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Biology 202, Spring 2005
Third Web Papers
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Homosexuality: Born or Made?

Kristin Giamanco

Are we born the way we are? Or are we molded and shaped by environmental factors and our upbringing? This nature versus nurture debate has been one that we have discussed extensively in class. In order to resolve some of the questions that I have concerning this matter, I decided to dedicate this paper to analyzing nature versus nurture in terms of homosexuality. This paper will examine both schools of thought, interjecting my own criticism of the evidence and ideas set forth. Furthermore, at the end, I will decide which body of evidence is most valid and attempt to determine if homosexual individuals are born or made.

Some of the earliest studies on homosexuality were performed by Alfred Kinsey of the University of Indiana in the late 1930s. Kinsey wanted to determine how many adult males engaged in same sexual behavior in hopes of understanding why certain individuals were homosexual and while others were straight. Through this survey, he found that 30% of males had experienced at least an orgasm while engaging in a homosexual act. From these results, the Kinsey Scale of Sexuality was born. All individuals were placed on this spectrum ranging from 100% heterosexual to 100% homosexual (1). However, these results hardly seem noteworthy in our present time, because today we know that individuals may exhibit a range of sexual behaviors, but his study helped individuals place themselves on a continuum and define themselves sexually.

Karen Hooker created the first psychological tests in hopes of determining if homosexuality was a socially created characteristic. These tests were conducted in 1957 under a grant from the National Institute of Mental Health (NIMH) and included the Rorschach, Thematic Apperception Test (TAT), and Make-A-Picture-Story Test (MAPS). When psychologists analyzed the results from this battery of examinations, they concluded that there was no correlation between social determinism and homosexuality (1). However, I feel that this test is not necessarily designed to investigate the relationship between social behavior and homosexuality. Personally, I feel that these two groups of individuals most likely will not test differently in terms of perceptions and picture analysis any more than individuals of the same group would test differently. Therefore, how can psychologists control for variation in the heterosexual group and the homosexual groups? Perhaps the individuals who classify themselves as straight were gay, and vice versa. Hence, I believe these tests really do not disprove the nurture debate in any way.

As a result of these executed tests the American Psychological Association (APA) eliminated homosexuality from its Diagnostic and Statistical Manual of Psychological Disorders in 1973. Later in 1975, the APA announced that homosexuality was not a mental disorder and in 1994 they acknowledged that it was neither a mental illness nor a moral depravity (1).

In 1984 a group of researchers at the State University of New York at Stony Brook corroborated a German study which indicated that male homosexuals differ from their heterosexual counterparts as well as heterosexual females in their response to injections of estrogen (which will be further fleshed out later on in the paper) (2). In 1990, D.F. Swaab of the Netherlands Institute for Brain Research found that homosexual men had a larger suprachiasmatic nucleus (SCN) than their counterparts. This structure was found in the hypothalamus, which has been implicated in playing a role in sexual drive and function (1), (2). Laura Allen and Roger Gorski, both scientists of the University of California at Los Angeles (UCLA) School of Medicine, also determined another difference in the brain structure within these two groups of individuals. Brains of the individuals during autopsies were examined in these studies. Allen and Gorski found the differences originated in the anterior commissure (AC) of the hypothalamus. More specifically, they concluded that the AC was 34% larger in homosexual males than heterosexual males (3). The SCN and AC do not have a direct role in sexual drive and function. Moreover, the SCN is responsible for the establishment of circadian rhythms and regulates the body over the 24-hour day (4), while the AC is the structure which divides the left and right halves of the brain and is located in the back of the skull (3), (4). Therefore, it would be improbable that these differences arose due to sexual practices. Rather, researchers concluded that these differences were innate (1). As a budding biologist and researcher, this theory seems extremely plausible to me. These differences in brain structure would not have arisen due to sexual practice, instead it seems that these differences were present already and then affected individuals in terms of their sexuality.

