics, numbers do not decide issues of human rights. Similarly, it's helpful in manufacturing school desks to know that about 10 percent of people are left-handed. But whether left-handers are 3 percent or 10 percent of the population doesn't answer the moral question of whether lefties should enjoy equal rights.

What does it feel like to be homosexual in a heterosexual culture?

One way for heterosexual people to understand is to imagine how they would feel...

  • if they were to be ostracized or fired for openly admitting or displaying their feelings toward someone of the other sex;
  • if they were to overhear people making crude jokes about heterosexual people;
  • if most movies, TV shows, and advertisements portrayed (or implied) homosexuality; and
  • if their family members were pleading with them to change their heterosexual life-style and to enter into a homosexual marriage.

Facing such reactions, homosexual people often struggle with their sexual orientation.

At first, they may try to ignore or deny their desires, hoping they will go away. But they don't.

Then they may try to change, through psychotherapy, willpower, or prayer. But the feelings typically persist, as do those of heterosexual people--who are similarly incapable of becoming homosexual (Haldeman, 1994).

Eventually, homosexuals may accept their orientation — by electing celibacy (as do some heterosexuals);

  • by engaging in promiscuous sex (a choice more commonly made by men than by women);
  • or by entering into a committed, long-term love relationship (a choice more often made by women than by men) (Peplau, 1982; Weinberg & Williams, 1974).

Most psychologists today view sexual orientation as neither willfully chosen nor willfully changed.

Sexual orientation in some ways is like handedness: Most people are one way, some the other. A very few are truly ambidextrous. Regardless, the way one is endures.

Nor is sexual orientation linked with psychological disorder or sexual crime. "Child molester" is not a sexual orientation. Some homosexuals do abuse children, but most child molesters are heterosexual males (Gonsiorek, 1982).

These facts led the American Psychiatric Association in 1973 to drop homosexuality from its list of "mental illnesses." Understanding Sexual Orientation

If our sexual orientation is indeed something we do not choose and cannot change, then where do these preferences come from? How do we move toward either a heterosexual or a homosexual orientation? Is homosexuality linked with problems in a child's relationships with parents, such as with a domineering mother and an ineffectual father or a possessive mother and a hostile father? As children, were many homosexuals molested, seduced, or otherwise sexually victimized by an adult homosexual? Are children who observe homosexual role models (such as parents) more likely to become homosexual?

Consider the findings of lengthy Kinsey Institute interviews with nearly 1000 homosexuals and 500 heterosexuals (Bell & others, 1981; Hammersmith, 1982). The investigators assessed nearly every imaginable psychological cause of homosexuality--parental relationships, childhood sexual experiences, peer relationships, dating experiences.

Their findings: Homosexuals were no more likely than heterosexuals to have been smothered by maternal love, neglected by their father, or sexually abused.

More recent studies have also found that sons of homosexual men were not more likely to become gay if they lived with their gay dad, and that 9 in 10 children of lesbian mothers developed into heterosexuals (Bailey & others, 1995; Golombok & Tasker, 1996).

If even being reared by a homosexual parent has no appreciable influence on sexual orientation, then having a gay or lesbian teacher or bus driver also seems unlikely to have an appreciable influence.

Homosexual people do, however, appear more often in certain populations:

In America's dozen largest cities, the percentage of men identifying themselves as gay jumps to 9 percent, compared with only 1 percent in rural areas (Binson & others, 1995; Laumann & others, 1994).

One study of the biographies of 1004 eminent people found homosexual and bisexual people overrepresented (11 percent of the sample), especially among poets (24 percent), fiction writers (21 percent), and artists and musicians (15 percent) (Ludwig, 1995).

For uncertain reasons, men who have older brothers are somewhat more likely to be gay, report Ray Blanchard and his colleagues (1995, 1996a,b, 1997). Assuming the odds of homosexuality are roughly 3 percent among first sons, they rise to 4 percent among second sons and 5 percent for third sons.

So, what determines sexual orientation?

One theory proposes that people develop same-sex erotic attachments if segregated by gender at the time their sex drive matures (Storms, 1981). But even in a tribal culture in which homosexual behavior is expected of all boys before marriage, heterosexuality prevails (Money, 1987). (As this illustrates, homosexual behavior does not always indicate a homosexual orientation.)

Another theory proposes the opposite: that people develop romantic attachments to those who differ from, and thus are more fascinating than, the peers they associated with while growing up (Bell, 1982).

