Archives of Sexual Behavior

, Volume 37, Issue 6, pp 970–976

The Sex Ratio of Older Siblings in Non-Right-Handed Homosexual Men

Original Paper


This study tested the prediction, based on prior research, that non-right-handed homosexual men will report fewer than expected older brothers. Participants were 2486 heterosexual and homosexual, right-handed and non-right-handed, male and female adults, representing five samples collected for various projects by the second author. Data on sibship composition, sexual orientation, and hand-preference were gathered in the original research using on-line (Internet) or self-administered paper-and-pencil questionnaires. The non-right-handed homosexual men reported 83 older brothers per 100 older sisters, which was significantly lower than the human sex ratio of 106 live-born males per 100 live-born females. In contrast, the right-handed homosexual men reported 125 older brothers per 100 older sisters, which was significantly higher than the expected ratio. One possible explanation of these results is that older brothers increase the odds of homosexuality in right-handed males but decrease the odds of homosexuality in non-right-handed males. A second possibility is that older brothers decrease the probability that non-right-handed homosexual males will be represented in survey research. The latter scenario could arise if the combination of some biological factor associated with older brothers and some biological factor associated with non-right-handedness is so toxic that it kills the fetus or predisposes the individual to a condition (e.g., mental retardation, major mental illness) that makes him less likely to be available for research recruitment at Gay Pride parades (etc.) than other members of the gay community.


Birth order Epidemiology Fetal wastage Handedness Homosexuality Sexual orientation Sibling sex ratio Sinistrality 


