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Gay, Straight, and the Reason Why: The Science of Sexual Orientation

Simon LeVay
Published by Oxford University Press in 2010

Simon LeVay’s book is the latest and most effective among the growing corpus of books and articles arguing for an exclusively biological explanation of sexual orientation. The broad and methodologically uneven array of evidence pointing to biological contributions to the origin of sexual orientation, heterosexual and homosexual, continues to amass, sprawling across diverse disciplinary areas of research. LeVay’s brilliance, sustained immersion in this subject, and scientific acumen are on display throughout the volume; an accomplished neuroscientist and compelling writer, he demonstrates in this volume an exceptional capacity for the integration of an enormous array of scientific findings. He argues passionately and persuasively for a biological understanding of the etiology of sexual orientation. Nevertheless, there are subtle problems with this volume unlikely to be perceived by the reader who does not possess background in the primary literature. What are its strengths and strategic weaknesses?

LeVay demonstrates sophistication in outlining the nature of sexual orientation, and then provides an orienting sketch of his evolving theory. He examines differences in gender-related traits and behaviors in childhood and adulthood that appear to be associated with the continuum of straight to gay sexual orientation. He argues passionately for male homosexuality understood as a result of biologically-driven feminization, and for some lesbianism as the result of masculinization:

Homosexuality is a part of a package of gender-atypical traits. Some characteristics of the bodies and minds of gay men [including sexual attraction] are shifted in a female direction compared with straight men, and some characteristics of the bodies and minds of lesbians and bisexual women are shifted in a male direction compared to straight women (273).

He examines putative hormonal, genetic, brain, physical/morphological, and birth order contributions to the shaping of sexual orientation, examining variables that could be both cause and effect of final sexual orientation. His survey is comprehensive given the limits of a volume targeted for the (very) sophisticated general reader.

In addition to the incisiveness of his analysis and persuasiveness of his prose, LeVay is to be commended for his frequent cautions that global findings about sexual orientation do not yield explanations at the individual level for the emergence of sexual orientation (for example, “I also emphasize our inability to explain in any precise way why any particular individual becomes gay or straight” [xvii]), and his usual, but not consistent, caution in his discussion of the methodological limitations of the complex body of research cited.

Even so, it gave me pause to recognize that even LeVay gets things wrong sometimes. The most egregious example occurred when, in bringing his argument to a climax, he asserted: “Perhaps the strongest clue that probabilistic processes influence sexual orientation comes from monozygotic twins. If one such twin is gay, there are roughly even odds that the co-twin will be gay or straight” (282). This kind of error, amazingly common among those arguing for biological etiology, is conclusively refuted by the very literature that LeVay cites. Recent and superior studies point to much smaller monozygotic twin concordance. LeVay himself cites the best recent study, that of N. Långström,1 who found in a huge data set compiled from the national registry for twins in the nation of Sweden that of 71 monozygotic male twin pairs in which at least one co-twin was gay, in only 7 cases was the matching co-twin also gay. Thus, LeVay should have reported that “if one such twin is gay, there is roughly a 1 in 10 chance that the co-twin will also be gay.” This is a substantive error, especially if this is “perhaps the strongest clue.” I detected this error in his discussion of literature with which I am intimately familiar, recognition of which compromised my confidence in his accuracy of coverage of research with which I have less familiarity.

A second problem with the volume was LeVay’s tendency to employ creative explanations and alternative hypotheses to explain away findings inconsistent with his theory. In one place, he reviews the inconsistent evidence for the hypothesis that homosexual orientation is partially caused by a gay man having older brothers, and he explains away studies that failed to find the effect with an appeal to “methodological issues, atypical samples, or pure chance” (254). With some consistency, he only applies such logic to studies that do not bolster his theory. Similarly, when citing the meager and questionable literature suggesting that gay men have larger family sizes (siblings, cousins, aunts and uncles, thus defeating the claim that homosexual orientation could not have a genetic basis because its lack of reproductive advantage would result in its extermination), LeVay bolsters the one supporting study by dismissing the parallel disconfirming study, saying “this latter finding might have resulted from a recruitment bias” (183). This tendency to distill strong support from a conflicted literature by explaining away disconfirming studies crops up often throughout the volume.

The big problem with LeVay’s argument, however, is the inconsistent way he frames his theory. At a few points in the book he suggests that the core question is not whether there is a biological causal effect but rather what size is the biological effect. This is the right way to begin to frame the question, to which we must add the crucial second half of the question of what kinds of other variables contribute alongside the biological ones. Someone like myself can embrace that biology contributes to the causation of sexual orientation, even significantly, but can still argue about the size of that influence and the nature of other factors. I might read the literature and think that identifiable biological causes are 20% of the total etiological package, and LeVay might argue for 50 to 60%; the complementary question is how we are to understand the causative remainder. 