The results obtained which determined the differences in the AC region for homosexual and heterosexual men were also found by another research group. These scientists published their results in the Proceedings of the National Academy of Sciences of the United States of America (PNAS) and also reported a larger AC structure in women and homosexual men as compared to heterosexual men. The sample population included 34 homosexual men, 75 heterosexual men, and 84 heterosexual women (3). However, these results may not be as valid because the individuals under study were mostly men who died from AIDS. Since the investigators did not take this variable into consideration when making their claims, this may detract from their results.

One of the landmark studies performed on autopsied brains was done by Simon LeVay, a neurobiologist for the Salk Institute for Biological Studies in San Diego in 1991. His test involved the examination of 41 brains where 19 were self-declared homosexual men (with a mean age of 38.2), 16 presumed heterosexual men (with a mean age of 42.8), and 6 were presumed heterosexual women (with a mean age of 41.2). LeVay discovered that on average, a cluster of cells within the hypothalamus was half as large in the brains of the homosexual men in comparison to heterosexual men. This conglomeration of cells was identified as the interstitial nuclei of the anterior hypothalamus 3 (INAH3). As stated above, the hypothalamus is the center which directs emotions and sexual drives. Therefore, LeVay believed that this difference in the hypothalamus structure was critical in distinguishing these two disparate groups of individuals, thereby providing ample support for the nature component to this hotly contested topic (2). However, what LeVay failed to account for in his analyses diminished his presented results. LeVay’s tests were performed on individuals who died of AIDS-related illnesses. Perhaps the noted structural changes were induced as a result of the illnesses incurred by the individuals (1). While LeVay’s results seemed promising and exciting, before fully accepting his theories the aforementioned bias must be taken into account.

Research has also been done on other organisms, such as sheep. On November 5, 2002, British Broadcasting News (BBC) reported that American researchers found that the preoptic hypothalamus was twice as large in male sheep and male humans in comparison to the females. The cluster of cells was identified to be the sexually dimorphic nucleus. Furthermore, these structures also contained twice the number of cells in the male animals. It was also found that between 6 and 10% of rams were attracted to males rather than females and in these animals the bundle of neurons encapsulated in the sexually dimorphic nucleus was smaller in ewes and rams with the same sex preferences. With this information, scientists hope to parlay these findings into studies done on humans (5). This study provided firm evidence that there is a biological component to sexuality in sheep and perhaps, other more sexually complex systems, such as humans. In the future, it would be interesting to determine if these results were found in humans.

Neuroendocrine studies have also been carried out which involves exploring the affect of hormone levels on the neuronal development. In studies done with rats, it was found that the brain is basically female all through development unless the animal is exposed to certain levels of hormones. These hormones can then cause certain structures in the male brain to grow up to 500% larger than those in the female rat brain (3). This phenomenon has been extensively studied in rats at Stanford University as well. Researchers there concluded that sexual orientation is determined primarily by early levels, most likely, prenatal of androgen on neural structures (1). Androgens were first discovered in 1936 and are steroid hormones responsible for the stimulation and development of masculine characteristics in vertebrates. The most well-known androgen is testosterone. As a family, these steroid hormones are accountable for the development of accessory male sex organs as well as secondary male characteristics (4). Therefore, if rats are highly exposed to such hormones, then they will become males and if newly developing rats are exposed to low levels of androgens, they will be born females. Researchers also found that if female rats are exposed to high levels of these hormones, they exhibited high levels of aggression as well as increased sexual drive toward other females, mimicking the behavior of male rats. Similarly, if male rates were exposed to deficient levels of these hormones, they were found to be sexually submissive and engaged in activities with other male rats (1). Therefore, these results, in conjunction with the aforementioned studies on the brain structures, indicate to me that during development our sexual preferences are established. If this is so, it does not make sense that someone can be raised to be homosexual or heterosexual; instead, we are packaged in such a way that these characteristics are inherent. If we were raised to be straight or gay, then I would expect hormone levels to be uniform in all individuals and then as the individual grows into an adult, these levels should change, however, this is not the case.