  1. Berglin, C.-G. (1982). Birth order as a quantitative expression of date of birth. Journal of Epidemiology and Community Health, 36, 298–302.PubMedCrossRefGoogle Scholar
  2. Birtchnell, J. (1971). Birth rank and mental illness. Nature, 234, 485–487.PubMedCrossRefGoogle Scholar
  3. Bishop, D. V. M. (1990). Handedness and developmental disorder. Oxford: Blackwell Scientific Publications.Google Scholar
  4. Blanchard, R. (2004). Quantitative and theoretical analyses of the relation between older brothers and homosexuality in men. Journal of Theoretical Biology, 230, 173–187.PubMedCrossRefGoogle Scholar
  5. Blanchard, R., & Bogaert, A. F. (1996). Homosexuality in men and number of older brothers. American Journal of Psychiatry, 153, 27–31.PubMedGoogle Scholar
  6. Blanchard, R., Cantor, J. M., Bogaert, A. F., Breedlove, S. M., & Ellis, L. (2006). Interaction of fraternal birth order and handedness in the development of male homosexuality. Hormones and Behavior, 49, 405–414.PubMedCrossRefGoogle Scholar
  7. Blanchard, R., Zucker, K. J., Bradley, S. J., & Hume, C. S. (1995). Birth order and sibling sex ratio in homosexual male adolescents and probably prehomosexual feminine boys. Developmental Psychology, 31, 22–30.CrossRefGoogle Scholar
  8. Bogaert, A. F. (2006). Biological versus nonbiological older brothers and men’s sexual orientation. Proceedings of the National Academy of Sciences of the United States of America, 103, 10771–10774.PubMedCrossRefGoogle Scholar
  9. Bogaert, A. F., Blanchard, R., & Crosthwait, L. E. (2006). Interaction of birth order, handedness, and sexual orientation in the Kinsey interview data. Manuscript in preparation.Google Scholar
  10. Camperio-Ciani, A., Corna, F., & Capiluppi, C. (2004). Evidence for maternally inherited factors favouring male homosexuality and promoting female fecundity. Proceedings of the Royal Society of London B, 271, 2217–2221.CrossRefGoogle Scholar
  11. Cantor, J. M., Klassen, P. E., Dickey, R., Christensen, B. K., Kuban, M. E., Blak, T., et al. (2005). Handedness in pedophilia and hebephilia. Archives of Sexual Behavior, 34, 447–459.PubMedCrossRefGoogle Scholar
  12. Chahnazarian, A. (1988). Determinants of the sex ratio at birth: Review of recent literature. Social Biology, 35, 214–235.PubMedGoogle Scholar
  13. Cobb, J. A. (1914). The alleged inferiority of the first-born. Eugenics Review, 5, 357–359.Google Scholar
  14. Green, R. (2000). Birth order and ratio of brothers to sisters in transsexuals. Psychological Medicine, 30, 789–795.PubMedCrossRefGoogle Scholar
  15. Hare, E. H., & Price, J. S. (1969). Birth order and family size: Bias caused by changes in birth rate. British Journal of Psychiatry, 115, 647–657.PubMedCrossRefGoogle Scholar
  16. Hare, E. H., & Price, J. S. (1974). Birth order and birth rate bias: Findings in a representative sample of the adult population of Great Britain. Journal of Biosocial Science, 6, 139–150.Google Scholar
  17. Jagers, P. (1982). How probable is it to be first born? and other branching-process applications to kinship problems. Mathematical Biosciences, 59, 1–15.CrossRefGoogle Scholar
  18. James, W. H. (1987). The human sex ratio: Part 1. A review of the literature. Human Biology, 59, 721–752.Google Scholar
  19. King, M., Green, J., Osborn, D. P. J., Arkell, J., Hetherton, J., & Pereira, E. (2005). Family size in white gay and heterosexual men. Archives of Sexual Behavior, 34, 117–122.PubMedCrossRefGoogle Scholar
  20. Lalumière, M. L., Blanchard, R., & Zucker, K. J. (2000). Sexual orientation and handedness in men and women: A meta-analysis. Psychological Bulletin, 126, 575–592.PubMedCrossRefGoogle Scholar
  21. Lippa, R. A. (2003a). Are 2D:4D finger-length ratios related to sexual orientation? Yes for men, no for women. Journal of Personality and Social Psychology, 85, 179–188.PubMedCrossRefGoogle Scholar
  22. Lippa, R. A. (2003b). Handedness, sexual orientation, and gender-related personality traits in men and women. Archives of Sexual Behavior, 32, 103–114.PubMedCrossRefGoogle Scholar
  23. Lippa, R. A. (2006a). Is high sex drive associated with increased sexual attraction to both sexes? It depends on whether you’re male or female. Psychological Science, 17, 46–52.PubMedCrossRefGoogle Scholar
  24. Lippa, R. A. (2006b, April). Childhood gender nonconformity and adult personality in heterosexual and homosexual men and women. Poster presented at the Gender Development Conference, San Francisco, CA.Google Scholar
  25. Mustanski, B. S., Bailey, J. M., & Kaspar, S. (2002). Dermatoglyphics, handedness, sex, and sexual orientation. Archives of Sexual Behavior, 31, 113–122.PubMedCrossRefGoogle Scholar
  26. Price, J. S., & Hare, E. H. (1969). Birth order studies: Some sources of bias. British Journal of Psychiatry, 115, 633–646.PubMedCrossRefGoogle Scholar
  27. Rahman, Q. (2005). Fluctuating asymmetry, second to fourth finger length ratios and human sexual orientation. Psychoneuroendocrinology, 30, 382–391.PubMedCrossRefGoogle Scholar
  28. Robinson, S. J., & Manning, J. T. (2000). The ratio of 2nd to 4th digit length and male homosexuality. Evolution and Human Behavior, 21, 333–345.PubMedCrossRefGoogle Scholar
  29. Williams, T. J., Pepitone, M. E., Christensen, S. E., Cooke, B. M., Huberman, A. D., Breedlove, N. J., et al. (2000). Finger-length ratios and sexual orientation. Nature, 404, 455–456.PubMedCrossRefGoogle Scholar
  30. Zucker, K. J., Beaulieu, N., Bradley, S. J., Grimshaw, G. M., & Wilcox, A. (2001). Handedness in boys with gender identity disorder. Journal of Child Psychology and Psychiatry, 42, 767–776.PubMedCrossRefGoogle Scholar
  31. Zucker, K. J., Green, R., Coates, S., Zuger, B., Cohen-Kettenis, P. T., Zecca, G. M., et al. (1997). Sibling sex ratio of boys with gender identity disorder. Journal of Child Psychology and Psychiatry, 38, 543–551.PubMedCrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media, LLC 2006

Authors and Affiliations

  1. 1.Law and Mental Health ProgramCentre for Addiction and Mental Health, College Street SiteTorontoCanada
  2. 2.Department of PsychiatryUniversity of TorontoTorontoCanada
  3. 3.Department of PsychologyCalifornia State UniversityFullertonUSA

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