The Genetic Basis of Homosexuality


Department of Educational Foundations and Inquiry
Bowling Green State University
Bowling Green, Ohio 43403


JASA September 1981: 153-157

In the past, a common explanation for the origin of homosexuality was the assumption that it was a result of a biological malfunction, either due to improper hormonal levels, or to an inheritance of factors influential toward sexual development. The research on various hypotheses relative to various biological and genetic causes of homosexuality are examined. It is concluded that there is no clear evidence for a biological or genetic basis for homosexuality. In essence, it is a learned behavior; the most supported theories are those which are basically sociological in nature.

One of the stronger arguments for permitting homosexuals to "practice their lifestyle" is the argument that homosexuality is genetically inherited and therefore "cannot be helped any more than color blindness, skin color or any other inherited trait."1 As was stated in Newsweek:2

If homosexuals have little choice in their sexual preference-if homosexuality is no more a matter of choice than being black or female-then they seem entitled to be free of discrimination.

Writings by homosexuals commonly utilize the above argument to justify their sexual orientation. A good example of this is the following quote from Troy Perry's autobiography:3

Now I know that I'm opening Pandora's box when I tell you that I'm sure that homosexuality is preordained ... I am firmly convinced that much of what we are comes to us through our genes. I know that many people will throw up their hands in horror and say: "Why, where could you get such an idea?" Well, I'll just draw a blank. I just believe it, that's all. . I read about a professor. . who is conducting experiments along that very line. The rest of the people can wait for him. But not me. I'm sure. I'm going to go right on and believe it...

If you follow the law of averages, those who catch the brass ring turn out to be homosexuals. Well, I caught the brass ring. And, I'm sure that homosexuality was in my genes, and in my soul, from the very beginning.

Simms, 4 from his review of the literature, concluded that, "some clinicians and therapists claim that some homosexual persons may be constitutional [born homosexuals], and perhaps the majority of practicing homosexuals insist that this is so."

Beliefs Common During the Early 1900's

The belief that homosexuality was inherited was held by many scientists until recently.5 It was commonly believed that a homosexual was a man born with a woman's disposition and a man's body and was actually "a third sex," which was an aberration of nature. Even today, homosexuals are called "the third sex."6

In 1896, the well-known German psychologist, Krafft-Ebing,7 suggested that homosexuality was an inborn characteristic caused by large amounts of male and/or female substances in the hereditary composition of the brain, Havelock Ellis,8 who uncritically accepted Krafft-Ebing's conclusions, caused the notion that homosexuality was of a biological origin to become commonly accepted. Mantegazza9 explained homosexuality as a genital malformation caused by the displacement of sensory nerves which normally originate in the penis, but which in homosexuals have, in essence, shifted to the rectum. The erogenous zone, he felt, had shifted correspondingly. Later, Hirschfeld10 concluded that "homosexuality is always an inborn state, conditioned by specific homosexual constitution of the brain." Glass and other researchers felt that hormonal or endocrine factors were influential.

The Public's Attitudes

Before we review the genetic evidence, we briefly look at the public's attitudes regarding the innate/learned controversy. A 1977 Gallup Poll12 relates: "The great majority of Americans are convinced that homosexuality is more prevalent today than 25 years ago . . . At the same time a majority of the public, 56% believes homosexuality to be a product of upbringing and social environment rather than innate predisposition-a view only 12% hold. Another 14% say both factors are involved." Interestingly, the less education a person has, the more likely he is to believe that homosexuality is innate. Of the college graduates, 12% feel homosexuality is innate compared to 14% for high school graduates and 15016 for grade school graduates. In contrast, 61% of the college graduates feel homosexuality is a result of upbringing, compared to 57% of those with only a high school education and 44% for those with only a grade school education.

These results suggest that with increased education individuals are more aware of the research data on this subject. After reviewing the research on the various biological hypotheses proposed to account for homosexuality, Buss concluded: "None of the biological hypotheses has received support, and they have been discarded by most investigators. "I3

The Genetic Evidence

Nineteenth century investigators leaned towards a biological explanation of homosexuality.14 Some scientists during this period felt that it was the result of a degenerative disease of the nervous system. In view of the fact that the human embryo appears to be hermaphroditic, some researchers, including Freud, have proposed the idea that the normal psyche is bi-sexual.

Interestingly, the biological approach in understanding the cause of sexual "deviance" has focused primarily on homosexuality. There have been few studies researching the possibility that other sexual deviations such as pedophilia, necrophilia, bestiality, etc., stem from biological causes.

