Genetic Influences on Male Homosexuality

Abstract

Sexual orientation, identity and desire is the final product of complex interactions between factors such as genetic influences, epigenetic, developmental pathways, both prenatal such as sex hormones, including the maternal factors acting on the foetus, and postnatal factors including shared environmental influences such as family education, social and cultural influences, and nonshared environmental influence such as unique personal experiences. Male homosexuality poses an evolutionary dilemma as it entails reduced fitness but is nevertheless, in part, influenced by genetic factors. Examining the causes of homosexuality the author investigates the Darwinian dilemma as to why genetic factors that influence homosexual nonreproductive behaviour can be maintained in the population without disappearing as expected. Sexually antagonistic selection can explain male homosexuality. A sexually antagonistic model with genetic factors partially linked to X chromosome by increasing fecundity in females and influencing homosexuality in males could be selectively balanced in the population and explain all the peculiarity of male homosexuality.

Key Concepts:

  • Homosexuality is a volatile concept that varies with culture, history and traditions. Besides a difficulty in its definition even assessing its distribution across populations poses problems of reliability still unresolved. Basically, we still cannot claim that we know the actual distribution of human homosexuality.

  • The homosexual phenotype is a complex set of emotion, behaviour and feelings influenced by a multiplicity of factors, environmental, developmental and genetic. The search of a single cause to explain the whole complexity of human homosexual phenotype seems arrived to an end.

  • In homosexuals, genetic influence interacts with a multitude of environmental, familiar, early experiences or prenatal effects such as hormonal influences, stress or immune reactions by the mother, and other biological factors such as genomic, zygotic drive and epigenetics.

  • Kin selection and avuncularity is a possibility that could compensate for the reduced fecundity of homosexuals, but most researches did not find any evidence of specific homosexual behaviour in modern society, which could promote close kin fecundity.

  • The partial influence of genetic factors on homosexuality poses an interesting Darwinian conundrum which might be resolved by a sexually antagonistic selection mechanism.

  • A sexually antagonistic selection mechanism suggests that the reduced fecundity of male homosexuals is balanced by the effect of the same genetic factors that promote fecundity in the maternal line females, thus balancing the effects on fitness and maintaining male homosexuality in the population.

Keywords: male homosexuality; bisexuality; sexual orientation; genetic influence; sexually antagonistic selection; balancing selection; fecundity; pedigrees; androphilia

Figure 1.

Male homosexuality is defined as one of the possible expression of sexual orientation that expresses sentimental and sexual attraction between individuals of the same biological sex (Kinsey et al., ).

Figure 2.

FBO distribution of male homosexuals as compared with FBO of the heterosexual control sample and the FBO distribution in the total population of Northern Italy (Camperio Ciani et al., ).

Figure 3.

Mothers, including those of first‐born son homosexuals, aunts and maternal relatives are all significantly more fecund than the corresponding heterosexuals (Iemmola and Camperio Ciani, ). Red: heterosexuals N=188 and blue: homosexuals N=250.

Figure 4.

The fecundity of mothers, maternal aunts and grandmothers of both homosexual and bisexual probands is significantly higher than the corresponding class of hetrosexual probands (Camperio et al., ).

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References

Archer J (1996) Attitudes toward homosexuals: an alternative Darwinian view. Ethology and Sociobiology 17(4): 275–280.

Arreola SG, Neilands T and Diaz R (2009) Childhood sexual abuse and the sociocultural context of sexual risk among adult Latino gay and bisexual men. American Journal of Public Health 99(Suppl 2): S432.

Bagemihl B (2000) Biological Exuberance: Animal Homosexuality and Natural Diversity (Stonewall Inn Editions). London, UK: Macmillan.

Bailey JM, Dunne MP and Martin NG (2000) Genetic and environmental influences on sexual orientation and its correlates in an Australian twin sample. Journal of Personality and Social Psychology 78: 524–536.

Bailey JM and Zucker KJ (1995) Childhood sex typed behavior and sexual orientation: a conceptual analysis and quantitative review. Developmental Psychology 31: 43–56.

Balthazart J (2011) The Biology of Homosexuality. New York: Oxford University Press.

Bancroft J (1989) Human Sexuality and its Problems. London: Churchill Livingston Elsevier Health Sciences.

Blanchard R (2001) Fraternal birth order and the maternal immune hypothesis of male homosexuality. Hormones and Behavior 40(2): 105–114.

