15-6 What has research taught us about sexual orientation?

We express the direction of our sexual interest in our sexual orientation—our enduring sexual attraction toward members of our own sex (homosexual orientation), the other sex (heterosexual orientation), or both sexes (bisexual orientation). Cultures vary in their attitudes toward same-sex attractions. “Should society accept homosexuality?” Yes, say 88 percent of Spaniards, 80 percent of Canadians, and 1 percent of Nigerians, with women everywhere being more accepting than men (Pew, 2013). Yet whether a culture condemns or accepts same-sex unions, heterosexuality prevails and homosexuality exists. In African countries, in most of which same-sex relationships are illegal, the prevalence of people who are lesbian, gay, or bisexual “is no different from other countries in the rest of the world,” reports the Academy of Science of South Africa (2015).

How many people are exclusively homosexual? About 10 percent, as the popular press has often assumed? Or 20 percent, as the average American estimated in a 2013 survey (Jones et al., 2014)? According to more than a dozen national surveys in Europe and the United States, a better estimate is about 3 or 4 percent of men and 2 percent of women (Chandra et al., 2011; Herbenick et al., 2010; Savin-Williams et al., 2012). When Gallup asked 121,290 Americans about their sexual identity—“Do you, personally, identify as lesbian, gay, bisexual, or transgender?”—3.4 percent answered Yes (Gates & Newport, 2012). When the National Center for Health Statistics asked 34,557 Americans about their sexual identity, they found essentially the same result: All but 3.4 percent answered “straight,” with 1.6 percent answering “gay” or “lesbian” and 0.7 percent saying “bisexual” (Ward et al., 2014).

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Survey methods that absolutely guarantee people’s anonymity reveal another percent or two of nonheterosexual people (Coffman et al., 2013). Moreover, people in less tolerant places are more likely to hide their sexual orientation. About 3 percent of California men express a same-sex preference on Facebook, for example, as do only about 1 percent in Mississippi. Yet about 5 percent of Google pornography searches in both states are for gay porn. And Craigslist ads for males seeking “casual encounters” with other men tend to be at least as common in less tolerant states, where there are also more Google searches for “gay sex” and “Is my husband gay?” (MacInnis & Hodson, 2015; Stephens-Davidowitz, 2013).

Fewer than 1 percent of people—for example, only 12 people out of 7076 Dutch adults in one survey (Sandfort et al., 2001)—reported being actively bisexual. A larger number of adults—13 percent of women and 5 percent of men in a U.S. National Center for Health Statistics survey—report some same-sex sexual contact during their lives (Chandra et al., 2011). And still more have had an occasional homosexual fantasy. In laboratory assessments, some self-identified bisexual men show a homosexual arousal pattern by responding with genital arousal mostly to male erotic images. Others exhibit increased viewing time and genital arousal to both male and female images (Cerny & Janssen, 2011; Lippa, 2013; Rieger et al., 2013; Rosenthal et al., 2012).

What does it feel like to have same-sex attractions in a heterosexual culture? If you are heterosexual, one way to understand is to imagine how you would feel if you were socially isolated for openly admitting or displaying your feelings toward someone of the other sex. How would you react if you overheard people making crude jokes about heterosexual people, or if most movies, TV shows, and advertisements portrayed (or implied) homosexuality? And how would you answer if your family members were pleading with you to change your heterosexual “lifestyle” and to enter into a homosexual marriage?

Facing such reactions, some individuals struggle with their sexual attractions, especially during adolescence and if feeling rejected by parents or harassed by peers. If lacking social support, nonheterosexual teens may experience lower self-esteem and higher anxiety and depression (Becker et al., 2014; Kwon, 2013), as well as an increased risk of contemplating suicide (Plöderl et al., 2013; Ryan et al., 2009; Wang et al., 2012). They may at first 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 change (Haldeman, 1994, 2002; Myers & Scanzoni, 2005).

Today’s psychologists therefore view sexual orientation as neither willfully chosen nor willfully changed. “Efforts to change sexual orientation are unlikely to be successful and involve some risk of harm,” declared a 2009 American Psychological Association report. 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.

This conclusion is most strongly established for men. Women’s sexual orientation tends to be less strongly felt and potentially more fluid and changing (Chivers, 2005; Diamond, 2008; Dickson et al., 2013). In general, men are sexually simpler. Their lesser sexual variability is apparent in many ways (Baumeister, 2000). Compared with men, women’s sexual drive and interests are more flexible and varying. Women, for example, more often prefer to alternate periods of high sexual activity with periods of almost none (Mosher et al., 2005). In their pupil dilation and genital responses to erotic videos, and in their implicit attitudes, heterosexual women exhibit more bisexual attraction than do men (Rieger & Savin-Williams, 2012; Snowden & Gray, 2013). Baumeister calls women’s more varying sexuality a difference in erotic plasticity.

