Last updated on: 3/22/2013 | Author:

Theories on the Origin of Sexual Orientation, 1864-present

A brief synopsis of some major theories on the origin of sexual orientation. Positions are listed as Pro, Con, or Not Clearly Pro or Con (NC) to our core question, “Is sexual orientation determined at birth?” 


1. Third sex theory (Uranism) Karl Heinrich Ulrichs 1864-1879 Pro
2. Bisexual embryo Magnus Hirschfeld 1896 Pro
3. Constitutional bisexuality/theory of immaturity Sigmund Freud 1905/1909 Con
4. In-womb hormonal secretions Eugen Steinach 1917 Con
5. Anima and animus Carl G. Jung 1934 NC
6. Phobic response Sandor Rado 1940 Con
7. Normal behavior Evelyn Hooker, PhD 1957 Pro
8. Parental relationships Irving Bieber, MD 1962 Con
9. Biologically derived Frederick Whitam, PhD 1978 Pro
10. Inclusive fitness Edward O. Wilson, PhD 1978 Pro
11. Structural brain differences Simon LeVay, PhD 1991 Pro
12. Virus or bacteria Paul Ewald, PhD 1999 Con
13. Complex traits, multiple causes Dean H. Hamer, PhD 1999 NC
14. Uncertain and complex George Rice, PhD 1999 NC
15. Multiple causes Daryl J. Bem, PhD 2000 NC
16. Familial and cultural factors Joseph Nicolosi, PhD 2002 Con
17. Developmental problem Traditional Values Coalition 2002-2003 Con
18. Intrauterine hormonal events Vernon L. Quinsey, PhD 2003 Pro
19. Transaction between nature and nurture Matt Ridley, PhD 2003 NC
20. Environmental, cognitive and biological factors American Psychological Association 2004 NC
21. Genes passed down by female maternal relatives Andrea S. Camperio Ciani, PhD 2012 Pro


Theorist Theory / Synopsis Pro, Con, or NC
1. Karl Heinrich Ulrichs Theory: Third sex theory (Uranism)   

1864-1879 — The German lawyer Karl-Heinrich Ulrichs publishes a series of pamphlets in which he declares ‘man-male love’ to be inborn. Supposedly it is the natural, healthy expression of a ‘female soul in a male body’ – a condition he calls ‘Uranism’. Those characterized by this condition he calls ‘Uranians’.

By means of this hypothesis, Ulrichs hopes to demonstrate the injustice of punishing sexual contact between men: Uranians do what they do because of what they are. No legislator, however, should punish people for what they are. Above all, Ulrichs wants to prevent the extension of the unreformed Prussian law against ‘unnatural vice’ to all German states.”

2005 Archive for Sexology (formerly known as Magnus Hirschfeld Archive for Sexology)

2. Magnus Hirschfeld Theory: Bisexual embryo   

1896 — Published in a German pamphlet, “Sappho and Socrates,” which describes the origin of homosexuality as taking place in a bisexual embryo.

“Hirschfeld posited the existence, in the embryos of both sexes, of rudimentary neural centers for attraction to both males and females. In most male fetuses, the center for attraction to women developed, while the center for attraction to males regressed, and vice versa for female fetuses. In fetuses destined to become homosexual, on the other hand, the opposite developmental sequence took place.

While admitting that the location of these centers was still unknown, Hirschfeld predicted that when they were identified, it would be found that adults of each sex carried the vestigial remnants of the centers typical for the other sex.

In keeping with the then current ideas about “degeneracy” (Entartung), he suggested that the cause might lie with a weakening of the parents’ seed on account of alcoholism, syphilis, and so forth. Perhaps recalling that his own parents had led exemplary lives, he added rather lamely that homosexuals could also crop up in apparently healthy families.”