Blanchard R (2012) Fertility in the mothers of firstborn homosexual and heterosexual men. Archives of Sexual Behavior 41(3): 551–556.

Blanchard R and Lippa RA (2007) Birth order, sibling sex ratio, handedness, and sexual orientation of male and female participants in a BBC internet research project. Archives of Sexual Behavior 36: 163–176.

Bobrow D and Bailey J (2001) Is male homosexuality maintained via kin selection? Evolution and Human Behavior 22: 361–368.

Byne W, Tobet S, Mattiace LA et al. (2001) The interstitial nuclei of the human anterior hypothalamus: an investigation of variation with sex, sexual orientation, and HIV status. Hormones and Behavior 40: 86–92.

Camperio Ciani A, Cermelli P and Zanzotto G (2008) Sexually antagonistic selection in human male homosexuality. PLoS One 3(6): 1–8.

Camperio Ciani A, Corna F and Capiluppi C (2004) Evidence for maternally inherited factors favoring male homosexuality and promoting female fecundity. Proceedings of Royal Society of London B: Biological Science 271: 2217–2221.

Camperio Ciani A, Fontanesi L, Iemmola F, Giannella E and Ferron C (2012) Factors associated with higher fecundity in female maternal relatives of homosexual men. Journal of Sexual Medicine 9: 2878–2887.

Camperio Ciani A, Iemmola F and Blecher SR (2009) Genetic factors increase fecundity in female maternal relatives of bisexual men as in homosexuals. Journal of Sexual Medicine 6(2): 449–455.

Camperio Ciani A and Pellizzari E (2012) Fecundity of paternal and maternal non‐parental female relatives of homosexual and heterosexual men. PLoS One 7(12): e51088.

Diamond M (1993) Homosexuality and bisexuality in different populations. Archives of Sexual Behavior 22(4): 291–310.

Emlen ST and Oring LW (1977) Ecology, sexual selection, and the evolution of mating systems. Science 187: 215–223.

Frisch M and Hviid A (2006) Childhood family correlates of heterosexual and homosexual marriages: a national cohort study of two million Danes. Archives of Sexual Behavior 35(5): 533–547.

Garcia‐Falgueras A and Swaab DF (2010) Sexual hormones and the brain: an essential alliance for sexual identity and sexual orientation in pediatric neuroendocrinology. In: Loche S, Cappa M, Ghizzoni L, Maghnie M and Savage MO (eds) Pediatric Neuroendocrinology. Endocr Dev, vol. 17, pp. 22–35. Basel: Karger.

Gavrilets S and Rice WR (2006) Genetic models of homosexuality: generating testable predictions. Proceedings of Royal Society of London B: Biological Science 273: 3031–3038.

Hamer DH, Hu S, Magnuson VL, Hu N and Pattattucci AM (1993) A linkage between DNA markers on the X chromosome and male sexual orientation. Science 261: 321–327.

Hewlett BS and Hewlett BL (2010). Sex and searching for children among Aka foragers and Ngandu farmers of central Africa. African Study Monographs 31(3): 107–125.

Hu S, Pattatucci AM, Patterson C et al. (1995) Linkage between sexual orientation and chromosome Xq28 in males but not in females. Nature Genetics 11(3): 248–256.

Iemmola F and Camperio Ciani AS (2009) New evidence of genetic factors influencing sexual orientation in men: female fecundity increase in the maternal line. Archives of Sexual Behavior 38: 393–399.

Jannini EA, Blanchard R, Camperio Ciani AS and Bancroft J (2010) Male homosexuality: nature or culture? Journal of Sexual Medicine 7: 3245–3253.

King M, Green J, Osborn DPJ et al. (2005) Family size in white gay and heterosexual men. Archives of Sexual Behavior 34: 117–122.

Kinsey AC, Martin CE and Pomeroy WB (1948) Sexual Behavior in the Human Male. Philadelphia: Saunders.

Långström N, Rahman Q, Carlström E and Lichtenstein P (2010) Genetic and environmental effects on same‐sex sexual behavior: a population study of twins in Sweden. Archives of Sexual Behavior 39(1): 75–80.

LeVay S (1991) A difference in hypothalamic structure between heterosexual and homosexual men. Science 253: 1034–1037.

