How much is known about the origins of homosexuality?

23 July 2008

A great deal of scientific evidence has now become available, says Michael King

Alternative? A eucharist to celebrate the gifts of gay people, held at St Stephen’s Field, Canterbury, near the Lambeth Conference last Sunday. The Rt Revd Gene Robinson attended (front, left) AP

Alternative? A eucharist to celebrate the gifts of gay people, held at St Stephen’s Field, Canterbury, near the Lambeth Conference last Sunday. The Rt...

AS the debate about homosexuality in the Anglican Communion becomes ever more intense, it may be helpful to consider a number of its premises. Many Christians, as well as people with no spiritual beliefs, may be confused by claim and counterclaim about whether gay and lesbian people choose their sexual orientation, and whether they can become heterosexual.

Last year, the Royal College of Psychiatrists’ submission to the Anglican Communion’s listening exercise was published (News, Comment, 16 November 2007). Although it was generally well received, there were concerns in some quarters that appeared to arise from a misunderstanding about the origins of homosexuality and same-sex behaviour.

Like all complex human characteristics, evidence on the origins of sexual orientation is difficult to obtain and to interpret. This is because it involves study of human development from the embryo to the adult, of brain structure and function, physiological processes, and of evolutionary and psychological theory.

In addition, the hunt for evidence has been influenced by a long-held assumption that homosexuality is abnormal. Thus research has traditionally focused on why and how it occurs rather than examining how our sexual orientation (heterosexual or homosexual) arises and is sustained. One might say we know less about the determinants of sexual orientation than we know about gender, but more than we know about personality.

THERE ARE eight areas about which we now know a great deal, but with some varying degrees of certainty.

1. Normality: homosexuality is now regarded as a human characteristic rather than a disorder. It has been removed as a diagnosis from all international classifications of diseases.

Two decades ago, Professor John Bancroft, an esteemed sexologist who later became director of the Kinsey Institute in Indiana, concluded that homosexuality was compatible with normal health and well-being (“Homosexuality. Compatible with full health”, British Medical Journal, 1988; 297).


Churches of all mainstream denominations agree. The homosexual person is not condemned, even if same-sex behaviour is not permissible.

2. Becoming aware: there is now considerable evidence that gay and lesbian people become aware of their sexual orientation at about puberty. They often describe feeling different from other children, before becoming fully aware of their sexual feelings. There is no sensation of having or making a choice in the matter.

Also, it is difficult to imagine why a proportion of young people in every generation throughout history would make a choice to adopt a sustained pattern of sexual behaviour that was often accompanied by childlessness, and that still, in many parts of the world, meets vigorous social discrimination.

3. A continuum of sexuality: like most human characteristics, sexual orientation appears to form a spectrum, with heterosexuality at one end and homosexuality at the other. People across the middle of the spectrum experience a range of heterosexual and homosexual responsiveness, and are often referred to as bisexual.

4. The genesis of sexuality: sexual orientation is formed very early (early childhood or before), and involves genetic factors. Although no specific genes for male homosexuality have been identified, identical twins are more likely to be both gay than brothers, and homosexuality in men is more often inherited through the mother’s line (Savolainen V., Lehmann L., “Evolutionary biology: genes and bisexuality”, Nature 2007; 445).

Homosexuality is not, however, fully heritable: one member of an identical twin pair may be gay or lesbian, and the other heterosexual. Genes are not the only factors involved, and environmental influences may be needed for genetic effects to be expressed.

5. Gene-environment interactions: environmental factors that interact with genes to produce human characteristics may be biological, psychological, or socio-cultural. They may act during gestation, or in the early years of life.

Examples of such interactions are that a gene predisposing to obesity will be expressed only in societies with abundant food; or that development of language skills in early life will occur only in an environment where words are spoken and heard.

6. Environmental factors: environmental contributions to the formation of human characteristics usually occur at so-called critical periods in early development. They also tend to be irreversible. For example, if language is not learned during the early years of life, it may not be possible to develop it properly thereafter. If vision is impaired for the first ten years of life, its restoration may not lead to normal sight.