1903 — Published book Der Urnische Mensch (“The Homosexual”) — “Hirschfeld did not think that there was a single male-female continuum, along which any individual could be assigned a unique position. Rather, he held that there are a number of sex-related traits, including gonadal anatomy, genital anatomy, anatomy of other parts of the body, personality, and sexual orientation, any one of which could be used to describe an individual as being more male-like or more female-like. Thus sex was multidimensional, and ‘male’ and ‘female’ were abstractions.

Hirschfeld now believed that same-sex orientation was sometimes accompanied by physical characteristics of the opposite sex: the hips of some gay men were broader than average, for example, while those of some lesbians were sometimes narrower. Similarly, facial appearance might be typical of the other sex, making it relatively easy for the individual to pass as the other sex if he or she so desired.

Later in his career, Hirschfeld even speculated that some gays and lesbians were intersexed in terms of their reproductive physiology: he suggested that it would be worthwhile to examine the vaginal secretions of lesbians for the presence of spermatozoa, and the urine of gay men for menstrual blood.”

1996 Simon LeVay

3. Sigmund Freud Theory: Constitutional bisexuality/theory of immaturity   

1905/1909 — “In 1905’s Three Essays on the Theory of Sexuality, he put forward sexual theories, including his thoughts on the origins and meanings of homosexuality.

Freud believed that homosexuality could be the natural outcome of normal development in some people. He noted that homosexuality could occur in individuals who had no other signs of deviation and no impairment in their functioning. However, he did not view homosexuality, or inversion as he called it, as a sign of illness, by which he meant a symptom arising from psychic conflict. Instead, he saw homosexuality as the unconflicted expression of an innate instinct.

Freud believed in a constitutional bisexuality; that in every individual there was a certain component of masculine (active) as well as feminine (passive) tendencies. Although bisexual tendencies were universal, Freud believed some people were constitutionally endowed with more of one tendency than the other. He believed life experiences, particularly traumatic ones (environmental factors), could have an impact on the development and expression of one’s innate instincts (biological factors). Under normal and non-traumatic circumstances, the component instincts that determine the sex of one’s final object choice should be consistent with one’s anatomical sex. That is to say an anatomic male should ideally express the masculine component instinct and obtain sexual satisfaction from women. However, Freud also believed that even adult heterosexuals retain the homosexual component, albeit in sublimated form.

Freud saw adult homosexuality as a developmental arrest of childhood instincts which prevent the development of a more mature heterosexuality, referred to as Freud’s Theory of Immaturity.”

1996 Simon LeVay

4. Eugen Steinach Theory: In-womb hormonal secretions   

1917 — Published in Jahrbuch fur sextuelle Zwischenstufen (“Yearbook of Sexual Intermediaries”). “Steinach performed transplantations of testes and ovaries in rats and guinea pigs. His research showed that these glands secrete hormones into the bloodstream that influence not only the animals’ physical development but also their sexual behavior. These secretions, he argued, were responsible for the “sexualization” of the brain as male or female. He suggested that this sexualization occurs early in life, because the most dramatic effects were seen when the transplantations were performed shortly after birth.

Steinach developed the notion, partly under the influence of Hirschfeld’s biological theories, that the testicular secretions in homosexual men were abnormal and that they drove brain development in a female rather than a male direction. He even claimed to see microscopic differences in the structure of the testis between homosexual and heterosexual men; these differences were not in the sperm-forming cells but in the ‘interstitial’ cells, the cells that he had shown to be responsible for the secretion of testicular hormones.

In 1917 he published a sensational report in the Jahrbuch that described the results of transplanting a testicle from a heterosexual man into an ‘effeminate, passive homosexual man.’ According to the report, the man was totally ‘cured’ — he was said to have lost all attraction to men and to have developed normal heterosexual feelings.

Some further successes were reported, but eventually the procedure was exposed as ineffective.”