There is abundant evidence from research on animals that sexual behavior depends largely on sex hormones.15 There is thus some basis to assume that the cause of homosexuality in humans might be some inherited defect in either the sexual organ or sex hormones. Some early studies suggested that this was the case. For example, Kallman16 concluded from his research on a comparison between identical twins and fraternal twins that there was an inherited component in homosexuality. If homosexuality is inherited, we would expect that the incidence of homosexuality in fraternal twins (twins who develop from two separate eggs and thus do not share the same genetic pattern) would be no greater than the level found among brothers. On the other hand, we would expect to find a higher rate in identical twins, because they come from the same egg, and thus share identical genes. Kallman found far more cases where both identical twins were homosexual than for fraternal twins, supporting the hypothesis that homosexuality is at least partly inherited.

There are, though, several major shortcomings in Kallman's work, and unfortunately, some have uncritically accepted Kallman's conclusions. For example, in one article, Earnest Havemann17 stated:

France Kallman ... once managed to find 40 men, all homosexuals, who had identical twin brothers. in every case, the twin brother also turned out to be homosexual, even though the brothers had never confided in each other and had sometimes grown up apart from each other-so possibly there is some kind of inborn pattern of glandular activity of brain function, not yet recognizable by any test thus far developed which predestines some men for homosexuality.

Kallman's research can be questioned because of such problems as the representativeness of his sample and the influence of non-hereditary variables on his results. One of the chief criticisms of his conclusions is that some individuals move from heterosexuality to homosexuality during adulthood when hormonal changes are unlikely. There have also been a number of verified changes in the opposite direction. 18 If homosexuality is inherited, such shifts in sexual preference should not occur. Another problem with Kallman's research is that the relationship found was greater than could be reasonably expected. The study actually indicates that genetic control of sexuality is as dominant as genetic control over eye color or blood type.

Because a higher incidence of homosexuality may occur in twins does not conclusively demonstrate that homosexuality is inherited. It is quite possible that the powerful identification between identical twins may result in a greater tendency for both twins to engage in pre-adolescent and adolescent homosexual activities. The close association between identical twins may reduce guilt from homosexual activities that generally exists between other siblings. In summary, there may be a greater incidence of homosexuality concordance in monozygotic (identical) compared with dizygotic (fraternal) twins, but it cannot be assumed that genetic factors influence the development of homosexuality.19, 20 The social relations between monozygotic twins may be such that a higher percentage of both will be homosexuals than even dizygotic twins.

Even Kallman concluded: "The question of the possible significance of a genetic mechanism in the development of overt homosexuality may still be regarded as entirely unsettled."21

Metabolic Research

Other studies have suggested that there are metabolic differences between persons who are exclusively heterosexual and those who are exclusively homosexual. One study found that the level of etiocholanolone and androsterone was lower among homosexuals.22 There are many possible reasons for this difference, if it exists. Prolonged homosexual or heterosexual behavior could affect the breakdown of testosterone. In addition, behavioral differences such as differences in aggressively or passivity between those in a heterosexual life style and those in a homosexual life style could affect the breakdown of testosterone. Other variables such as health, diet, drug use, smoking, amount and type of sexual activity, physical and emotional stress also have to be considered. Possibly homosexuals differ from heterosexuals in general emotional responses and it is these factors which cause some hormonal differences,

Whether a person is a male or female, normal or abnormal biologically, in most cases he or she will accept the sex that he or she 
was raised, and not the sex that he or she is biologically.

The theory that the cause of homosexuality lies in high or low amounts of the sex hormones was recently examined by several researchers and found to be without foundation. Normal males have a preponderance of androgen and normal females have a preponderance of estrogen. Male homosexuals, in general, do not have a higher level of the female hormone estrogen, or less androgen, than found in heterosexual males. On the average, hormonal imbalance of any type is not more common in homosexuals than in heterosexuals. Hormonal therapy designed to correct a possible imbalance has failed to alter homosexual behavior or interest. In addition, there is an abundance of evidence that the learned psychological role, and not biological factors, determines the individual's sexual identification.