In accordance with the aforementioned neuroendocrine studies, researchers in the United Kingdom, the United States of America, and Germany have confirmed that prenatal exposure to low levels of testosterone increases the probability of a man becoming homosexual (3). To me, these data seem a bit simplistic and the notion that it represents just a probability further detracts from the results. Also, if a woman is exposed to low levels of estrogen and high levels of testosterone, will she be more likely to become a lesbian? I found it quite intriguing that most of the research published on homosexuality has been on heterosexual women, frequently neglecting homosexual women. This topic interests me, I wonder if similar results would be noted if female subjects were studied as well. Do researchers think that if they find evidence on homosexual men, then the results should be similar for homosexual women? That does not seem to be the case, at least in my mind. Therefore, I think further research should be done on female organisms.

In 1987 Lindesay, another scientist studied the 94 homosexual men and 100 heterosexual men. Through this study, it was found that 14% of the homosexual men were left-handed in comparison to 9% of the heterosexual men (3). Of all the experiments and results that I researched for this paper, I think this finding is the most coincidental. Statistically speaking, these results do not seem significantly different. Perhaps the population pool they used in this experiment happened to have a large number of left-handed individuals. I find it hard to believe that what hand a person writes with has any bearing on their sexuality. Nonetheless, this result has been reported elsewhere by Sandra F. Witelson of McMaster University in Hamilton, Ontario. Witelson was interested in looking at handedness in terms of development and in her study, she examined homosexual women. Through her investigations, she found that lesbians had a higher incidence of left-handedness as well as in gay men (2). Therefore, this seems to be more than a trend, since the researchers were studying different pools of individuals. However, I do not think this can really be an indicator of one’s sexual preferences.

Dr. Kenneth Zucker of the University of Toronto’s Center for Addiction and Mental Health (CAMH) provided empirical evidence on this topic. Over the span of 50 years, Zucker found that lesbians have a 91% greater chance of being left-handed or ambidextrous than their heterosexual counterparts (6). Therefore, it seems that handedness cannot be used as an indicator; rather these data highlight another set of differences between gay and straight individuals. The reasons for the difference in handedness and its role in sexual preference have yet to be determined, thereby, this area represents another potential research topic.

Another interesting study I found while researching concerned body development in homosexual men and their counterparts. The gay individuals had less subcutaneous fat and smaller muscle and bone development. Their bones are longer in comparison to their bulk as well as the fact they had narrower shoulders in relation to pelvic width. Moreover, there was a noted diminishment of muscle strength in the homosexual men. Creatine and 17-ketogenic steroid levels were lower in these individuals (3), where creatine (creatine monohydrate) is a naturally occurring amino acid which serves to supply energy to muscle cells (4). Researchers also noticed a lower androsterone-etiocholanolone ratio in homosexual men (3). Androsterone is an androgen and is a male sex hormone produced in the testes and is responsible for the development of secondary sex characteristics. Etiocholanolone is a metabolite of testosterone and androstenedione, both hormones produced in mammalian species (7). There were also elevated levels of 11-keto-etiocholanolone in gay men. What I found particularly intriguing was the fact that homosexual men had lower levels of triglycerides, phospholipids, cholesterol, and beta-lipoproteins (3). Are these occurrences happening due to environmental or lifestyle factors? While these data might indicate that homosexuals are born differently, one cannot ignore the idea that over time these findings might be attributed to lifestyle choices or environmental factors. Therefore, I feel that these results and research in and of themselves cannot be used to solely to confirm that homosexuals are born rather than made.

