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Homosexuality - the causes...

winter 1997

From nucleus - winter 1997 - Homosexuality - the causes... [pp19-28]

What causes homosexuality? Is it genes, upbringing or simply a matter of personal choice? Peter Saunders reviews the literature and draws some interesting conclusions

Homosexuality - 'being sexually attracted only by members of one's own sex' according to the Oxford Dictionary. Unfortunately, behavioural scientists tell us that this definition is too simplistic. Sexuality is a complex matter: many people are not exclusive in their sexual inclinations. A classification system,[1] devised in the 1940s by Alfred Kinsey, rates an exclusively heterosexual person as Kinsey 0 and an exclusively homosexual person as Kinsey 6, the continuum between 0 and 6 covering varying degrees of bisexuality. In addition to this spectrum of preference, desire may not correlate with behaviour. Therefore, the term 'sexual orientation' is now used to describe a person's predominant sexual preference.

19th Century medics attributed homosexuality to moral degeneracy, mental illness and 'congenital anomaly'. The 20th Century has seen hormonal imbalance, psychosocial influences and biological factors named as possible suspects. The American Psychiatric Association cancelled homosexuality's pathological classification in 1974. Now that it has gained 'non-pathological status', it is increasingly hard to challenge the prevailing views on homosexuality's causation.

Bancroft, in a British Journal of Psychiatry editorial,[2] wrote, 'This is an area, par excellence, where scientific objectivity has little chance of survival'. It certainly is easy to bring preconceptions to scientific investigation. We are always tempted to view the facts selectively in order to verify our convictions. Researchers who have the added motivation of changing public opinion will be guided along certain channels in their work. Journalists can bring their private social agendas to bear by selective and sensational reporting of research findings. Tenuous conjecture is portrayed as certain conclusion to a gullible public. Of course, it's quite appropriate for the public to be responsibly informed about scientific discoveries; however, twenty-second sound-bites cannot do justice to complex controversies.

Equally, Christians have to be careful not to fall into the same trap; we must not selectively use scientific findings to bolster our own position. The biblical injunction to 'enquire, probe and investigate it thoroughly' (Deuteronomy 13:14) is good advice. As the Bible leads us to question our interpretation of scientific facts, so new discoveries may lead us to question whether we have interpreted the Bible correctly. Revelation and science need to be balanced in the humble search for truth; properly interpreted, they should not contradict one another.

The limitations of science

When the media next announce the discovery of another 'gay gene', we should evaluate the evidence before jumping to conclusions.

  1. Has the research been replicated elsewhere? For decades, researchers adopted Kinsey's reported figure of 10% for the general incidence of homosexuality. Kinsey's study had been poorly designed, using a non-randomly selected population, 25% of whom had been prisoners. The figures stood unchallenged until quashed by contemporary research; a figure of 1-2% is now generally quoted.
  2. What does the scientific community say? When it was announced that homosexual orientation had been mapped to a section of the X chromosome,[3] the press reported it as fact. However, a BMJ editorial[4] was far more cautious.
  3. Are there confounding variables which could be distorting results? A key study[5] claiming to prove that homosexuality has a genetic basis recruited subjects through homophile magazines: hardly an unbiased sampling process.
  4. Is the apparent link a direct effect or not? Does brain structure determine sexual orientation or vice versa? Is there a third factor involved such as AIDS?
  5. Is the proposed solution too simplistic? It is becoming clear that nature is far more complex than we first imagined. The lack of any real consensus should make us suspect that we are not dealing with simple cause and effect.

Nature or nurture?

Is homosexuality genetic or the result of upbringing? Is it biological or psychosocial? Are people 'born that way' or 'made that way by men'? (Matthew 19:12) If nature or nurture (or both) are involved, then what part does personal choice play in a person adopting a homosexual lifestyle?

Opinions differ widely among leading researchers. Boston psychiatrist Richard Pillard concludes that 'homosexual, bisexual and heterosexual orientations are an example of the biologic diversity of human beings, a diversity with a genetic basis'.[6] Van Wyk and Geist contend that 'biologic factors exert at most a predisposing rather than a determining influence'.[7]

Nature arguments

Those who advocate a biologic cause have argued that homosexuals possess different hormonal mechanisms, brain structure or genotype. Such biological explanations may not be unrelated as genes lay the blueprint for hormones which in turn influence body structure.

