HOMOSEXUALITY - An Analysis of Biological Theories of Causation

Dr . Tahir I jaz, M.D., Winnipeg, Canada

Genetic Studies

Hormonal Studies

Neuroanatomic Studies


An indisputable and universal fact about humanity is that every-one owes their existence to the union between their father and mother. This forms the basis for the family, the social unit of society . However, homosexual behaviour also has been known to be present in some societies throughout history in varying degrees of prevalence . Over the past thirty years or so, such behaviour has become increasingly mainstream and open. Many people have started to consider such sexual behaviour to be the identifying characteristic of those who practice it. Homosexuality has stopped being what people do and has become who they are.[1]

Today, people practising homosexual lifestyles seek tolerance and acceptance from society at large, and have achieved considerable success. By organising themselves into a political movement, homosexuals vigorously lobby psychiatric, legal, and political organisations for changes in discrimination laws to include sexual preference, and seek such things as the right to adopt children, and health, pension and tax benefits enjoyed by legally married heterosexual couples.

The central theme vital to their political agenda is the idea that homosexual behaviour is an "innate" characteristic, perhaps genetic, like race or gender . Hence, according to these homosexual organisations, all moral connotations regarding their behaviour have to be dropped. They claim to be "born that way - " linkage of their behaviour to biologic causes is politically necessary, since that credo is what cements the homosexual rights groups' self-identification with genetically determined groups, like blacks and women.[2]

The increasing claims of being "born that way" parallels the rising political activism of homosexual organisations, who politicise the issue of homosexual origins . In the 1970s, approximately ten percent of homosexuals claimed to be "born homosexual" according to a large scale survey.[3]

However, in a survey in the 1980s, with the homosexual rights movement increasingly becoming active, thirty-five percent claimed to be born that way.[4]

Many scientists have claimed that homosexuality is rooted in biology, and much of the research has been conducted by scientists living a homosexual lifestyle[5]. In recent years attention has been given to the area of genetic, hormonal or neuroanatomic basis for homosexuality. An overview of the biologic theories on its causation is presented with an analysis of some of the studies It should be mentioned here that in contradistinction to these biologic theories, there is evidence to suggest that homosexual behaviour represents a socio-cultural phenomenon of learned behaviours and attitudes which are shaped by a society that increasingly tolerates, encourages and even glorifies sexual experimentation and adventurism - so much so, that even young children are victims in the form of sexual abuse. A full discussion of these complex social factors requires a separate article.

Before making an analysis of various studies purported to show a biologic or genetic basis for homosexuality, a few general comments should be made.

(a) Of all animals, human beings are the most genetically indeterminate. In the words of Dr. Joseph Wortis, Department of Psychiatry, State University of New York: "no complex high-level behaviour of the human species can be reduced to genetic endowment, not language, not house-building and not sexual behaviour[6] "Preferential and exclusive homosexuality is not naturally found in any infrahuman mammalian species[7] and it would be odd for such behaviour in humans to be genetically determined.

(b) Natural selection, the mechanism of evolution, also makes genetic theories problematic. In natural selection, advantageous traits, encoded in genes are passed on generation to generation and increase in prevalence. If the trait is deleterious, it should decline and disappear. Homosexuals, needless to say, have reduced reproduction, and should have disappeared long ago if there was a genetic basis[8].

(c) Another factor which makes genetic theories implausible are cultural considerations relating to attitudes towards homosexual behaviour. The prevalence of such behaviour increases in cultures indifferent to such behaviour, and a casual attitude towards sex in general. For instance in ancient Graeco-Roman culture, homosexual behaviour was tolerated and was highly prevalent[9] , whereas in cultures in which it was disapproved of, homosexuality was much more rare[10]. Dr. Baron, from the Department of Psychiatry, Columbia University, New York, commented in the British Medical Journal recently that " it would be difficult to envisage a change in the prevalence of a genetic trait merely in response to changing cultural norms[8] ."

