Homosexuality: Nature or Nurture
Ryan D. Johnson

April 30, 2003


homoIn recent decades, many hotly debated topics have come under the scrutiny of sociobiologists, trying to determine their causation and origins. One such topic is homosexuality. Originally thought by the American Psychological Association (hereafter referred to as APA) to be a mental disorder, research into its causes, origins, and development have consequently led to its removal by the APA from its list of diagnoses and disorders [1]. Many different theories can be found regarding the root of homosexuality, as far back historically as Ancient Greece. The current debate is whether or not homosexuality is a result of nature: a person’s environment and surroundings, or of his biology and genetics. The debate endures because both sides have the ability to create a scientific environment to support their cause. For example, biological theorists may argue that a monkey and human child, reared in the same setting, will develop with vastly different outcomes, while social theorists may argue that monozygotic twins, one reared normally and the other raised in seclusion for 18 years, will also develop with vastly different results, but different even more from the first scenario [4].

In debating sexual orientation, much is unknown; according to Charles Darwin, “…we do not even in the least know the final cause of sexuality. The whole subject is hidden in darkness.” [2]. Although the APA currently states that sexual orientation is not a choice, rather that “…it emerges from most people in early adolescence with no prior sexual experience”[1], social theorists argue that an individual’s upbringing can directly influence this [sexual orientation]. Also tied in with many of these debates is the morality of homosexuality. But the purpose of this examination is not to prove whether or not homosexuality is right or wrong, but rather to establish a thorough understanding of the biological and social theories surrounding the cause of homosexuality.

Let us first look at the biological debate. Biological theorists have found substantial instances of anatomical, genetic, and endocrine evidence to support their argument. Experiments in biological research date back as far as the late 1930’s, beginning with the pioneering research of Alfred Kinsey (for the University of Indiana) on human sexuality. Kinsey had two goals for his tests: 1) to find out how many adult males engaged in homosexual behavior, and 2) to suggest theories about it came to be [9]. When asked if they had engaged in homosexual sexual relations, a large percent of the population tested answered “no”, however when asked if they had engaged in same-sex sexual relations, the percentage answering “yes” nearly doubled. The experiment yielded that 30% of males had experienced at least orgasm in a homosexual act. The results of this research became the widely popularized Kinsey Scale of Sexuality. This scale rates all individuals on a spectrum of sexuality, ranging from 100% heterosexual to 100% homosexual, and everything in between [7]. While establishing that as many as 10% of adult males reported having sexual relations with a same-sex partner, this research did little more than to put the word homosexual into common language.

Karen Hooker executed the first psychological test done to test for biological determinism in 1957, on a grant from the National Institute of Mental Health [2]. The study was meant to explore the relationship between homosexuality and psychological development and illness. Hooker studied both homosexuals and heterosexuals. Both groups were matched for age, intelligence quotient (IQ) and education level, and were then subjected to three psychological tests. These three tests, the Rorschach, Thematic Apperception Test (TAT) and the Make-A-Picture-Story Test (MAPS), were then analyzed by psychologists, and the results were tabulated. The results of Hooker’s experiment yielded no significant differences in answers on any of the three tests. Because both groups’ answers scored very similarly, she concluded a zero correlation between social determinism of sexuality.

As a result of Hooker’s finding, the APA removed homosexuality from its Diagnostic and Statistical Manual of Psychological Disorders in 1973. In 1975 it then released a public statement that homosexuality was not a mental disorder. In 1994, two decades later, the APA finally stated, “…homosexuality is neither a mental illness nor a moral depravity. It is the way a portion of the population expresses human love and sexuality” [2].

D.F. Swaab conducted the next noteworthy experiment in 1990. This experiment became the first to document a physiological difference in the anatomical structure of a gay man’s brain. Swaab found in his post-mortem examination of homosexual males’ brains that a portion of the hypothalamus of the brain was structurally different than a heterosexual brain. The hypothalamus is the portion of the human brain directly related to sexual drive and function. In the homosexual brains examined, a small portion of the hypothalamus, termed the suprachiasmatic nucleus (SCN), was found to be twice the size of its heterosexual counterpart [2].