1996 Simon LeVay

5. Carl G. Jung Theory: Anima and animus (born with male & female traits, sexual orientation influenced by parents)   

1934 — Theorized that “every man carries within him the eternal image of woman, not the image of this or that particular woman, but a definitive feminine image. This image is fundamentally unconscious, an hereditary factor of primordial origin engraved in the living organic system of the man, an imprint or ‘archetype’ of all the ancestral experiences of the female, a deposit as it were, of all the impressions ever made by woman … Since this image is unconscious, it is always unconsciously projected upon the person of the beloved, and is one of the chief reasons for passionate attraction or aversion.” (The Development of Personality, 1934)

“The more rational the polity, the more blurred is the difference between the sexes. The role homosexuality plays in modern society is enormous. It is partly the consequence of the mother-complex, partly a purposive phenomenon (prevention of reproduction).”

1961 Memories, Dreams, Reflections Carl G. Jung, MD

6. Sandor Rado Theory: Phobic response   

1940 — “Sandor Rado rejected Freud’s assumption of inherent bisexuality, arguing instead that heterosexuality is inborn and that homosexuality is a phobic response to members of the other sex.”

2005 Gregory M. Herek, PhD


7. Evelyn Hooker, PhD Theory: Normal behavior   

1957 – Published “The Adjustment of the Male Overt Homosexual,” (Journal of Projective Techniques, Vol. 21, pp. 18-31), which “challenged the widespread belief that homosexuality is a pathology by demonstrating that experienced clinicians using psychological tests widely believed at the time to be appropriate could not identify the nonclinical homosexual group. This revolutionary study provided empirical evidence that normal homosexuals existed, and supported the radical idea then emerging that homosexuality is within the normal range of human behavior.”

1991 American Psychological Association


8. Irving Bieber, MD
Theory: Parental relationships   

1962 – “Irving Bieber studied 106 male homosexual patients who were being treated by him or other psychiatrists and found that early cross-gender behavior, including patterns that are thought of as feminine, was the most common element in their background. He thus realized that the phenomenon that became homosexuality among adults actually started very early, long before the hormonal surge at puberty focused the attention of the young man on sex. However, Bieber was also the source of another idea that seems to be an oversimplification or an error in interpretation: he attributed this early behavior to parental patterns that emphasized a strong binding relationship with mothers and weak or absent fathers.”

1993 Vern Bullough, PhD, F.A.A.N, R.N.

9. Frederick Whitam, PhD Theory: Biologically derived   

1978 — He noted that “Although all people in all societies with rare exceptions are socialized to be heterosexual, the predictable, universal appearance of homosexual persons, despite socialization into heterosexual patterns of behavior suggest not only that homosexual orientation is biologically based but that sexual orientation itself is also biologically derived.”

1993 Vern Bullough, PhD, F.A.A.N, R.N.

10. Edward O. Wilson, PhD Theory: Inclusive fitness   

1978 — “He hypothesized a possible genetic predisposition for homosexuality in certain humans by using a theory he calls ‘inclusive fitness,’ defined as the sum of the individual’s reproductive successes plus the reproductive success of others who carry that person’s genes. He explained that there are homosexual genes that exist not only in the individual who is homosexual but in his relatives. Homosexual persons contributed to the survival of the family by not having children so they were available to support and help other family members, by serving in roles such as aunt, uncle, shaman, or medicine man. Thus, genes for homosexual orientation increased in frequency, not because they aided the homosexual person in his or her own survival but because they aided the relatives who shared his gene pool. This broader spread of the genes helps explain how persons with the homosexual genes could be reproduced, since they themselves often did not produce offspring.”

1993 Vern Bullough, PhD, F.A.A.N, R.N.


11. Simon LeVay, PhD Theory: Structural brain differences   

1991 — Stated in the article “A Difference in Hypothalamic Structure Between Heterosexual and Homosexual Men,” published in the Aug. 30, 1991 issue of Science: “The discovery that a nucleus differs in size between heterosexual and homosexual men illustrates that sexual orientation in humans is amenable to study at the biological level, and this discovery opens the door to studies of neurotransmitters or receptors that might be involved in regulating this aspect of personality. Further interpretation of the results of this study must be considered speculative.”