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So, our sexual orientation is something we do not choose and (especially for males) cannot change. Where, then, do these preferences come from? See if you can anticipate the conclusions that have emerged from hundreds of research studies by responding Yes or No to the following questions:

The answer to all these questions has been No (Storms, 1983). In a search for possible environmental influences on sexual orientation, Kinsey Institute investigators interviewed nearly 1000 homosexuals and 500 heterosexuals. They assessed nearly every imaginable psychological cause of homosexuality—parental relationships, childhood sexual experiences, peer relationships, dating experiences (Bell et al., 1981; Hammersmith, 1982). Their findings: Homosexuals are no more likely than heterosexuals to have been smothered by maternal love or neglected by their father. In one national survey of nearly 35,000 adults, those with a same-sex attraction were somewhat more likely to report having experienced child sexual abuse. But 86 percent of the men and 75 percent of the women with same-sex attraction reported no such abuse (Roberts et al., 2013).

And consider this: If “distant fathers” were more likely to produce homosexual sons, then shouldn’t boys growing up in father-absent homes more often be gay? (They are not.) And shouldn’t the rising number of such homes have led to a noticeable increase in the gay population? (It has not.) Most children raised by gay or lesbian parents grow up straight (Gartrell & Bos, 2010).

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. The lack of evidence for environmental causes of homosexuality has motivated researchers to explore possible biological influences. They have considered these possibilities:

SAME-SEX ATTRACTION IN OTHER SPECIES In Boston’s Public Gardens, caretakers solved the mystery of why a much-loved swan couple’s eggs never hatched. Both swans were female. In New York City’s Central Park Zoo, penguins Silo and Roy spent several years as devoted same-sex partners. Same-sex sexual behaviors have also been observed in several hundred other species, including grizzlies, gorillas, monkeys, flamingos, and owls (Bagemihl, 1999). Among rams, for example, some 7 to 10 percent display same-sex attraction by shunning ewes and seeking to mount other males (Perkins & Fitzgerald, 1997). Homosexual behavior seems a natural part of the animal world.

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GAY-STRAIGHT BRAIN DIFFERENCES Researcher Simon LeVay (1991) studied sections of the hypothalamus (a brain structure linked to emotion) taken from deceased heterosexual and homosexual people. As a gay scientist, LeVay wanted to do “something connected with my gay identity.” To avoid biasing the results, he did a blind study, not knowing which donors were gay. For nine months he peered through his microscope at a cell cluster he thought might be important. Then, one morning, he broke the code: One cell cluster was reliably larger in heterosexual men than in women and homosexual men. “I was almost in a state of shock,” LeVay said (1994). “I took a walk by myself on the cliffs over the ocean. I sat for half an hour just thinking what this might mean.”

It should not surprise us that brains differ with sexual orientation. Remember, everything psychological is simultaneously biological. But when did the brain difference begin? At conception? During childhood or adolescence? Did experience produce the difference? Or was it genes or prenatal hormones (or genes via prenatal hormones)?

LeVay does not view this cell cluster as an “on-off button” for sexual orientation. Rather, he believes it is an important part of a brain pathway that is active during sexual behavior. He agrees that sexual behavior patterns could influence the brain’s anatomy. (Neural pathways in our brain do grow stronger with use.) In fish, birds, rats, and humans, brain structures vary with experience—including sexual experience (Breedlove, 1997). But LeVay believes it more likely that brain anatomy influences sexual orientation. His hunch seems confirmed by the discovery of a similar difference found between the male sheep that do and don’t display same-sex attraction (Larkin et al., 2002; Roselli et al., 2002, 2004). Moreover, such differences seem to develop soon after birth, perhaps even before birth (Rahman & Wilson, 2003).

Since LeVay’s discovery, other researchers have reported additional gay-straight brain activity differences. One is an area of the hypothalamus that governs sexual arousal (Savic et al., 2005). When straight women were given a whiff of a scent derived from men’s sweat (which contains traces of male hormones), this area became active. Gay men’s brains responded similarly to the men’s scent. Straight men’s brains did not. They showed the arousal response only to a female hormone sample. In a similar study, lesbians’ responses differed from those of straight women (Kranz & Ishai, 2006; Martins et al., 2005).