At the same time, another scientist, Laura S. Allen made a similar discovery in the hypothalamus as well. She found that the anterior commissure (AC) of the hypothalamus was also significantly larger in the homosexual subjects than that of the heterosexuals [2]. Both Swaab’s and Allen’s results became a standing ground for the biological argument on homosexuality. The very fact that the AC and the SCN are not involved in the regulation of sexual behavior makes it highly unlikely that the size differences results from differences in sexual behavior. Rather the size differences came prenatally during sexual differentiation. The size and shape of the human brain is determined biologically and is impacted minutely, if at all by behavior of any kind.

Simon LeVay conducted another experiment regarding the hypothalamus of the human brain in 1991. LeVay, like Swaab and Allen also did a post-mortem examination on human brains; however, he did his examinations on patients who had died from AIDS-related illnesses. He examined 19 declared homosexual man, with a mean age of 38.2, 16 presumed heterosexual men, with a mean age of 42.8, and 6 presumed heterosexual women, with a mean age of 41.2 [3]. LeVay discovered that within the hypothalamus, the third interstitial notch of the anterior hypothalamus (INAH3) was two to three times smaller in homosexual men then in heterosexual men. The women examined also exhibited this phenomenon. LeVay concluded the “homosexual and heterosexual men differ in the central neuronal mechanisms that control sexual behavior”, and like Allen and Swaab, agreed that this difference in anatomy was no product of upbringing or environment, but rather prenatal cerebral development and structural differentiation [2].

Another line of testing done to support the biological perspective are neuroendocrine studies. The neuroendocrine viewpoint’s basic hypothesis is that sexual orientation is determined by the early levels (probably prenatal) of androgen on relevant neural structures [7]. If highly exposed to these androgens, the fetus will become masculinized, or attracted to females. This research was conducted on rats at Stanford. The adult female rats that received male-typical levels of androgens sufficiently early in development exhibited male symptoms of attraction. The same was true in the reverse when applied to the male subjects. The female exposed to high levels of the hormone exhibited high levels of aggression and sexual drive toward other females, eventually trying to mount the other females in an act of reproduction. In the males, the subject who received deficient levels of androgen became submissive in matters of sexual drive and reproduction and were willing to receive the sexual act of the other male rat [7].

A popular route of experimentation in general psychology also did not elude the biological argument. Twin studies have become a highly debated area of experimentation. Ernest Kallman conducted the earliest twin study. He found a 100% concordance between monozygotic (or identical) twins (MZ), and only a 12% concordance for dizygotic (or fraternal) twins (DZ). Although discredited with methodological problems, the early experiment paved the way for a much-publicized team to conduct their twin studies.

J. Michael Bailey and Richard Pillard also studied the gayness between MZ twins, DZ twins, and non-related adopted brothers. They examined how many of the sample population examined were gay and how many were straight. They found that 52% of MZ twins were both self-identified homosexuals, 22% of DZ twins were so, and only 5% of non-related adopted brothers were so. This evidence, repeated and found to be true a second time, showed to the biological camp that the more closely genetically linked a pair is, the more likely they both are to exhibit gay or straight tendencies. Later experimenters found similar evidence in females. One such scientist is Dean Hamer. Hamer examined the possibility of homosexuality being an X-linked trait. He examined the family trees of openly gay men, and thought he saw a maternal link, leading him to investigate his theory of X-linkage. He took 40 DNA samples from homosexual men, and genetically examined them. He found that there was a ‘remarkable concordance’ for 5 genetic markers on section of the X-Chromosome called Xq28 [2].

Hamer hypothesized upon examining the family trees of the same men that on each subject’s mother’s side, there were markedly larger numbers of homosexual men, all stemming through the maternal lineages. This observation, along with his startling discovery on Xq28, led his findings to be dubbed the “gay gene study”. The statistical probability of the 5 genetic markers on Xq28 to have matched randomly was calculated to be 1/100,000 [2], lending even more support to his findings.