Hormonal mechanisms

At one stage it was thought that homosexuals were hormonally different. This idea was abandoned when sensitive hormone assays became available and accurate measurement could be made.[8]

Hormones might play a part in prenatal brain development and hence in sexual orientation. Female rats exposed to androgens and neonatally castrated male rats both exhibit sexual behaviour characteristic of the opposite sex.[9,10] Is the fetal rat's brain being hormonally programmed? Could the same sort of thing occur in human foetuses who later show homosexual tendencies? There are limits in extrapolating these rodent studies to man. Sexual behaviour in rats is under rigid hormonal control; human sex is not reflex but complex and conscious behaviour. The prenatal hormone theory doesn't explain the complexity and variability of the human sexual response with changes of erotic fantasies, modes of sexual expression and even sexual orientation over time. If the prenatal hormone hypothesis were correct, we would find a higher incidence of abnormal gonadal structure or function in homosexuals. We would also find a higher proportion of homosexuals with androgen level disorders. Extensive reviews of the literature suggest that this is not the case.[11,12] For example, there is no evidence that children resulting from hormonally treated pregnancies develop homosexual tendencies.[13]

Very rare medical conditions of ambiguous sexual status have been suggested as evidence for a hormonal cause of homosexual orientation. One example is testicular feminisation: affected individuals are genetically male, have normal intra-abdominal testes but apparently female external genitalia. They are psychosexually indistinguishable from heterosexual genetic females.[14] However, they are raised as females and so this research does not prove that sexual preference is hormonally programmed rather than environmentally conditioned.

Women with congenital adrenal hyerplasia have masculinised genitalia. The vast majority develop heterosexual interests and there is no consistent evidence for an increased incidence of lesbianism in this condition. Even if this were the case, it would be almost impossible to show that this was due to a hormonal effect on the brain rather than the psychological effect of having masculinised genitalia.

It needs to be stressed that over 99% of homosexuals have no measurable hormonal abnormality. The case for a hormonal cause of homosexuality remains unproven.

Brain structure

Could homosexuality be the result of differences in the structure of the brain? Again, studies in rodents have aroused suspicions. The rat SDN-POA hypothalamic nuclei group is sexually dimorphic. Could there be differences in human brains, not only between male and female but between heterosexuals and homosexuals?

In 1984, evidence was found for a sexually dimorphic hypothalamic nucleus;[15] however, a link between size and sexual orientation was not found.[16] In 1991, it was reported that the hypothalamic nucleus INAH3 was smaller in women and homosexual men than in heterosexual men.[17] This study was highly publicised but there were again reasons to be cautious. Firstly, the study numbers were small. Most of the homosexual men with abnormal hypothalamuses had died of AIDS. It was not apparent how the anatomical area involved could have had a bearing on sexual behaviour. Even if it did have an effect, it would remain to be proven that the structural change was the cause rather than the result of the altered sexual orientation. Other researchers have pointed to technical flaws in the study[18] and its findings.

The brain's commissures have been studied. In 1992, it was reported that the anterior commissure was smaller in heterosexual men than in heterosexual women and homosexual men.[19] Again, considerable overlap existed between the groups and the majority of the homosexuals had AIDS. The corpus callosum has been reported as being female-typical in homosexual men; so far, 23 studies have yielded conflicting results.[20]

Genetic studies

'Monozygotic twins are 'experiments' which nature has conducted for us, starting in each case with identical sets of genes and varying environmental factors.'[21] One way of studying twins is to find monozygotic twins (MZ) who were separated at birth; any behaviour they both exhibit is assumed genetic. Another approach is to compare dizygotic twins (DZ) to MZ twins; heritability can then be estimated.

Most twin studies of homosexuality, however, are merely anecdotal accounts of concordant (both twins are homosexual) or discordant (only one twin is homosexual) twins.[22] Studies of two pairs of MZ concordant lesbians were performed in 1967[23] and 1973.[24] Between 1964 and 1980, four other sets of researchers looked at six pairs of discordant MZ male twins.[25,26,27,28] There is only one study, performed in 1986, of homosexual MZ twins reared apart;29 four female and two male pairs were studied. It was concluded that genetic factors were hard to deny in male homosexuals, but less important in lesbians. However, sample size was small.