Ellis studied 48 cases of hermaphroditism and found that the great majority of cases assumed the sexual libido and sex role that accords primarily with his or her upbringing.23 This was true of both pseudohermaphrodites (individuals with congenitally malformed external genitalia resembling one sex while the gonads are those of the opposite sex) and hermaphrodites (where a person has both male and female sexual organs, or some lesser mingling of both male and female traits). Hampson studied men and women with biological sexual abnormalities, including those that were both anatomically bi-sexual or had ambiguous sexual anomalies. He concluded that when the biological sexual tendency clashed with the psychologically assigned sex role, the assigned sex role predominated.24 In other words, if a biological male was raised a female, his behavior and sexual orientation was that of a female and most always remained female in spite of effects to change his psychological sex to his biological sex. This and other studies have supported the view that homosexuality is not the result of inherited factors, but is the result of factors in the child's upbringing.25

Relative to the evidence on a possible hormonal etiology of homosexuality, Socarides26 concluded from his review of the literature that "contemporary scientific findings clearly establish that homosexuals can have endocrine dysfunctions just as can any other individuals but the androgenestrogen ratio among male homosexuals usually falls within normal limits. Large doses of endrogenes or estrogenes influence the overall sexual drive in homosexuals but cannot change the pattern."

Kolodny reported that their research found that "there is no suggestion that endocrine abnormalities will be found in a great majority of homosexuals or that endocrine dysfunction is a major factor in the pathogenesis of male homosexuality."

Brik,28 after examining the serum testosterone levels in 11 male homosexual patients, found that there was "no correlation between [sexual preference] and serum testosterone level." In addition, the homosexual subjects in Brik's study had normal testosterone levels.

Tourney et. al.29 investigated hormonal metabolism in heterosexual and homosexual men, and found no indication of disturbed endocrine functioning in homosexual males. Numerous other studies found the same or similar results.30-36

Chromosome Studies

Another area of research has looked at variations in the chromosomes as the cause of homosexuality. A normal male has an XY pattern and a normal female an XX set of chromosomes. Researchers have found many abnormal variations such as a single X (labeled XO, producing Turners Syndrome, causing mental retardation in 2001o of the cases, or Bonnevie Ultrich's Syndrome), "XXX," "XYY," "XXY," or even "XXXY" and "XXYY." These abnormal variations tend to cause deviant anatomical sex characteristics and often other problems. In addition, some individuals, such as hemaphrodites, are born with both male and female sexual organs. Fortunately, in recent years, it has become possible to examine chromosomes directly. Pritchard37 examined the chromosomes of male homosexuals, most of whom evidently had never had any heterosexual interests, and found the normal XY complement in every case. Pritchard and others have noted that there is a large body of genetic evidence against the hypothesis that homosexuality is caused by chromosomal aberrations. By means of sex chromatin and karyotype studies, several researchers examined the possibility that female chromosome constitution might be implicated. No abnormalities were found, although based on late maternal age at birth, Pritchard speculated that some chromosome abberations may be found in certain homosexual males. Klinefelter's syndrome (a condition characterized by the presence of small testes, fibrosis, hyalinization of the seminiferous tubules without involvement of leydig cells, and increase in urinary gonadotropins) is associated with an abnormality of sex chromosomes (XXY) and includes some cases with homosexual behavior, but the incidence was not higher than the population as a whole.

Kallman38,39 postulated that a polygenetically controlled disturbance in psycho-sexual maturation patterns caused homosexuality. It was felt the genetic component may affect both the ability to perceive and respond to sexual stimuli, and the ability to achieve sexual satisfaction and success. In turn, these experiences are used as integrating forces in sexual role development. As of yet, there is little supportive evidence for this hypothesis.


The above research is one of the main reasons why, according to the Gallup Poll40 "54% (of those surveyed) say homosexuals should not be hired as elementary school teachers and 65% feel gays should not be allowed to become members of the clergy." The public believe that homosexuals in these positions will influence students and youngsters in the churches and schools in a homosexual direction. It is not understood exactly what learning produces a homosexual orientation, but because it seems that this behavior is learned, it is likely that much homosexual behavior is learned from other homosexuals. In some studies, it has been found that 90% of homosexuals were introduced to homosexuality by active homosexuals .41 Rather than take any chances, most people prefer that their children not be taught by homosexual teachers or ministers.

If homosexuality is not inherited, it must either be caused by the environment or willfully adopted. A number of studies have found that homosexuality is related to poor parental relationships, certain types of parents, a history of general frustration in interpersonal relationships with persons of the opposite sex, negative early heterosexual experiences, and poor identification with the same sexed parent (often based on covert expression of the parent's superego defects).42 Simms" feels:43 "The insistence upon a 'constitutional' homosexuality is ... at the bottom of a contemporary expression of blaming God as the last resort, the shift of responsibility for one's being, and the parallel abdication of freedom."