However, there has been more convincing data obtained from identical and fraternal twin studies. Fraternal twins carried in the same womb and reared in the same household have a one-in-four chance of being gay, while identical twins have a one-in-two chance of being gay. For example, if one identical twin is gay, the chance that his brother will be gay is 50% (3). These facts indicated to researchers that perhaps there was a “gay gene.” Both fraternal and identical twins were raised in the same household, but each set of twins had a different probability in becoming gay, which then demonstrated to researchers that nurture is not the primary factor at play here.

J. Michael Bailey and Richard Pillard furthered the aforementioned results on twins, by examining monozygotic twins (identical), dizygotic twins (fraternal), as well as non-related adopted brothers. It was found that 52% of monozygotic twins both identified themselves as homosexuals, while 22% of dizygotic twins did so, and lastly, 5% of non-related adopted brothers both classified themselves as gay (1). Therefore, I feel these results do not solidly support the nature or the nurture theory. In the future, researchers might opt to investigate identical twins that were separated at birth and determine the percentage of both brothers and sisters that were gay. This long term study will enhance the understanding of whether the nature versus nurture theory is applicable.

Scientist Dean Hamer postulated that there was a homosexuality gene and it was inherited as an X-linked trait. He examined family trees and noticed a maternal link and then decided to collect 40 DNA samples from self-proclaimed homosexual men. Through this genetic analysis, Hamer determined that there was a remarkable agreement for 5 genetic markers located on the section of the X-chromosome called Xq-28. This study was then dubbed the “gay gene study.” Hamer then decided to supply empirical data by analyzing the statistical probability that the 5 genetic markers would be present on this portion of the X-chromosome randomly. This value was found to be 1/100,000 (1). Therefore, these quantitative data firmly supports Hamer’s data and hypothesis that there exists a gay gene. Further research should be done on a wider scale in order to determine if this region actually represents an area for the gay gene to be present. These genetic analyses will lend credence to Hamer’s results and this advancement will strongly confirm the idea that individuals are born as gay rather than developing as gay.

I was next interested in looking at the diametrically opposed argument stating that individuals develop to become homosexuals as a result of environmental factors or upbringing. Same-sex relationships in males have been noticed as early as in ancient Greece where Aristophane, believed that men were homosexual in order to seek soul fulfillment. In New Guinea boys ages 8-15 were frequently on the receiving end of sexual relations with young male warriors. Every adolescent boy in Crete partook in a sexual relationship with a man as a rite of passage (1).

Many of the psychological studies analyze parental and familial dynamics such as stereotypes imposed on male and female children. However, there is little biological evidence to support the idea that homosexual and heterosexual children are raised differently and until this investigation can be confirmed through more solid analyses, these results are not entirely reliable. Also, if these gender stereotypes were enforced, then would one think that all children would be heterosexuals (1). For example, if a family instills in their daughter that she should like to play with dolls and play house, while they encourage their son to play with cars and trucks, one would then think that these children would develop most likely as heterosexuals. However, this is not proven to be true, as many boys and girls develop into homosexuals even if they are encouraged by their parents not to do so through the forcing of gender stereotypes.

Within the realm of psychology there exists the Parental Manipulation Theory, which states that one or both parents of a child work to control their offspring in order to promote their (the parental) evolutionary fitness. This control allows for genes to be passed onto the next generation, ensuring the survival of the parental genes. Psychologists believe that in this theory parents pressure their children to engage in heterosexual behavior to facilitate the passage of their genes into the next generation. However, the Kin-Selection Theory states that it does not matter how the genes are passed down into the next generation, as long as they are in some form (1). If a child engages in homosexual relations though, the only way they will be able to have a baby, would be to adopt, therefore, the original parental genes would not be passed down then. It seems to me then that the Parental Manipulation Theory would be the most likely scenario for parents to adopt if they are concerned with the transmission of their genes.