(d) Also difficult to reconcile with biologic theories is the fact that ex-homosexuals exist - people who have given up such behaviours. Some have even formed groups such as Homosexuals Anonymous to offer counselling and encouragement for people wishing to change their habits. If homosexual preference is "in the genes" like human racial characteristics like skin colour, change could not be possible.

It is clear that sexual preference is not an immutable phenomenon. Preference and attitudes shift over time, and individuals cannot be simply categorised as homosexual or heterosexual. These shifts in sexual tastes of individuals show that homosexuality may be adopted by people who are confused, sexually adventurous, and rebellious, and has nothing to do with biologic determinism.

The evidence to show that sexual preference is flexible, not immutable, comes from published surveys of sexual behaviour patterns in the sociologic literature. Studies from the Family Research Institute and Kinsey Institute show that the majority of those currently homosexual, previously had sexual relations with the opposite sex, the majority of homosexuals had current sexual attraction to the opposite sex, and one to three percent of heterosexual adults actually considered themselves ex-homosexual[11] . Such studies identify homosexuality as a habit and preference, and not an inevitability.

Many leading clinical psychologists and psychiatrists (for example, Masters and Johnson, Bieber, Barnhouse, Socarides, Cappon, Hadden, Rubinstein, Leif) have reported very high success rates in helping individuals change their homosexual lifestyle. The American Medical Association Council on Scientific Affairs policy report distributed in 1981 and subsequent years states:

"There are some homosexuals who would like to and probably could change their sexual orientation. Because some homosexual groups maintain contrary to the bulk of scientific evidence that preferential or exclusive homosexuality can never be changed, these people may be discouraged from seeking adequate psychiatric consultation. What is more deplorable is that this myth may also be accepted by some physicians...The physician who is not alert to the orientation of the homosexual patient may not challenge the belief in sexual irreversibility and arrange for appropriate referral[12]." It is possible that the Council on Scientific Affairs of the American Medical Association may review its policies due to lobbying by pro-homosexual organisations.

1. Genetic Studies

(a) One of the most frequently cited studies of homosexuality was that of Kallmann in 1952[13]. He reported a one hundred percent concordance in identical twins for homosexuality, and only twelve percent concordance in fraternal twins (identical twins result from a fertilised egg splitting in half and each half continues to grow as an embryo. Thus, the identical twins have an identical genetic code. Fraternal twins do not have identical genetic codes as each twin arises from different fertilised eggs). Subsequent studies have failed to repeat Kallman's findings. Kallman later himself postulated that this impressive concordance was an artefact due to the fact his sample was largely drawn from mentally ill, institutionalised patients[14] .

The largest twin study was published by Bailey and Pillard[15] and received considerable media coverage. This study included fifty-six pairs of identical twins, fifty-four pairs of fraternal twins, one hundred and forty-two non-twin brothers of twins and fifty-seven pairs of adoptive brothers. They found that the concordance rate of homosexuality for genetically unrelated adoptive brothers was eleven percent, and for non-twin biologic brothers about nine percent. The rate for fraternal twins was twenty-two percent and for identical twins it was fifty-two percent. The fact that fraternal twins of homosexual men were twice as likely to be homosexual as other biologic brothers shows environmental factors are involved, since fraternal twins are no more similar biologically than are other biologic brothers. If being a fraternal twin exerts an environmental influence, it does not seem surprising that this should be even truer for identical twins, who the world thinks of as "the same", and treated alike and often mistaken for each other. The increased concordance can thus be entirely accounted for by the increased similarity of developmental experiences[16]. Furthermore, the fact that the concordance rates were similar for non-twin biologic brothers and genetically unrelated adoptive brothers is at odds with a simple genetic hypothesis, which would predict a higher concordance for biologic siblings[17].

A factor that may have had a drastic affect on the results of this study (and other similar studies) is ascertainment bias. Bailey and Pillard did not simply study a random sample of homosexuals; they were recruited through advertisements placed in homosexual publications. This method can be deemed questionable because it is highly dependent on the readership of those publications and on the motives of those who opt to respond. It may thus lead to skewed results - for example, inflated rates of concordance in identical twins owing to preferential participation[18] .