Probably the most convincing evidence for the social learning theory are the studies which found that persons who are raised in a sex role which was different from their chromosomal sex, in most every case, became the gender role in which he or she had been reared, regardless of the true sex.44 Thus, as noted above, whether a person is a male or female, normal or abnormal biologically, in most cases he or she will accept the sex that he or she was raised, and not the sex that he or she is biologically.

Probably the most famous research which demolished the long-stranding belief that homosexuality was biological was published by Dr. Irving Bieber in 1962.45 Dr. Bieber and his researchers cited the case histories of 106 homosexuals who were treated by the Society of Medical Psychoanalysts. They found that a remarkable proportion of them had been reared by mothers who were over protective throughout their childhoods. The mothers of these homosexuals regarded their children as their "pride and joy"-to be protected from the hazards of growing up. According to this research, the mother jealously protected her boy from any girl who might show an interest in him. She often catered to his every whim and smothered him with affection, openly preferring him to her husband. Some of this attention had obvious sexual overtones, even to the extent of having him sleep in her bedroom until after he reached adolescence.

In these cases, the son evidently unconsciously replaced the husband as a love object. Importantly, though, this type of mother and a father who is cold and aloof are both necessary. If a son of an overprotective mother has a warm, affectionate father who sets a good role example and the son can look up to him, homosexuality will not develop, according to Bieber. It should be noted that some of Bieber's conclusions are now being questioned by some researchers, although this is mostly because of social trends rather than recent advances in research.

In summary, we must ask the same question that Freud46 did, viz: "If a person of the opposite sex is available, why should a male choose another male or a female another female ... or even, sometimes, a lock or hair or a piece of underclothing?" The well-known researcher on homosexuality, Socarides,47 concluded that "the answer is to be found in the developmental history of the individual." Most other researchers agree," and until we have some evidence for biological factors, we must accept the theory of eitiology that has the most empirical support.


1Craig, Alfred, 1962. "Does Homosexuality Have a Biological Basis?" One Institute Quarterly, pp. 32-35.

2Mathews, Tom and Tony Fuller and Holly Camp. "Battle Over Gay Rights." Newsweek, June 6, 1977, p. 26.

3Perry, Troy. 1972. The Lord Is My Shepherd and He Knows I'm Gay, Los Angeles, Nash Publishing, p. 10.

4Simms, Bennett. 1978. "Sex and Homosexuality." Christianity Today, February 24, 1978, pg. 25.

5Socarides, Charles W. 1978. Homosexuality. New York: Jason Aronson, p. 30-31. See also Marmon, Judd. 1975. "Sexual Disorders" in Comprehensive Textbook ofPsychiatry, Vol. 1, p. 1512, Baltimore, Maryland, Williams & Wilkens Company.

6Philpott, Kent. 1975. The Third Sex? Six Homosexuals Tell Their Stories. Logos International, Plainfield, New Jersey.

7Krafft-Ebing, Richard. 1901. Neune Studien AufDem Gebiete Der Homosexualitat, Yahr Bach fur Sex.

8Ellis, Havelock. 1938. Psychology of Sex. Emerson Books, New York.

9Mantegazza, Paolo. 1935. The Sexual Relations of Mankind. Eugenics Publishing House, New York.

10Hirschfeld, M. 1914. "Forms of Relationships of Homosexual Men and Women," Geschlect Gesund, 8:11-12.

11Glass, S. J., et al. 1940. "Sex Hormone Studies in Male Homosexuality," Endocrinology, 26:590-594.

12October, 1977, Gallup Poll Report No. 147.

13Buss, Arnold. Psychopathology. 1966. John Wiley and Sons, New York.

14Marmon, Judd. 1975. "Sexual Disorders" in Comprehensive Textbook of Psychiatry, Vol. 1, p. 1512, Williams & Wilkens Company, Baltimore, Maryland.

15Ford, Clellan and Frank Beach. 1952. Patterns of Sexual Behavior. Harper Brothers, New York, p. 226-236.

16Kallman, F. S. 1952. "Comparative Twin Studies of the Genetic Aspects of Male Homosexuality." Journal of Nervous and Mental Diseases, 115:283-298.

17Havemann, Ernest. "Scientists Search for the Answers to a Touchy and Puzzling Question. Why?" Life Magazine, Vol. 56, pg. 77, June 26, 1964.

18Kolb, Lawrence C. 1963. "Therapy of Homosexuality." In Current Psychiatric Therapies, J. Masserman, Editor, 3:131, New York: Grune and Stratton.

19Loraine, J. A., A. A. Ismael, P. A. Adamopoulos and G. A. Dove. 1970. "Endocrine Function in Male and Female Homosexuality, British Medical Journal, 4:406.