This finding of a possible ‘gay gene’ prompts a look into two evolutionary concepts, and how they are affected. The Superior Heterozygote Theory states the phenotypic (actual) expression of homosexuality is the result of homozygosity for recessive (non-expressed but present) genes [11]. In simplification, if the person’s genetic code is heterozygotic (one homosexual gene and one heterosexual gene), if the homosexual allele (half of the genetic code) is the allele passed on to the next generation, it will become the phenotype. Heterozygotes are only capable of being passed through to the next generation by mothers (as the Y-chromosome is incapable of heterozygosity), this again links homosexuality to X-linkage.

While all of this scientific experimentation and conclusion seems evidentiary, sociobehaviorists are not convinced. This opposing point-of-view proposes that homosexuality is the result of environmental factors, not biological ones. Most social theorists see childhood elements as the largest contributing factors to homosexuality. Often they examine childhood play patterns, early peer interactions and relations, differences in parental behavior toward male and female children, and the role of gender constancy in the household [9].

The social argument for homosexuality dates back to the ancient Greeks. Aristophanes, in his Symposium investigates homosexuality, although not termed as such, as a desire by men to share a long-term fulfillment of the soul. He believed that two souls are longing to be together, and the sexual desire alone is not strong enough to create homosexuality, but that the cultural environment allows or forbids the relationship to occur [10]. In Greece is it well known that many men engaged in same-sex relationships, however, these were not equal relationships, they were older men to young boys going through the transition to adulthood. Two instances where the culture is a causative agent of homosexual expression are in New Guinea and Crete. In some tribes in New Guinea, young boys ages 8-15 are inseminated daily by the young male warriors of the tribe. In Crete, every adolescent boy undertook a homosexual relationship as a rite of passage into manhood [10]. In these two instances, the homosexuality is accepted; however, it can be argued that it is also forced, not a natural expression.

Most psychoanalytic theories, however, stress the role of parental and family dynamics, not the society as a whole. Behaviorists believe that some sexual and gender identification differences result from roles imposed by family and friends upon children, such as the masculine and the feminine stereotypes. Problems with this are there is no evidence, social or biological, to support that homosexual children were raised differently than were the heterosexual children. Also, with reinforcement of gender identification norms, one would be led to logically deduce that all of the stereotype reinforcement would ensure a heterosexual outcome [7].

While it is agreed that an element of gender ID is based on the decision made by parents on how to raise the child, the other element is formed with the development of language skills, naming of sexual behaviors and the naming process related to these behaviors [9]. Gender ID is learned over time, and other contributions include the frequency of parental interactions, tolerance of aggression levels, and the vigor of play during childhood. In this, another theory is acknowledged, the Parental Manipulation Theory. This theory is that one or both parents are able to neuter and control offspring to promote their (the parent’s) evolutionary fitness, ensuring the passage of genes into the next generation. By selecting only heterosexual practices as acceptable, the parents are attempting to promote their passage of genes [5]. However the Kin-Selection Theory contrasts this. This theory states that it doesn’t matter how the genes are passed to the next generation, so long as they are passed along. For example, regardless of a homosexual outcome, the very similar genetic makeup of siblings will still allow for the passage of the family genetics along to the next generation [9].

Two predominant social theorists on homosexuality are David Halperin and Jean Foucault. Although both social theorists, both have largely contrasting ideas on the environmental contributions to the formation of an individual’s homosexuality. Halperin believed in Planophysical theory. This theory believes that homosexuality is a freak of nature, an error. His theory follows in the tradition of psychological theory on this subject. Halperin was a Freudian psychologist, and places stock in Freud’s idea that homosexuality is derived from a failure to resolve Oedipal issues [10]. Although Halperin has a large following from interest groups such as Christian coalitions, his theory is largely disrespected by the psychological community at large, as it provides only a result, not a cause. He fails to produce any scientific evidence. He does, however, provide examples. He postulates that a weak father and strong mother, with an unresolved Oedipus complex will lead to a weak, and then homosexual, son, because the mother has too strong of an image, compared to the weak state of the father. Psychologists argue that this same arrangement would also possibly lead to a stronger son, striving for compensation of his father’s weakness.