There have also been few studies comparing MZ and DZ twins. The first was done by Kallman in 1952; it provided the first 'hard-evidence' for a genetic basis for homosexuality. Kallman recruited twins from psychiatric, charitable and correctional institutions; he also used 'direct contacts with the clandestine homosexual world'.[30] He gave this biased population Kinsey ratings from 3 to 6. He claimed that the concordance was 100% in MZ twins but only 12% in DZ twins. Kallman's results have never been reproduced; he later admitted that the 100% MZ concordance was a statistical artefact.[31]

Two studies were done in 1991, the second one being widely reported in the popular press. The first mailed questionnaires from which both zygosity and sexual orientation were determined! The large sample was highly selected and ranged from impressionable nineteen year olds to stable forty year olds. The authors declared more homosexual MZ than DZ twins.[32] However, they used questionable methods of statistical analysis: Chi-squares and t-tests were inappropriately applied. In his excellent review of the evidence, McGuire reanalysed the data and found no differences between the groups![33] The second, more famous study looked for differing concordance rates between twins and adopted brothers. All subject recruitment was through homophile publications. Again, zygosity and Kinsey rating were self-assessed by questionnaire. Using ratings derived from questionnaire responses, the concordance rate for MZ twins was 50%. The DZ twin concordance was less than this and not significantly different from that of adopted brothers. There are many problems with this study; indeed, the fact that biological and adopted brothers show the same incidence of homosexuality actually suggests an entirely environmental origin.[34]

The most recent twin study in 1992 investigated factors within a twin pair that might lead to homosexuality. This study shared all the problems of the previous ones. Although its data are no stronger than those in the other studies, it is perhaps ironic that it found no evidence for a genetic origin. Indeed, the authors state, 'More detailed exploration of the sexual relationships between twins and their later development may cast more light on the origins of sexuality than a narrow search for genetic factors'.[35]

There have been few systematic family studies of homosexuality; like the twin studies, most are anecdotal. However, there are three worth looking at. In 1981[36] and 1986,[37] Pillard presented the two largest family studies to date. Both shared many subjects, again mostly recruited through homophile newspapers. Homosexual men gave information about their siblings whose sexual orientation was then rated in four different ways. Some non-cooperative siblings were included using second-hand evidence! A more serious problem is the conflicting definitions of sexual orientation. An index case with a Kinsey rating of 2 was classed as heterosexual; if he was a sibling, he was apparently bisexual!

In a blaze of publicity in 1993, Hamer claimed to have found a maternal inheritance pattern for male homosexuality.[38] He apparently found five X-chromosome markers, leading to talk of an X-linked homosexuality 'gene'. Unsurprisingly, an article in Nature commented, 'Were virtually any other trait involved, the paper would have received little public notice until the results had been independently replicated'.[39] More homosexual maternal male relatives than homosexual paternal male relatives were reported. Once more, this conclusion was reached using statistical tests that other researchers consider inappropriate. As with the twin study, McGuire reanalysed Hamer's data and stated, 'Using the more appropriate test, I compared similar pairs of relatives...there is no evidence for a maternal effect'. There are also problems with the data used in the linkage study. The general population frequency of the sequence involved, Xq28, is not yet known. McGuire concluded, 'Until these results are replicated...they should be viewed with extreme scepticism'.[40]

Most recently, in 1995, two scientists made a highly publicised announcement that a gene transplanted into fruit flies produced homosexual behaviour![41] It later transpired that these flies were actually bisexual and that no lesbian flies had been produced. As discussed earlier, we should beware of comparing human and animal sexual responses.

Overall, there is some evidence that genes may have some bearing on the emergence of a homosexual orientation. However, many questions remain. Why do large proportions of MZ twins vary in their sexual orientation? Why does sexual preference change over time or with therapy?[42] Clearly we are not dealing with a simple causal link. While we may not ever find a gay gene as such, there is increasing evidence to suggest that personality variants (eg novelty seeking and harm avoidance) may well be inherited.[43] These could predispose to the development of a homosexual orientation within a certain environment.

Writing in the Journal of Homosexuality, McGuire concludes, 'Any genetic study must use:

  1. Valid and precise measures of individual differences
  2. Appropriate methods to ascertain biological relationships
  3. Research subjects who have been randomly recruited
  4. Appropriate sample sizes
  5. Appropriate genetics models to interpret the data.

To date, all studies of the genetic basis of sexual orientation of men and women have failed to meet one or more or any of the above criteria'.[44]

Nurture arguments

The pure biological view is that homosexual orientation is programmed in the genes, fashioned by hormones and displayed in brain structure. The pure psychosocial view is that the environment writes upon the developing child as one draws lines on a blank sheet of paper. As with the biological arguments, the nurture arguments will be considered under several headings, although they interrelate.