20Pritchard, M. "Homosexuality and Genetic Sex." 1962. Journal of Mental Science, 108:616-623.

21Kallman, F. J. 1963. Heredity and Health and Mental Disorders. Norton, New York.

22Money, J. 1961. "Components of Eroticism in Man: The Hormones in Relation to Sexual Morphology and Sexual Desire." Journal of Nervous and Mental Disease, 132:239-248.

23Ellis, Albert. 1962. "Sexual Psychology of Human Hermaphrodites," Psychosomatic Medicine, 7:108-125.

24Hampson, J. L. 1963. "Determinants of Sexual Orientation (Gender Role) in Humans." Canadian Psychiatric Association Journal, 8:24-34.

25Akers, Ron. 1973. Deviant Behavior: A Social Learning Approach, Belmont, California, Wadsworth Pub. Co.

26Socarides, op. cit., pg. 30-31.

27Kolodny, R. C., Masters, W. H., Hendrix, J. and Toro, G. 1971. "Plasma Testosterone and Semen Analysis in Male Homosexuals," New England Journal of Medicine, 285:1170-1178.

28Birk, L., G. H. Williams, M. Chasin and L. L. Rose. 1973. "Serum Testasterone Levels in Homosexual Men." New England Journal of Medicine, No. 23, December 6, 1973, pp. 1236-1238.

29Tourney, G., A. J. Petrilli and L. M. Hatfield. 1976. "Hormonal Relationships in Homosexual Men." American Journal of Psychiatry,132:288-290.

30Barry, H., Jr., and H. Barry 111. 1972. "Homosexuality and Testosterone," New England Journal of Medicine, 286:380-381.

31Money, J., and A. A. Ehrhart. 1972. Man and Woman, Boy and Girl. John Hopkins Press, Baltimore.

32Rainer, J. D., A. Mesnikoff, L. C. Kolb and A. Carr. 1960. " Homosexuality and Heterosexuality in Identical Twins," Psychosomatic Medicine, 22:251-259.

33Henry, G. W. "Psychogenic and Constitutional Factors in Homosexuality," 1934. Psychiatric Quarterly, p. 243-264.

34__. "Psychogenic Factors and Overt Homosexuality," 1937. American Journal of Psychiatry, 39:889-908.

35 __. "The Homosexual Delinquent," 1941. Mental Hygiene, 25:420-442.

36__ . "Sex Variance: A Study of Homosexual Patterns." 1941. Heber & Harper, New York.

37Pritchard, M. "Homosexuality and Genetic Sex." 1962. Journal of Mental Science, 108:616-623.

38Kallman, F. J. 1953. Heredity in Health and Menial Disorders. Norton, New York.

39Kallman, F. J. 1952. "Comparative Twin Studies on the Genetic Aspects of Male Homosexuality. Journal of Nervous and Mental Research Behavior, 115:283-298.

40"Majority Supports Gay Job Rights." Gallup Poll, Report No. 147, October, 1977.

41Westwood, Gordon. Society and the Homosexual. 1953. E. P. Dutton & Co., New York, p. 44.

42Kolb, Lawrence, op.cit.

43Simms, Bennett, op.cit., pg. 28.

44Money, J. "Components of Eroticism in Man: The Hormones in Relation to Sexual Morphology and Sexual Desire." 196 1. Journal of Nervous and Mental Disease, 132:239-248.

45Bieber, 1. Homosexuality. 1962. Basic Books, New York.

46Freud, Sigmund. 1905. Three Essays on the Theory of Sexuality. Standard edition, 7:125-245.

47Socarides, op.cit., pg. 35.

48Bieber, Irving. "Sexual Arousal Mechanisms in Male Homosexuals," 1975. In Sexual Behavior - Pharmacology and Biochemistry. Edited by Merton Sandler and G. L. Gessa, Raven Press, New York, pg. 291-296.

Jerry Bergman is an Assistant Professor in the college of Education (Department of Educational Foundations and Inquiry) at Bowling Green State University, Bowling Green, Ohio, where he has been since 1973. Before that, he taught Psychology and Sociology at Oakland Community College in Michigan. He has also worked in research for the court system in Oakland County Michigan. His Ph.D. is in Evaluation and Research from Wayne State University. Dr. Bergman has published over 160 articles in both general and professional journals in the areas of sociology, psychology, education and biology. He has written fourteen books and professional monographs. One of his recent monographs was published by Phi Delta Kappa, and is on the creation/evolution controversy in the schools.


Return to Top