Sexual Orientation, Controversy, and Science 637616Research-Article2016
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PSIXXX10.1177/1529100616637616Bailey et al.Sexual Orientation, Controversy, and Science 637616research-article2016 Psychological Science in the Public Interest Sexual Orientation, Controversy, 2016, Vol. 17(2) 45 –101 © The Author(s) 2016 Reprints and permissions: and Science sagepub.com/journalsPermissions.nav DOI: 10.1177/1529100616637616 pspi.sagepub.com J. Michael Bailey1, Paul L. Vasey2, Lisa M. Diamond3, S. Marc Breedlove4, Eric Vilain5,6,7,8, and Marc Epprecht9,10 1Department of Psychology, Northwestern University; 2Department of Psychology, University of Lethbridge; 3Department of Psychology, University of Utah; 4Neuroscience Program, Michigan State University; 5Department of Human Genetics, University of California, Los Angeles; 6Department of Pediatrics, University of California, Los Angeles; 7Department of Urology, University of California, Los Angeles; 8Joint International Unit on Epigenetics, Data, and Politics, Centre National de la Recherche Scientifique, Paris, France; 9Department of History, Queen’s University; and 10Department of Global Development Studies, Queen’s University Summary Ongoing political controversies around the world exemplify a long-standing and widespread preoccupation with the acceptability of homosexuality. Nonheterosexual people have seen dramatic surges both in their rights and in positive public opinion in many Western countries. In contrast, in much of Africa, the Middle East, the Caribbean, Oceania, and parts of Asia, homosexual behavior remains illegal and severely punishable, with some countries retaining the death penalty for it. Political controversies about sexual orientation have often overlapped with scientific controversies. That is, participants on both sides of the sociopolitical debates have tended to believe that scientific findings—and scientific truths—about sexual orientation matter a great deal in making political decisions. The most contentious scientific issues have concerned the causes of sexual orientation—that is, why are some people heterosexual, others bisexual, and others homosexual? The actual relevance of these issues to social, political, and ethical decisions is often poorly justified, however. Keywords sexual orientation, causes, sex differences, social implications Introduction Our review has led us to the following conclusions. Sexual orientation refers to relative sexual attraction This article has two related goals. The first is to provide a to men, to women, or to both. People who are sexually current summary of scientific findings regarding sexual attracted to the same sex (whom we denote as “nonhet- orientation. Although we focus most on causation, we erosexual”) represent a minority of adults. Those with also address other scientific issues concerning sexual ori- predominantly same-sex attractions comprise fewer than entation, including its meaning and measurement, sex 5% of respondents in most Western surveys. Data from differences in its expression, its development, and its non-Western cultures are consistent with this conclusion. expression across time and place. Regarding causation, There is no persuasive evidence that the rate of same-sex we provide a taxonomy of causal hypotheses and review attraction has varied much across time or place. evidence for them. These include hormonal, genetic, Male and female sexual orientations differ in several social environmental, and nonsocial environmental influ- respects. Women are more likely to report a bisexual ences. Our second goal is less scientific and more analyti- than an exclusively same-sex orientation; men show the cal: to criticize and improve common but incorrect opposite pattern. Men’s sexual orientations are closely reasoning in this domain. For example, the commonly phrased question of whether sexual orientation is “a Corresponding Author: choice” is a poor one for advancing either scientific J. Michael Bailey, Northwestern University, Swift Hall 303B, 2029 understanding or policy. A more meaningful formulation Sheridan Rd., Evanston, IL 60208-2710 is whether sexual orientation is socially influenced. E-mail: [email protected] 46 Bailey et al. linked to their pattern of sexual arousal to male versus because it is politically controversial. This is a mis- female erotic stimuli; women’s are not. Women appear take. In fact, the more politically controversial a more likely than men to experience same-sex attraction topic, the more it is in the public interest to illumi- in the context of close affectionate relationships, and nate it in a revealing and unbiased manner. Our their patterns of sexual attraction appear more likely to article is offered in the spirit of progress toward exhibit change over time. that