The cultural environment

The cultural view is that sexual conduct is determined by society. Whereas biological sex is set at birth, gender-specific behaviour develops in a cultural context. Tradition, religious belief and political factors lay a framework for acceptable behaviour which eventually feels natural. The diversity of sexual behaviour across cultures and history provides evidence for this view. There are cultures where homosexual behaviour is so uncommon that there is no word for it in the language.[45] Indeed, open long-term relationships between consenting adults were almost unheard of in Western culture before the 19th century.

The family environment

Most nurture theories focus on the parent-child relationship. Male homosexuals often have a dominant, supportive mother and a weak, remote or hostile father.[46] Lesbians may have had a dysfunctional mother-daughter relationship. This view has been popularised by Elisabeth Moberly who believes that homosexual orientation is the result of unmet same sex-love needs in childhood.[47]

Martin Hallett, Director and Counsellor at True Freedom Trust, has found that the majority of male homosexuals counselled identified very much with this lack of intimate bonding with the father or any other male role model.[48] The heterosexual identity is not established and the unaffirmed child later suffers from a lack of confidence and fear of failure in heterosexual contacts. He tries to meet his unmet same-sex needs through sexual relationships. Sara Lawton,[49] a Christian counsellor specialising in lesbianism and sex-abuse, sees the root of female homosexuality as an unmet need for mother love which becomes sexualised in the adult and may be compounded by repressed trauma such as adoption and sexual abuse.

The parent-child relationship can also be disturbed through death or divorce. Saghir and Robins found that 18% of homosexual men and 35% of lesbians had lost their father through death or divorce by the age of ten. The figures for heterosexuals were 9% and 4% respectively.[50] Up to 70% of homosexual adults describe themselves as having been 'sissies' or 'tomboys' as children;[51] still, most adult homosexuals do not fit the effeminate male or masculine female stereotype.

The peer group environment

Forming homosexual identity takes time. Most pre-pubertal children consider themselves heterosexual and are reinforced in this by peer-group pressure. For the child who doesn't 'fit in', the masculine female or the non-masculine male, identification with the opposite sex peer group may prove easier. This can lead to gender confusion in adolescence and identification with others of the same sex who are suffering from the same feelings of isolation. The acceptance of the homosexual label can then bring a measure of security, self-understanding and acceptance.

'Coming out' - identification with the gay culture - has many rewards in terms of escaping from conflict, reducing the pain of rejection and providing human contact. A network of supportive friends and perhaps a long-term homosexual relationship can be powerful forces driving people into and keeping them within the gay community. The issue of heterosexual recruitment into homosexuality is complex. However, promotion of the idea that homosexuality is a genetically-determined normal variant will certainly lessen any stigma and make it easier for those with confused gender identity to enter the 'gay community'.

The moral environment

A child's conscience is largely shaped by parental environment and can be underdeveloped or blunted, especially if the public conscience itself is changing. When homosexuality was regarded as degeneracy, there were powerful social pressures preventing its expression. Now that one can be lambasted for suggesting that homosexuality is abnormal, the tables have turned. Bancroft stated, 'It is difficult, on scientific grounds, to avoid the conclusion that the uniquely human phenomenon of sexual orientation is a consequence of a multifactorial developmental process in which biological factors play a part but in which psychosocial factors remain crucially important'.[52]

The role of personal choice

Some react against nature or nurture models, arguing that sexual orientation is a myth and homosexuality is simply a choice. All of us sense that we have some responsibility for our destiny. We are not solely genetic machines anymore than we are blank slates on which experience writes. At some point, every practising homosexual makes a choice to indulge in homosexual fantasy or to have gay sex. However, we must not make the mistake of ignoring the role of nature and nurture in making those of homosexual orientation what they are.

While there will always be those who support one sole model of causation, most concede that many factors are involved. Heredity, environment and personal choice all play a part. This should leave us with a humble and open attitude, willing to learn more from scientific research and the testimony of skilled counsellors and gay people.

What is natural?