Jean Foucault argues, “…homosexuality became because we made it so” [11]. Foucault says that the category of homosexuality itself was only created a mere one hundred years ago, after a German neologism coined some twenty years later. Foucault gives root to the social derivation of homosexuality believing that homosexuality appeared as one of the forms of sexuality, only “after it was transposed from the practice of sodomy into a kind of interior androgyny, a hermaphrodism of the soul” [10]. The theorists believe that the homosexual had been an aberration, and had then become a species, justifying itself with a new word.

Although both theorists represent the major ideas of the socioenviromental belief, there are three differences in the two theories. The first is based on the depth of desire. Foucault believed that the depth of desire is only sexual preference, that it is nothing more than superficial tastes and preferences. Halperin contrasts this with saying that homosexuality does go deeper than superficial tastes, and that homosexuality is a psychological condition, with much deeper roots than mere sexual preference. The second major difference is that Foucault did not divide people into categories. Halperin acknowledged that there are three general categories of people in respect to sexuality: heterosexual, gay men, and lesbians. Foucault groups gay men and lesbians into the all-inclusive term of homosexual. The third difference is that Halperin see homosexuality as a symmetrical and equal relationship, Foucault believes that historically, as far back as the Greeks, before the term was coined, homosexuality has always been unequal, differences in race, age, education and social status influencing the ‘superficial’ tastes and preferences of the men influenced.

We have examined many causes for homosexuality in the preceding pages, both biological and social. And although an interesting topic of debate, no one theory or experiment leads to a definitive answer. Some believe that the characters found on Xq28 are the Holy Grail of homosexuality research, the elusive ‘gay gene’. Others may place stock in the theories of Foucault and Halperin. Perhaps Simon LeVay did reveal to us that anatomy is the key to understanding the difference in sexual orientation. Perhaps there is no one answer, that sexual orientation, whether homosexual or heterosexual; gay, straight, lesbian, or bisexual, all are a cause of a complex interaction between environmental, cognitive, and anatomical factors, shaping the individual at an early age.


[1] APA Online. “Answers to Your Questions About Sexual Orientation and Homosexuality”. Online. 11 April 2003. Available https://www.apa.org/pubinfo/answers.html.

[2] “Biological Basis for Homosexuality.” Online. 8 April 2003. Available


[3] Bull, James J. and Pease, Craig M. “Biological Correlates of Being Gay” Online. 11 April 2003. Available https://www.utexas.edu/courses/bio301d/Topics/Gay/Text.html.

[4] Fujita, Frank. “The Nature-Nurture Controversy.” Online. 8 April 2003. Available https://www.iusb.edu/~ffujita/Documents/nn.html

[5] Hoback, Wyatt. “Lecture 21. Sociality.” Online. 11 April 2003. Available https://www.unk.edu/acad/biology/hoback/2002bio470/470lecture21.htm.

[6] Moberly, Elizabeth R. Homosexuality: A New Christian Ethic. James Clarke and Co.; Cambridge, MA, 1983.

[7] Pillard, Richard. “NPR Letters on the Biological Basis of Homosexuality.” Online. 8 April 2003. Available https://cas.bellarmine.edu/tietjen/RootWeb/ npr_letters_on_the_biological_ba.htm

[8] Sullivan, Andrew. Virtually Normal: an Argument about Homosexuality. Alfred A. Knopf; New York, NY, 1995.

[9] Thompson and Devine. “Homosexuality: Biologically or Environmentally Constructed?” Online. 8 April 2003. Available https://jrscience.wcp.muohio.edu/Research/ HNatureProposalsArticles/Homosexuality.biologicall.html

[10] Thorp, John. “The Social Construction of Homosexuality.” Online. 8 April 2003. Available https://www.fordham.edu/halsall/med/thorp.html

[11] Taylor, Tim. “Current Theories on the Genesis of Homosexuality.” Online. 11 April 2003. Available https://www.dai.ed.ac.uk/homes/timt/ papers/twin_studies/theories.html.