The bottom line from a half-century's theory and research: If there are environmental factors that influence sexual orientation, we do not yet know what they are. If someone were to ask me, "What can I do to influence my child's sexual orientation?" my answer would have to be "I haven't a clue."

The Brain and Sexual Orientation

New research indicates that sexual orientation is at least partly physiological. Researcher Simon LeVay (1991) discovered this while studying sections of the hypothalamus taken from deceased heterosexual and homosexual people.

As a gay scientist, LeVay wanted to do "something connected with my gay identity," but he knew he had to avoid biasing the results. So he did the study "blind," without knowing which donors were gay. After nine months of peering through his microscope at a cell cluster he thought might be important, LeVay sat down one morning and broke the codes.

His discovery: The cell cluster was reliably larger in heterosexual men than in women and homosexual men. As the brain difference became apparent, "I was almost in a state of shock ... I took a walk by myself on the cliffs over the ocean. I sat for half an hour just thinking what this might mean" (LeVay, 1994).

It should not surprise us that brains differ with sexual orientation. Remember our maxim: Although we find it convenient to talk separately of psychological and biological explanations, everything psychological is simultaneously biological.

The critical questions are, can this finding be replicated? If so, when does the brain difference begin? At conception? In the womb? During childhood or adolescence? Does experience produce the difference? Or do genes or prenatal hormones (or genes via prenatal hormones)?

LeVay does not view this little neural center as a sexual orientation center; rather, he sees it as an important part of the neural pathway engaged in sexual behavior. Moreover, he acknowledges that it's possible that sexual behavior patterns influence the brain's anatomy. (In fish, rats, birds, and humans, brain structures are known to vary with experience.) But he believes it more likely that brain anatomy influences sexual orientation.

Laura Allen and Roger Gorski (1992) offered a similar conclusion after discovering that a section of the fibers connecting right and left hemispheres is one-third larger in homosexual men than in heterosexual men. "The emerging neuroanatomical picture," notes Brian Gladue (1994), "is that, in some brain areas, homosexual men are more likely to have female-typical neuroanatomy than are heterosexual men."

Genes and Sexual Orientation

The evidence suggests that genetic influence plays a role (Whitam & others, 1993).

One research team studied the twin brothers of homosexual men. Among their identical twin brothers, 52 percent were homosexual, as were 22 percent of fraternal twin brothers (Bailey & Pillard, 1991, 1995).

In a follow-up study of homosexual women, a similar 48 percent of their identical twins were homosexual, as were 16 percent of their fraternal twins (Bailey & others, 1993).

With half the identical twin pairs differing, we know that genes aren't the whole story. Moreover, a new study using a diverse sample of Australian twins found somewhat lower rates of sexual similarity--although, again, identical twins were more likely than fraternal twins to share homosexual feelings (Bailey & others, 1997).

This is the sort of pattern we expect to see when genes are having an influence. Moreover, with a single transplanted gene, scientists can now cause male fruit flies to display homosexual behavior (Zhang & Odenwald, 1995).

Prenatal Hormones and Sexual Orientation

The elevated rate of similar homosexual orientation even in fraternal twins might also result from their sharing the same prenatal environment. In animals, abnormal prenatal hormone conditions have altered the sexual orientation of a fetus.

German researcher Gunter Dorner (1976, 1988) pioneered this research by manipulating a fetal rat's exposure to male hormones, thereby "inverting" its sexual behavior toward rats of the other sex. Female sheep will likewise show homosexual behavior if their pregnant mothers are injected with testosterone during a critical gestation period (Money, 1987).

Atypical prenatal hormones may produce similar results in humans. A critical period for the human brain's neural-hormonal control system may exist between the middle of the second and fifth months after conception (Ellis & Ames, 1987; Gladue, 1990; Meyer-Bahlburg, 1995). It seems that exposure to the hormone levels typically experienced by female fetuses during this time may predispose the person (whether female or male) to be attracted to males in later life.

Some tests reveal that homosexual men have spatial abilities like those typical of heterosexual women--a pattern consistent with the hypothesis that homosexuals were exposed to atypical prenatal hormones (Gladue, 1994; McCormick & Witelson, 1991).

Curiously, gay men also have fingerprint patterns rather like those of heterosexual women. Most people have more fingerprint ridges on their right hand. Jeff Hall and Doreen Kimura (1994) observed that this right-versus-left difference is less true of females and gay males than of heterosexual males--a difference that these researchers believe is due to prenatal hormones.

Because the physiological evidence is preliminary and controversial, some scientists remain skeptical. Rather than specifying sexual orientation, perhaps biological factors predispose a temperament that influences sexuality "in the context of individual learning and experience" (Byne & Parsons, 1993).