Although we are unsure what those environmental factors might be, we know what they are not: for example, people do not become homosexual or heterosexual because of a particular kind of parenting or because of any kind of early sexual experience.

The most solid evidence about environmental factors is that gay men have more older brothers than straight men (Cantor, et al., “How many gay men owe their sexual orientation to fraternal birth order?” Archives of Sexual Behavior, 2002; 31).

7. Do people of different sexualities have different brains? There have been many reports of differences in brain structure between homosexual and heterosexual people, but very few have held up to consistent verification.

Many have reported similarities between the brain structures of gay men and heterosexual women, as well as those of lesbians and heterosexual men. Unfortunately, this approach often conflates sexual orientation with aspects of gender, which is misleading. Moreover, the evidence can be used to support arguments that sexual orientation is innate and developmental, or that homosexual activity leads to brain changes.

8. Is sexual orientation malleable? There is abundant evidence that people who identify themselves as heterosexual can respond to same-sex partners when opposite-sex partners are not available, for example in same-sex institutions. Similarly, many gay or lesbian people may have opposite-sex partners when trying to conform to a heterosexual lifestyle.

However, attempts to change a person’s fundamental sexual orientation by psychological or medical means have not met with success. Furthermore, psychologists and doctors who attempted such treatments in the 1960s and 1970s became alarmed by the potential harm they were causing (King M., Smith G., Bartlett A., “Treatments of homosexuality in Britain since the 1950s”, British Medical Journal 2004; 328).

One or two recent studies of gay people (mostly men) who have undergone “reparative therapy” in the United States (a psychological approach that focuses on early relationships with parents and involves spiritual healing) have indicated that a very small proportion achieve change in their sexual orientation.

The authors of these reports, however, acknowledge their limitations (Archives of Sexual Behavior, October 2003). The patients studied were not randomised to the therapy or a control group, but consisted simply of volunteers who provided self-reports at various intervals after finishing therapy. Furthermore, most of the people who achieved change in their sexual orientation were bisexual when they began therapy, and none of the claims of change were supported by independent accounts of partners or family members.


The conclusion reached by scientists who have investigated the origins and stability of sexual orientation is that it is a human characteristic that is formed early in life, and is resistant to change. All theological, philosophical, and moral debates about how lesbian and gay people should lead their lives and follow their religious beliefs need to take account of these premises.

Scientific evidence on the origins of homosexuality is considered relevant to this theological and social debate because it undermines suggestions that sexual orientation is a choice.

As scientists, we welcome research into the origins and development of human sexuality. Unfortunately, scientific evidence is seen as relevant here because of homosexuality’s persisting image as a deviation from nature’s heterosexual template.

Dr Michael King is Professor of Primary Care Psychiatry at the Royal Free and University College Medical School, University College, London.

How objective is the Royal College of Psychiatrists’ view of the evidence? The Special Interest Group for Gay and Lesbian Mental Health in the Royal College of Psychiatrists was established to assist the College with scientific and clinical issues relating to homosexuality. It has 462 members (out of a total College membership of 13,627), whose sexuality is not asked about or known.

It accepts the view, which is widely held in the scientific community, that homosexuality is a normal variant of sexual orientation. It also supports psychiatrists and other mental-health professionals who may be discriminated against because of their sexual orientation.

Like other similar special-interest groups in the College, it is not a lobby group. When a woman or a black person makes a comment on gender or race issues, it is respected and even judged more important than if it were made by others. Discrediting a scientist’s view on homosexuality because he or she is gay or lesbian is another example of how homosexuality itself is denigrated.

Why is the evidence about homosexuality debated so strongly? Vigorous debate and criticism is an essential part of science. All scientific knowledge is open to doubt, and every hypothesis is held only until it is supplanted by a better one. However, the issue of homosexuality is further complicated by moral, ethical, and theological disagreements about its status in human beings. Thus it is hardly surprising that evidence about its origins is questioned.

Unfortunately, this means that empirical evidence can be used rather like biblical texts to argue that homosexuality is a normal variant on the spectrum of sexual orientation, a biological abnormality, a moral/immoral choice, or whatever else.

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