GENETIC INFLUENCES Evidence indicates a genetic influence on sexual orientation. “Homosexuality does appear to run in families,” noted Brian Mustanski and Michael Bailey (2003). Researchers have speculated about possible reasons why “gay genes” might exist in the human gene pool, given that same-sex couples cannot naturally reproduce. One possible answer is kin selection. Evolutionary psychologists remind us that many of our genes also reside in our biological relatives. Perhaps, then, gay people’s genes live on through their supporting the survival and reproductive success of their nieces, nephews, and other relatives. Gay men make generous uncles, suggests one study of Samoans (Vasey & VanderLaan, 2010).

A fertile females theory suggests that maternal genetics may also be at work (Bocklandt et al., 2006). Homosexual men tend to have more homosexual relatives on their mother’s side than on their father’s (Camperio-Ciani et al., 2004, 2009, 2012; VanderLaan et al., 2011, 2012). And the relatives on the mother’s side also produce more offspring than do the maternal relatives of heterosexual men. Perhaps the genes that dispose some women to conceive more children with men also dispose some men to be attracted to men (LeVay, 2011). Thus, the decreased reproduction by gay men appears offset by the increased reproduction by their maternal extended family.

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Studies of twins also indicate that genes influence sexual orientation. Identical twins (who have identical genes) are somewhat more likely than fraternal twins (whose genes are not identical) to share a homosexual orientation (Alanko et al., 2010; Lángström et al., 2010). However, because sexual orientation differs in many identical twin pairs (especially female twins), other factors must also play a role.

In genetic studies of fruit flies, researchers have altered a single gene and changed the flies’ sexual orientation and behavior (Dickson, 2005). During courtship, females acted like males (pursuing other females) and males acted like females (Demir & Dickson, 2005). With humans, it’s likely that multiple genes, possibly in interaction with other influences, shape sexual orientation. A genome-wide study of 409 pairs of gay brothers identified sexual orientation links with areas of two chromosomes, one maternally transmitted (Sanders et al., 2015).

PRENATAL INFLUENCES Twins share not only genes, but also a prenatal environment. Two sets of findings indicate that the prenatal environment matters.

First, in humans, a critical period for fetal brain development seems to be the second trimester (Ellis & Ames, 1987; Garcia-Falgueras & Swaab, 2010; Meyer-Bahlburg, 1995). Exposure to the hormone levels typically experienced by female fetuses during this period may predispose a person (female or male) to be attracted to males in later life. When pregnant sheep were injected with testosterone during a similar critical period, their female offspring later showed homosexual behavior (Money, 1987).

Second, the mother’s immune system may play a role in the development of sexual orientation. Men who have older brothers are somewhat more likely to be gay—about one-third more likely for each additional older brother (Blanchard, 2004, 2008a,b, 2014; Bogaert, 2003). If the odds of homosexuality are roughly 2 percent among first sons, they would rise to nearly 3 percent among second sons, 4 percent for third sons, and so on for each additional older brother (see FIGURE 15.2). The reason for this curious effect—called the older-brother or fraternal birth-order effect—is unclear. But the explanation does seem biological. The effect does not occur among adopted brothers (Bogaert, 2006a). Researchers suspect the mother’s immune system may have a defensive response to substances produced by male fetuses. After each pregnancy with a male fetus, the maternal antibodies may become stronger and may prevent the fetal brain from developing in a typical male pattern.

On several traits, gays and lesbians appear to fall midway between straight females and males (TABLE 5.1 below; see also LeVay, 2011; Rahman & Koerting, 2008). Gay men tend to be shorter and lighter than straight men—a difference that appears even at birth. Women in same-sex marriages were mostly heavier than average at birth (Bogaert, 2010; Frisch & Zdravkovic, 2010).

Gay-straight spatial abilities also differ. On mental rotation tasks such as the one illustrated in FIGURE 15.3 below, straight men tend to outscore straight women but the scores of gays and lesbians fall between those of straight men and women (Rahman et al., 2004, 2008). But straight women and gays have both outperformed straight men at remembering objects’ spatial locations in tasks like those found in memory games (Hassan & Rahman, 2007).

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Taken together, the brain, genetic, and prenatal findings offer strong support for a biological explanation of sexual orientation (LeVay, 2011; Rahman & Koerting, 2008). Although “much remains to be discovered,” concludes Simon LeVay (2011, p. xvii), “the same processes that are involved in the biological development of our bodies and brains as male or female are also involved in the development of sexual orientation.”

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