Perhaps, theorizes Daryl Bem (1996), genes code for prenatal hormones and brain anatomy, which predispose temperaments that lead children to prefer sex-typical or sex-atypical activities and friends. These preferences may lead children later to feel attracted to whichever sex feels different. Boys with feminine interests may find masculine males exotic. This could explain why, in personal ads, gay men tend to seek masculine partners and lesbians feminine partners (Bailey & others, 1997).

The dissimilar-seeming sex (one's own, for homosexual people) becomes associated with anxiety and other forms of arousal, which eventually gets transformed into romantic arousal. The exotic becomes erotic.

Regardless of the process, the consistency of the genetic, prenatal, and brain findings has swung the pendulum toward a physiological explanation. Nature more than nurture, most psychiatrists now believe, predisposes sexual orientation (Vreeland & others, 1995). If biological influences prove critical (perhaps especially in certain environmental contexts), it would explain why sexual orientation is so difficult to change.

Still, some people wonder: Should the cause of sexual orientation matter?

Maybe it shouldn't, but people's assumptions matter. Those who believe (as most homosexual people believe) that sexual orientation is a biological given--an enduring identity, not a choice--express more accepting attitudes toward homosexual persons (Allen & others, 1996; Furnham & Taylor, 1990; Whitley, 1990).

In American surveys, agreement that homosexuality is "something that people are born with" doubled from 16 to 31 percent between 1983 and 1993. Over roughly the same period, support for equal job rights for homosexuals increased from 59 to 80 percent (Moore, 1993).

Between 1982 and 1996, agreement that "homosexuality should be an acceptable alternative lifestyle" also increased, from 34 to 44 percent (Gallup, 1996). Accepting attitudes are most common among women and those with a gay or lesbian friend or relative (Herek & Capitanio, 1996; Kite & Whitley, 1996).

To gay and lesbian activists, the new biological research is a double-edged sword (Diamond, 1993). If sexual orientation, like skin color and sex, is genetically influenced, that offers a further rationale for civil rights protection. Moreover, it may alleviate parents' concerns about their children having gay teachers and role models. It does, however, raise the haunting possibility that genetic markers of sexual orientation could someday be identified through fetal testing, and the fetus aborted.

Sex and Human Values

Recognizing that values are both personal and cultural, most sex researchers and educators strive to keep their writings on sexuality value-free. But can the study of sexual behavior and what motivates it really be free of values?

Those who think not say that the very words we use to describe behavior often reflect our personal values. When sex researchers label sexually restrained individuals as "erotophobic" and as having "high sex guilt," they express their own values.

Whether we label sexual acts we do not practice as "perversions," "deviations," or part of an "alternative sexual life-style" depends on our attitudes toward the behaviors. Labels both describe and evaluate.

When education about sex is separated from the context of human values, some students may get the idea that sexual intercourse is merely recreational activity. Diana Baumrind (1982), a University of California child-rearing expert, has observed that adolescents interpret sex education that pretends to be "value-free" as meaning that adults are neutral about adolescent sexual activity. Such an implication is unfortunate, she added, because "promiscuous recreational sex poses certain psychological, social, health, and moral problems that must be faced realistically."

Researchers have found that teenagers who have had formal sex education are no more likely to engage in premarital sex than those who have not (Furstenberg & others, 1985; Zelnik & Kim, 1982).

Moreover, we enrich our lives by knowing ourselves, by realizing that others share our feelings, by understanding what is likely to please or displease our loved one. Witness the crumbling of falsehoods about homosexuality. Witness the growing realization that some types of sexually explicit material can lead people to devalue or hurt others.

Perhaps we can agree that the knowledge provided by sex research is preferable to ignorance, yet also agree that researchers' values should be stated openly, enabling us to debate them and to reflect on our own values.

We might also remember that scientific research on sexual motivation does not aim to define the personal meaning of sex in our own lives. One can know every available fact about sex--that the initial spasms of male and female orgasm come at 0.8-second intervals, that the female nipples expand 10 millimeters at the peak of sexual arousal, that systolic blood pressure rises some 60 points and the respiration rate to 40 breaths per minute--but fail to understand the human significance of sexual intimacy.

Surely one significance of sexual intimacy is its expression of our deeply social nature. Sex is a socially significant act. Men and women can achieve orgasm alone, yet most people find greater satisfaction while embracing their loved one. There is a yearning for closeness in sexual motivation. Sex at its human best is life-uniting and love-renewing.