There is often an unstated assumption that strong feelings should determine behaviour; in fact, this is not accepted in almost any other area of life. We don't believe that envy sanctions stealing or that lust legitimises adultery. Proverbs 14:12 says, 'There is a way that seems right to man but in the end it leads to death'. The Gay Rights lobby presupposes that what comes naturally is good. By contrast, the Bible's view is that the whole world and human beings themselves are polluted by sin which has affected our bodies (genes included), minds, wills and feelings. Consequently, our biology, thoughts, choices and desires are not what they were intended to be. In the biblical scheme, 'natural' (as in Romans 1:27) means not 'what comes naturally' but rather 'what God intended (and intends) us to be'.


  1. Kinsey A et al, Sexual behaviour in the human male, WB Saunders, 1948
  2. Bancroft J, British Journal of Psychiatry, 1994, 164:437-440
  3. Hamer D et al, Science, 1993, 261:321-327
  4. Baron M, BMJ, 1993, 307:337-338
  5. Bailey J and Pillard R, Archives of General Psychiatry, 1991, 48:1089-1096
  6. Pillard R and Bailey M, Psychiatric Clinics of North America, 1995, 18(1): 71-84
  7. Van Wyk P and Geist C, Archives of Sexual Behaviour, 1984, 13:505-544
  8. Meyer-Bahlburg H, Progress in Brain Research, 1984, 61:375-398
  9. Goy R and McEwen B, Sexual differentiation of the brain, Cambridge, Mass: MIT Press, 1980
  10. Meyer-Bahlburg H, Archives of Sexual Behaviour, 1977, 6:297-325
  11. Meyer-Bahlburg H, Archives of Sexual Behaviour, 1979, 8:101-119
  12. Byne W and Parsons B, Archives of General Psychiatry, 1993, 50:228-239
  13. ibid
  14. Money J, Psychoneuroendocrinology, 1984, 9:405-414
  15. Swaab D and Fliers E, Science, 1985, 228:1112-1114
  16. Swaab D and Hofman M, Dev Brain Research, 1988, 44:314-318
  17. LeVay S, Science, 1991,253:1034-1037
  18. See reference 12 above
  19. Allen L and Gorski R, Proceedings of the National Academy of Sciences, USA, 1992, 891:7199-7202
  20. See reference 12 above
  21. Price B, American Journal of Human Genetics, 1950, 2:293-352
  22. McGuire T, Journal of Homosexuality, 1995, 28(1-2):115-45
  23. Pardes H et al, The Psychiatric Quarterly, 1967, 41:108-133
  24. Perkins M, Behaviour Genetics, 1973, 3:387-388
  25. Parker N, British Journal of Psychiatry, 1964, 110:489-495
  26. Klintworth G, Journal of Nervous and Mental Disease, 1962, 135:113-125
  27. Zuger B, Comprehensive Psychaitry, 1976, 17:661-669
  28. McConaghy N and Blaszczynski M, Archives of Sexual Behaviour, 1980, 9:123-31
  29. Eckert E et al, British Journal of Psychiatry, 1986, 148:421-425
  30. Kallman F, Journal of Nervous and Mental Disease, 1952, 115:283-298.
  31. Kallman F, Psychosomatic Medicine, 1960, 22:258-259.
  32. Bailey J et al, Behaviour Genetics, 1991, 21:75-96.
  33. See reference 22 above
  34. See reference 22 above
  35. King M and McDonald E, British Journal of Psychiatry, 1992, 160:407-409.
  36. Pillard R et al, Archives of Sexual Behaviour, 1981, 10:465-475
  37. Pillard R and Weineich J, Archives of General Psychiatry, 1986, 43:808-812
  38. See reference 3 above
  39. King M, Nature 1993, 364:288-289
  40. See reference 22 above
  41. Thompson L, TIME Magazine, 1995, 12 June:52-53
  42. Masters W and Johnson V, Little, Brown and Co., 1979
  43. Cloninger C, Archives of General Psychiatry, 1987, 44:573-588
  44. See reference 22 above
  45. See reference 2 above
  46. Bell A et al, Sexual preference: its development in men and women, Bloomington: Indiana University Press, 1981, pp41-62, 117-134
  47. Moberly E, Theology, 1980, p83
  48. Hallett M, Nucleus, January 1994, pp14-19
  49. Lawton S, lecture 8 in Signposts to Wholeness, True Freedom Trust, 1994
  50. Saghir M and Robins E, Male and female homosexuality: a comprehensive investigation, Baltimore: Williams Wilkins, 1973
  51. See reference 25 pp17-31, 191-203
  52. Schmidt T, Straight and narrow? Compassion and clarity in the homosexuality debate, IVP, 1995, p215

Article written by Peter Saunders

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