There are other technical flaws which are difficult to avoid in this area of research and make interpretations difficult. The phenotype in question, such as homosexual preference can be variable and difficult to define. How to categorise and define behavioural phenotypes is far from clear[18]. One must also note that behavioural twin studies gain their validity only by comparing the adult behaviour of twins reared in different environments. No study of twins reared together will be able to tease apart and quantify the different contributions, if any, of genetic and environmental factors[17].

Other studies such as by King and McDonald found similar concordance rates of homosexuality in identical and fraternal twins (ten percent and eight percent, respectively), seemingly at odds with a genetic hypothesis[19]. Of course, similar methodological problems apply as with other twin studies.

In summary, it is difficult to reach conclusions from twin studies published to date. Most studies have a small sample size and/or contain technical flaws in study design and methodology. Some studies suggest a genetic basis, while others do not. As Byne and Parsons note[17], what is intriguing in twin studies that have been published is the large proportion of identical twins who are discordant for homosexuality despite sharing not only their genes but also their prenatal and familial environments.

(b) In 1993, a genetic study was reported showing a significant correlation between declared homosexuality in forty pairs of brothers and inheritance of a genetic marker on the X-chromosome[20] . The report received considerable media coverage with extravagant claims of "gay genes discovered", although the researchers were careful not to make such claims in their paper. Similar past linkage studies of complex behavioural traits such as manic depression have not been replicated by other investigators, and hence has diminished support. Thus as articles in the British Medical Journal8, Nature[21], and Science[22] , point out, these findings have to be interpreted cautiously. This study will have to be repeated by other investigators and more information is required utilising other types of study designs to determine the frequency of the purported genetic marker in the general population[23] .

2. Hormonal Studies

(a) A popular belief which fell into disfavour in the late 1970s was the idea that sexual preference is determined by hormone levels. The development of new sensitive hormonal assays now in use fail to show any constitutional chemical differences between homosexuals and heterosexuals[24]. Furthermore, alteration in hormone levels in adults by surgical removal of the gonads or hormone injections has failed to induce shifts in sexual preference.

(b) A number of investigators have suggested that hormonal alterations during prenatal life may influence sexual preference in humans and use data from rat and guinea pig experiments to support their claim. The experiments conducted describe the interaction of sex hormones on the developing brain, particularly the region known as the hypothalamus. For instance, when female rats are administered male hormones pre-natally, they exhibit male sexual behaviour during adulthood. Similarly, when male rats are pre-natally administered a steroid drug to counteract the self-produced male hormone, the animals exhibit female sexual behaviour.

Some scientists have extrapolated these observations to humans and have theorised that homosexuality may originate due to similar pre-natal hormonal derangements. However, the rodent model of human homosexual behaviour has serious flaws, and extrapolation of rodent behaviour observations to psychological processes in humans is difficult. The rodent behaviours described are mating postures which are under rigid endocrine control and reflex-like, and may be induced, for example by a touch from a researcher's hand. Such posturing can be inhibited by blocking certain hormone receptors, and the frequency of such mating postures which a rat may assume over a period of time is related to the level or number of certain hormone receptors[17]. Motivated sexual behaviours in humans are not under such rigid endocrine control, rendering the rat model questionable. Such a hormonal theory also cannot explain the shifts in sexual preference humans may have over time. Furthermore, in human syndromes involving pre-natal male hormone deficiency in males or excess male hormones in females during pre-natal life (either as a result of drugs given to the mother or a genetic condition), there is no evidence of predisposition to homosexuality[17]. These facts show that in humans, learning and socio-cultural influences plays the role and not biologic pre-determinism.

(c) In female rodents the hormone oestrogen acts on the hypothalamus and exerts negative and positive feedback on the release of a hormone known as luteinizing hormone (LH). Low levels of oestrogen inhibits LH release (negative feedback) and high levels trigger LH release (positive feedback). In male rodents oestrogens only exert a negative feedback on LH release. Administration of oestrogen to normal female rats and castrated male rats at birth will result in an LH surge. However, an LH surge will not occur with oestrogen administration in adult females given male hormones at time of their birth or males castrated as adults. Thus it is believed male hormones have an affect on the developing rat brain and abolishes the ability of oestrogen to exert positive feedback on LH release. Two groups of researchers in the 1970s and 1980s claimed to find stronger feedback affect in homosexual men than heterosexual men, postulated to be from deficiency of prenatal hormones[25] , [26].