1991 Simon LeVay, PhD


12. Paul Ewald, PhD Theory: Virus or bacteria   

1999 — Evolutionary microbiologists and epidemiologists, most notably University of Louisville biologist Paul Ewald, have been working on a theory that many supposedly noninfectious chronic diseases may actually have an infectious origin. Mental illnesses of several types may have infectious origin. Streptococcus infection could cause obsessive compulsive disorder, either directly or due to a stimulated immune response. Schizophrenia may be caused by Borna virus or a relative. Depression is too common to be of genetic origin, Ewald thinks, and could have an infectious cause. He thinks that even homosexuality may have an infectious origin, since it appears to work against species fitness and theoretically would not persist if it were of genetic origin.

1999 Atlantic Monthly


13. Dean H. Hamer, PhD Theory: Complex traits, multiple causes   

1999 — Stated in an August 6 article in journal Science (Vol. 285, p. 803a) — “Sexual orientation is a complex trait that is probably shaped by many different factors, including multiple genes, biological, environmental, and sociocultural influences.”

1999 Dean Hamer, PhD


14. George Rice, PhD Theory: Uncertain and complex   

1999 — Stated in an August 6 article in journal Science (Vol. 285, p. 803a) — “The basis of sexual orientation remains uncertain, but the pathways involved can be expected to be complex. The controversies and methodological difficulties notwithstanding, the study of sexual orientation contains fascinating riddles, and further careful systematic study has the potential to reveal important insights about who we are.”

1999 George Rice, PhD

15. Daryl J. Bem, PhD Theory: Multiple causes   

2000 – An Augst 6 article in the journal Archives of Sexual Behavior (Vol. 29, Issue 6, Page 531+) stated “[B]iological variables such as genes or prenatal hormones do not code for sexual orientation per se but for childhood temperaments, such as aggression and activity levels. A child’s temperaments predispose him or her to enjoy some activities more than other activities…. Children who prefer sex-typical activities and same-sex playmates are referred to as gender conforming; children who prefer sex-atypical activities and opposite-sex playmates are referred to as gender nonconforming.

[T]o the extent biological factors such as the genotype, prenatal hormones, or brain neuroanatomy influence an individual’s later sexual orientation, they do so only indirectly, by intervening earlier in the chain of events to influence a child’s preference for sex-typical or sex-atypical activity and peer preferences — his or her gender conformity or nonconformity.”

2000 Daryl J. Bem, PhD

16. Joseph Nicolosi, PhD Theory: Familial and cultural factors   

2002 — States on his website “Homosexuality is almost certainly due to multiple factors and cannot be reduced soley to a faulty father-son relationship. Fathers of homosexual sons are usually also fathers of heterosexual sons — so the personality of the father is clearly not the sole cause of homosexuality. Other factors I have seen in the development of homosexuality include a hostile, feared older brother; a mother who is a very warm and attractive personality and proves more appealing to the boy than an emotionally removed father; a mother who is actively disdainful of masculinity; childhood seduction by another male; peer labeling of the boy due to poor athletic ability or timidity; in recent years, cultural factors encouraging a confused and uncertain youngster into an embracing gay community; and in the boy himself, a particularly sensitive, relatively fragile, often passive disposition.”

2002 Joseph Nicolosi, PhD

17. Traditional Values Coalition (TVC) Theory: Developmental problem   

2002-2003 — States on their website “…the most credible research to date on homosexuality — and research conducted years ago — demonstrates that no one is ‘born gay.’ The homosexual is suffering from a developmental problem, which frequently starts out in childhood as gender confusion, family dysfunction, or molestation.”