Throughout the book, LeVay, to my understanding, not only overestimates the power of identifiable biological etiological variables, but problematically attributes the unexplained remainder only to chance and various types of biological “static.” He frequently frames the argument as if the only two etiological theories are total biological causation or total environmental causation. At no point does he engage a true interactionist hypothesis where experiential variables (familial, peer, cultural) can interact with biology. He is unrelenting and emphatic in his resistance to any environmental variables having causal influence of any kind in concert with biological variables. Amazingly, he asserts, “there is no actual evidence to support any of those ideas” (271). Similar indefensible absolute assertions mar this work throughout. To the contrary, examples abound of significant sociocultural influences on sexual orientation.2

The other major problem in LeVay’s analysis is his failure, on a systematic basis, to reckon with the pervasive problem in this literature of unrepresentative samples. He recognizes this problem in certain areas, describing, for instance, how the initial (and highly publicized) report that gay men have a disproportionate ratio of counterclockwise hair whorls on the crowns of their heads has been utterly disproven by better studies of more representative samples. Unfortunately, the lesson learned is not systematically applied to other important research areas.

Most notably, he fails to contextualize earlier identical twin studies and earlier tests of the “older brother” hypothesis, both conducted on biased samples recruited through advertisements in the gay community, in favor of later, superior studies on representative samples. Regarding the very influential “older brother” hypothesis, LeVay treats as equivalent earlier studies conducted on advertisement-recruited gay samples, and later, ever more representative samples. My quick summary of this literature would be that the early, advertisement-recruited samples showed significant such effects. Then A. F. Bogaert3 analyzed two smaller nationally representative samples, finding an exceptionally weak “older brother” effect for only same-sex attraction (no effect for same-sex behavior), followed by his analysis4 of an enormous representative sample eight times the size of his previous studies, only to find the “older brother” effect had disappeared! The other latest studies, one of 2 million Danes5 and another of 10,000 American teenagers,6 also failed to find the effect. LeVay’s conclusion is “that gay men do have significantly more older brothers, on average, than straight men” (254). The better conclusion is that larger and more representative studies erode confidence that the “older brother” effect even exists. Much of LeVay’s other evidence cited in support of his theory likely suffers from similar problems with volunteer- and advertisement-derived samples of questionable representativeness. Might future research also see those putative effects shrinking in effect size?

Two final problems. First, throughout the book LeVay refers to “pre-gay” children, particularly “pre-gay boys.” This is one tangible place where his cautions that global findings about sexual orientation do not yield explanations at the individual level for the emergence of sexual orientation go out the window. It is indisputable that highly feminized boys and highly masculinized girls are, on average, more likely in adulthood to manifest homosexual orientation. But given that many such children never become gay or lesbian, to refer to atypical children as “pre-gay” strikes me as reckless. Such sentiments convey a sense of determinism that is unwarranted, and facilitates the many voices telling parents today, falsely, that gender-atypical children are going to become homosexual.

Finally, I was stunned by LeVay’s treatment of early sexual experience of children and adolescents. In discussing the influence of “one’s first sex partner,” he states that

[it may not be necessary] to assume that the children or adolescents were sexually passive targets for molestation by their elders. In reality, it is likely that many of them, especially the adolescents [and thus not excluding the pre-adolescents], already felt sexually attracted to same-sex partners. If so, they may have initiated the contact or responded willingly to the older person’s advances. (35)

Whatever he meant, to make a comment that appears to “blame the victim” for such early experiences seems unwise.

This book provides the most comprehensive and thoughtful review available of the scientific evidence for biological contributions to the etiology of sexual orientation. Read with discernment, it provides a helpful guide to this intriguing and contentious field.

Cite this article
Stanton L. Jones, “Gay, Straight, and the Reason Why: The Science of Sexual Orientation”, Christian Scholar’s Review, 41:2 , 214-217


  1. N. Långström, Q. Rahman, E. Carlström, & P. Lichtenstein, “Genetic and Environmental Effects on Same-Sex Sexual Behavior: A Population Study of Twins in Sweden,” Archives of Sexual Behavior 39 (2010): 75-80.
  2. See, for example, M. Frisch & A. Hviid, “Childhood Family Correlates of Heterosexual and Homosexual Marriages: A National Cohort Study of Two Million Danes,” Archives of Sexual Behavior 35.5 (2006): 533-547 or A. M. Francis, “Family and Sexual Orientation: The Family-Demographic Correlates of Homosexuality in Men and Women,” Journal of Sex Research 45 (2008): 371-377.
  3. A. F. Bogaert, “Number of Older Brothers and Sexual Orientation: New Tests and the Attraction/Behavior Distinction in Two National Probability Samples,” Journal of Personality and Social Psychology 84.3 (2003): 644-652.
  4. A. F. Bogaert, “ Physical Development and Sexual Orientation in Men and Women: An Analysis of NATSAL-2000,” Archives of Sexual Behavior 39 (2010): 110-116.
  5. Frisch & Hviid, “Childhood Family Correlates of Heterosexual and Homosexual Marriages.”
  6. Francis, “Family and Sexual Orientation: The Family-Demographic Correlates of Homosexuality in Men and Women.”

Stanton L. Jones

Stanton L. Jones is Provost at Wheaton College.