Scientists have also pointed out that the brain changes with use over time. For example, as parts of the brain are used, cell death may be induced as well as the establishment of new connections between cells. The thickness of the connections between the cells can be altered as well as the pruning, or the loss of interneuronal connections. Therefore, some scientists and psychologists argue that as an individual grows and develops their particular sexual preferences, certain areas of the brain may change as a result of either heterosexual or homosexual behaviors (8). However, I do not believe that neuronal connections and cell death is really affected by whether someone engages in a particular relation with another individual. Rather, the changes enumerated above, most likely occur due to trauma, injury, or overall brain development, not sexual activities. Thus, while these scientists and psychologists have tried to argue that being homosexual or heterosexual alters the brain organization, I firmly believe that these changes were not induced by one’s sexuality.

Two social theorists who have discussed homosexuality at length, include David Halperin and Jean Foucault. Halperin believed in the Planophysical theory that homosexuality was a freak of nature, an error. Furthermore, Halperin derived his ideas concerning same-sex behavior from Freud’s analysis of the Oedipus complex. Thus, Halperin believed that men engaged in sexual relations with other men due to a failure in resolving oedipal issues. In the same vein, he concluded that a weak father and a strong mother contributed to men becoming homosexual (1). However, there is no scientific evidence to support this notion and even if there were, there are so many exceptions, that it almost seems like an antiquated theory, Halperin also believed that homosexuality was a psychological condition and he divided individuals into three categories: heterosexual men and women, gay men, and lesbians. Lastly, he believed that homosexuality was a symmetrical and equal relationship between two men, or between two women (1).

Another theorist Jean Foucault came to different conclusions concerning homosexual behaviors. He believed that homosexuality was only created about 100 years ago and that there were only two distinctions: homosexual men and women, and heterosexual men and women. This theorist also thought that homosexuality was only about sexual preference and was not a psychological condition as set forth by Halperin. Foucault concluded that homosexuality was always unequal because there was always a difference between race, age, and educational background (1).

Through examination of the neurobiological evidence as well as the psychoanalytical evidence, I have tried to determine if homosexual individuals are born or if they are made. Therefore, I have addressed the nature versus nurture debate that we have spent many class discussions as well as many forum postings talking about. Many of the psychological studies and theories seem outdated to me and do not provide any persuasive empirical evidence for me to examine, therefore, I am more inclined to believe the nature argument. Based upon the fact that there is such a gross differential brain organization in homosexual versus heterosexual individuals, this seems to be the most valid and plausible explanation. Brain usage could not have altered these structures that much; instead it seems more likely that the individuals were born this way. Furthermore, many of the psychological analyses were unsubstantiated, providing little or no quantitative data. Instead, these studies presented weak theories and links between homosexuality and upbringing.

It seems appropriate to end this semester with a topic that focuses on one of the fundamental questions raised in the first week of classes: Are we born or made into the individuals we are today? Within this realm, I opted to investigate homosexuality and nature versus nurture, and in doing so, I studied both schools of thought in-depth, providing evidence on both sides while assuming a critical role in hopes of determining which theory was most valid. From these examinations, I firmly conclude this paper as well as from my semester in Neurobiology and Behavior that individuals are born homosexual rather than raised. While I am not neglecting environmental factors or upbringing, I feel the main influence must stem from the biological and brain component.


1)AllPsych, a website that discussed Homosexuality: Nature or Nurture, as published in the AllPsych Journal Online.

2)Science News, discussed Gay brains " brain feature linked to sexual orientation as appeared in Science News, August 31, 1991, Vol. 140, No. 9, p. 140.

3)Gay Men’s Brains Found Different , an article which provided insight into the neural differences between homosexual and heterosexual men.

4)Wikipedia, a site used to find definitions and information on various hormones, steroids, and other compounds.

5)BBC News, an article from the BBC News November 5, 2002 discussing research performed on sheep.

6)Sexuality At Hand: Research Links Homosexuality to Left-Handedness, an article that discussed sexuality and handedness.

7)Etiocholanolene, a site used to determine what etiocholanolene did in the body and how it was produced.

8)Biological Research on Homosexuality, a discussion of biological research on homosexuality.

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