2002-2003 Traditional Values Coalition

18. Vernon L. Quinsey, PhD Theory: Intrauterine hormonal events   

2003 — stated in an article in journal Annals of the New York Academy of Sciences (Vol. 989, pp. 105-117) “People discover rather than choose their sexual interests. The process of discovery typically begins before the onset of puberty and is associated with an increase in the secretion of sex hormones from the adrenal glands. However, the determinants of the direction of sexual interest, in the sense of preferences for the same or opposite sex, are earlier. These preferences, although not manifest until much later in development, appear to be caused by the neural organizational effects of intrauterine hormonal events. Variations in these hormonal events likely have several causes and two of these appear to have been identified for males. One cause is genetic and the other involves the sensitization of the maternal immune system to some aspect of the male fetus. It is presently unclear how these two causes relate to each other. The most important question for future research is whether preferences for particular-aged partners and parts of the male courtship sequence share causes similar to those of erotic gender orientation.”

2003 Vernon L. Quinsey, PhD

19. Matt Ridley, PhD Theory: Transaction between nature and nurture   

2003 — Stated in his book Nature v. Nurture; Genes, Experience, & What Makes Us Human (HarperCollins Publishers, Inc., 2003) “Nature versus nurture has been declared everything from dead and finished to futile and wrong — a false dichotomy. Everybody with an ounce of common sense knows that human beings are a product of a transaction between the two….I believe human behavior has to be explained by both nature and nurture.”

2003 Matt Ridley, PhD

20. American Psychological Association Theory: Environmental, cognitive and biological factors   

2004 — States on their website: “There are numerous theories about the origins of a person’s sexual orientation; most scientists today agree that sexual orientation is most likely the result of a complex interaction of environmental, cognitive and biological factors. In most people, sexual orientation is shaped at an early age. There is also considerable recent evidence to suggest that biology, including genetic or inborn hormonal factors, play a significant role in a person’s sexuality. In summary, it is important to recognize that there are probably many reasons for a person’s sexual orientation and the reasons may be different for different people.

Is Sexual Orientation a Choice?

No, human beings can not choose to be either gay or straight. Sexual orientation emerges for most people in early adolescence without any prior sexual experience. Although we can choose whether to act on our feelings, psychologists do not consider sexual orientation to be a conscious choice that can be voluntarily changed.”

2004 American Psychological Association

21. Andrea S. Camperio Ciani, PhD Theory: Genes passed down by female maternal relatives   

2012 — Natalie Wolchover, Staff Writer for the Life’s Little Mysteries website, stated: “…[C]onsidering that the trait [male homosexuality] discourages the type of sex that leads to procreation — that is, sex with women — and would therefore seem to thwart its own chances of being genetically passed on to the next generation, why are there gay men at all?

Put differently, why haven’t gay man genes driven themselves extinct?

This longstanding question is finally being answered by new and ongoing research. For several years, studies led by Andrea Camperio Ciani at the University of Padova in Italy and others have found that mothers and maternal aunts of gay men tend to have significantly more offspring than the maternal relatives of straight men…

The theory holds that the same genetic factors that induce gayness in males also promote fecundity (high reproductive success) in those males’ female maternal relatives. Through this trade-off, the maternal relatives’ ‘gay man genes,’ though they aren’t expressed as such, tend to get passed to future generations in spite of their tendency to make their male inheritors gay…

But how might the ‘gay man gene’ make females more reproductively successful? A new study by Camperio Ciani and his team addresses the question for the first time…

Turns out, the moms and aunts of gay men have an advantage over the moms and aunts of straight men for several reasons: They are more fertile, displaying fewer gynecological disorders or complications during pregnancy; they are more extroverted, as well as funnier, happier and more relaxed; and they have fewer family problems and social anxieties. ‘In other words, compared to the others, [they are] perfect for a male,’ Camperio Ciani said. Attracting and choosing from the best males enables these women to produce more offspring, he noted.”

2012 Natalie Wolchover