The difficulty again, however is extrapolation of hormonal controls in rats to humans, and primates in general. There is laboratory evidence that the rat model of oestrogen-hypothalamus interactions do not apply to humans and primates[27], [28], [29], [30] and in contradiction to previous studies, no correlation was found between the magnitude of the feedback effect of oestrogen and human sexual preference in subsequent studies[27] ,[31]. Previous studies showing evidence of differences in hormonal feedback affects in homosexuals and heterosexuals reflect experimental artefacts and possible differences in testicular function due to drugs, alcohol, or ageing which were not controlled for [17].

3. Neuroanatomic Studies

(a) In 1991, a report was published claiming that an area of the hypothalamus known as INAH3 is smaller in homosexual men and heterosexual women[32]. The report received immense media coverage. The study was conducted on brain tissues from cadavers Included were nineteen homosexuals, sixteen presumed heterosexual men, and six presumed heterosexual women. A number of factors make interpretation of the study difficult. Sexual histories were inadequate and a significant proportion of the subjects were presumed to have a certain orientation. All of the homosexuals died of AIDS, while only six of the presumed heterosexual men group died of AIDS. One can propose a hypothesis that the human immuno-deficiency virus (HIV) could affect brain tissue including the hypothalamus, and since reduced testosterone (a male hormone) has been documented to occur in patients with AIDS, this may be one of the mechanisms. Certain medications like antifungals administered for the treatment of infections can affect the hypothalamic-pituitary axis, but inadequate medical information is supplied in the study. Heterosexuals with AIDS often receive inferior medical care than homosexuals with AIDS as they more often are intra-venous drug users. This may also affect the results of the study, as the heterosexuals with AIDS may have had a different disease course and died at an early stage of infection[17]. Moreover, the area of the hypothalamus in question was larger in some of the homosexuals than in many of the heterosexuals, and smaller in some of the heterosexuals than many of the homosexuals. Hence, one cannot determine someone's sexual preferences by looking at his/her hypothalamus[1].

(b) A group of researchers recently published a study claiming that a brain structure known as the anterior commissure is larger in women and homosexual men than in heterosexual men[33] . However, there was tremendous overlap of anterior commissure size between homosexual and heterosexual men. In addition, many of the subjects died of AIDS and medical information was scanty, a factor which may have affected the results. Moreover, this study requires replication as the only other study that has examined for sex differences in anterior commissure size found the opposite result: larger in men than women[34].

The claim that homosexuality is a biologically predetermined charac-teristic, and homosexuals are "born that way" stands on flimsy genetic, hormonal and neuroanatomic evidence. A consistent and reproducible biologic difference has yet to be demonstrated.

The answer as to the cause of such behaviour and why it appears to be flourishing in today's society is complex, and deserves a separate paper. Briefly, it appears to be the result of many interacting societal and cultural attitudes and influences. Heterosexuality is the basis for the nuclear family, but the nuclear family, particularly in the West is disintegrating. Half of marriages end up in divorce and probably half the children no longer grow up in a stable nuclear family. With the conventional family battered away from many directions, the conventional pattern of sexual behaviour it required is also battered away. Children and adolescents, growing up without any guidance are increasingly engaging in sexual experimentation with their own sex (up to a quarter of all adolescents in some countries, according to some studies). Habits and attitudes developed early in life may affect behaviour in adult life. Exposure to pornography at young ages and other unusual sexual experiences such as molestation by an older individual is also thought to play a role. A vicious circle affect is also created: a visible and vocal homosexual sub-culture appeals to youth (and older adults) looking for adventure and who are increasingly rebellious and take pride in shocking others. These social factors are a more plausible explanation than biologic theories and "born that way" explanations.


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