end. Across many different cultures, male and female non- 2. Scientists, activists, and policy makers should rea- heterosexuality in adulthood tends to be preceded by son more carefully regarding potential ethical or childhood gender nonconformity: a pattern of behavior policy implications of scientific findings. For somewhat like that of the other sex. Childhood gender example, the issue of whether sexual orientation nonconformity is a matter of degree, and it can range is chosen represents intellectual confusion, and from subtle to extreme. Often, it emerges at an early age, no scientific finding will illuminate this issue in despite conventional gender socialization. Among some any interesting way. Although clumsy reasoning adults, childhood gender nonconformity appears to per- may advantage a particular political position in sist into adulthood. the short term, in the long term, clear thinking is Individuals’ political attitudes about sexual orientation best for everyone. tend to correlate with their views of the causes of sexual 3. The most common meaningful controversy across orientation. Those who hold positive attitudes (i.e., that time and place has concerned the extent to which there is nothing inherently wrong with nonheterosexual- homosexuality is socially influenced and, more ity or its open expression) have tended to believe that specifically, whether or not it spreads as a result of sexual orientation is due to nonsocial causes such as contagion and social tolerance. There is no good genetics. Those who hold negative attitudes (i.e., that evidence that either increases the rate of homo- nonheterosexuality is undesirable or immoral and that sexual orientation, although tolerance may facili- society should restrict its free expression) have tended to tate behavioral expression of homosexual desire. believe that homosexuality has social causes, such as Suppressing homosexual behavior imposes an early sexual experiences and cultural acceptance of non- immense burden on homosexually oriented peo- heterosexuality. We refer to these as the “nonsocial” and ple and serves no apparent legitimate social goal “social” hypotheses, respectively. Both hypotheses that cannot be reached in other ways. require direct scientific support; neither can claim confir- mation solely because support for the other is weak. The political rights of lesbian, gay, and bisexual (LGB) No causal theory of sexual orientation has yet gained men and women have dramatically improved in many widespread support. The most scientifically plausible Western countries during the past 50 years. In the United causal hypotheses are difficult to test. However, there is States, for example, the Supreme Court ruled in June considerably more evidence supporting nonsocial causes 2015 that individual states must allow marriages between of sexual orientation than social causes. This evidence same-sex couples. This result would have been unthink- includes the cross-culturally robust finding that adult able in 1965, when homosexual behavior was illegal, homosexuality is strongly related to childhood gender homosexual inclinations were a source of shame, and nonconformity; moderate genetic influences demon- most Americans believed homosexuality was a mental strated in well-sampled twin studies; the cross-culturally illness (e.g., “The Homosexual in America,” 1966). As of robust fraternal-birth-order effect on male sexual orienta- May 2015, 118 nations do not criminalize homosexual tion; and the finding that when infant boys are surgically behavior (Carroll & Itaborahy, 2015). and socially “changed” into girls, their eventual sexual The trajectory of LGB rights has been quite different in orientation is unchanged (i.e., they remain sexually many other parts of the world, however. Currently, 75 attracted to females). In contrast, evidence for the most countries legally proscribe homosexual behavior. Eleven commonly hypothesized social causes of homosexual- countries—all in Africa, Asia and the Middle East—retain ity—sexual recruitment by homosexual adults, patterns the death penalty as a possible sanction for homosexual of disordered parenting, or the influence of homosexual acts1 (International Lesbian and Gay Association, 2015; parents—is generally weak in magnitude and distorted Stewart, 2015). by numerous confounding factors. It might be tempting to assume that much of the world With respect to scientific and social policy, we offer is lagging behind but will ultimately follow the more three general conclusions: accepting Western nations toward tolerance. That out- come is not assured, however. In some nations, tolerance 1. Scientifically, sexual orientation is an important, of homosexuality appears to be decreasing. For example, fundamental trait that has been understudied Uganda has been struggling with the