LeVay S (2011) Gay, Straight, and the Reason Why: The Science of Sexual Orientation. New York: Oxford University Press.

Lung FW and Shu BC (2007) Father‐son attachment and sexual partner orientation in Taiwan. Comprehensive Psychiatry 48: 20–26.

Mock SE and Eibach RP (2012) Stability and change in sexual orientation identity over a 10‐year period in adulthood. Archives of Sexual Behavior 41(3): 641–648. doi:10.1007/s10508‐011‐9761‐1.

Mustanski BS, Dupree MG, Nievergelt CM et al. (2005) A genome wide scan of male sexual orientation. Human Genetics 116(4): 272–278.

Mychasiuk R, Gibb R and Kolb B (2012) Prenatal stress produces sexually dimorphic and regionally specific changes in gene expression in hippocampus and frontal cortex of developing rat offspring. Developmental Neuroscience 33(6): 531–538.

Nash G (2001) The subversive male: homosexual and bestial images on European mesolithic rock art. In: Bevan L (ed.) Indecent exposure: Sexuality, Society and the Archaeological Record, pp. 43–55. Glasgow, Scotland: Cruithne Press.

Nicolosi J (1997) Reparative Therapy of Male Homosexuality: A New Clinical Approach. Northvale, NJ: Jason Aronson, Inc.

Plomin R, DeFries JC, McClearn GE and McGuffin P (2001) Behavioral Genetics, 4th ed. New York: Worth Publishers.

Rahman Q, Collins A, Morrison M et al. (2008) Maternal inheritance and familial fecundity factors in male homosexuality. Archives of Sexual Behavior 37: 962–969.

Rice GC, Anderson N, Risch H and Ebers G (1999) Male homosexuality: absence of linkage to microsatellite markers at Xq28. Science 284: 665–667.

Rice WR, Friberg US and Gavrilets S (2012) Homosexuality as a consequence of epigenetically canalized sexual development. Quarterly Review of Biology 87(4): 343–368.

Rice WR, Friberg U and Gavrilets S (2013) Homosexuality via canalized development: a testing protocol for a new epigenetic model. Bioessays 35: 764–770.

Savin‐Williams RC (2006) Who's gay? Does it matter? Current Directions in Psychological Science 15(1): 40–44.

Schwartz G, Kim RM, Kolundzija AB, Rieger G and Sanders AR (2010) Biodemographic and physical correlates of sexual orientation in men. Archives of Sexual Behavior 39: 93–109.

Socarides CW (1995) Homosexuality: A Freedom Too Far: A Psychoanalyst Answers 1000 Questions About Causes and Cure and the Impact of the Gay Rights Movement on American Society. Phoenix, AZ: Adam Margrave Books.

Sommer V and Vasey PL (2006) Homosexual Behaviour in Animals: An Evolutionary Perspective. Boston: Cambridge University Press.

Spitzer RL (2003) Can some gay men and lesbians change their sexual orientation? 200 participants reporting a change from homosexual to heterosexual orientation. Archives of Sexual Behavior 32(5): 403–417.

Storms MD (1981) A theory of erotic orientation development. Psychological Review 88(4): 340.

VanderLaan DP and Vasey PL (2011) Male sexual orientation in independent samoa: evidence for fraternal birth order and maternal fecundity effects. Archives of Sexual Behavior 40: 495–503.

Vasey PL and VanderLaan DP (2007) Birth order and male androphilia in Samoan fa'afafine. Proceedings of the Royal Society B: Biological Sciences 274: 1437–1442.

Whitehead NE (2011) Neither genes nor choice: Same‐sex attraction is mostly a unique reaction to environmental factors. Journal of Human Sexuality 3: 81–114.

Further Reading

Bogaert AF (2006) Biological versus non‐biological older brothers and men's sexual orientation. Proceedings of the National Academy of Sciences of the USA 103(28): 10771–10774.

Hamer D and Copeland P (1994) The Science of Desire: The Search for the Gay Gene and the Biology of Behavior. New York: Simon and Schuster.

Whitehead NE and Whitehead BK (1999) My Genes Made Me Do It! Layfayette. Louisiana: Huntington House.

Wilson G and Rahman Q (2005) Born Gay. The Psychobiology of Sex Orientation. London: Peter Owen.

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Camperio Ciani, Andrea S(Apr 2014) Genetic Influences on Male Homosexuality. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0025332]