Abstract
This study investigated the relations among sexual orientation, fraternal birth order (number of older brothers), and hand-preference. The participants were 87,798 men and 71,981 women who took part in a Web-based research project sponsored by the British Broadcasting Corporation (BBC). The results yielded some evidence confirming prior findings that non-right-handedness is associated with homosexuality in men and women, that older brothers increase the odds of homosexuality in men, and that the effect of older brothers on sexual orientation is limited to right-handed men. The evidence was weaker than in previous studies, however, probably because the usual relations among the variables of interest were partially obscured by the effects of other factors. Thus, the homosexual men and women had higher rates of non-right-handedness than their heterosexual counterparts, but the strongest handedness finding for both sexes was a marked tendency for participants who described themselves as ambidextrous also to describe themselves as bisexual. The birth order data were strongly affected by a tendency for the male participants to report an excess of older sisters, and the female participants to report an excess of older brothers. Statistical analyses confirmed that this was an artifact of the parental stopping rule, “Continue having children until you have offspring of both sexes.” In subsequent analyses, participants were divided into those who did and did not have younger siblings, on the grounds that the data of the former would be less contaminated by the stopping rule. In the former subsample, the right-handed homo/bisexual males showed the typical high ratio of older brothers to older sisters, whereas the non-right-handed homo/bisexual males did not.
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References
Bailey, J. M., & Zucker, K. J. (1995). Childhood sex-typed behavior and sexual orientation: A conceptual analysis and quantitative review. Developmental Psychology, 31, 43–55.
Ben-Porath, Y., & Welch, F. (1976). Do sex preferences really matter? Quarterly Journal of Economics, 90, 285–307.
Blanchard, R. (2004). Quantitative and theoretical analyses of the relation between older brothers and homosexuality in men. Journal of Theoretical Biology, 230, 173–187.
Blanchard, R. (2007). Sex ratio of older siblings in heterosexual and homosexual, right-handed and non-right-handed men. Archives of Sexual Behavior. DOI: 10.1007/s10508-006-9119-2.
Blanchard, R., & Bogaert, A. F. (1996). Homosexuality in men and number of older brothers. American Journal of Psychiatry, 153, 27–31.
Blanchard, R., & Bogaert, A. F. (1998). Birth order in homosexual versus heterosexual sex offenders against children, pubescents, and adults. Archives of Sexual Behavior, 27, 595–603.
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.
Blanchard, R., & Klassen, P. (1997). H-Y antigen and homosexuality in men. Journal of Theoretical Biology, 185, 373–378.
Blanchard, R., & Lippa, R. A. (2007). The sex ratio of older siblings in non-right-handed homosexual men. Archives of Sexual Behavior. DOI: 10.1007/s10508-006-9107-6.
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.
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.
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.
Chahnazarian, A. (1988). Determinants of the sex ratio at birth: Review of recent literature. Social Biology, 35, 214–235.
Clark, S. (2000). Son preference and sex composition of children: Evidence from India. Demography, 37, 95–108.
Green, R. (2000). Birth order and ratio of brothers to sisters in transsexuals. Psychological Medicine, 30, 789–795.
James, W. H. (1987). The human sex ratio: Part 1. A review of the literature. Human Biology, 59, 721–752.
James, W. H. (1998). The sex ratios of the sibs of children with psychiatric diagnoses. Journal of Child Psychology and Psychiatry, 39, 595.
Keyfitz, N. (1968). Introduction to the mathematics of population. Reading, MA: Addison-Wesley Publishing.
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.
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.
Lippa, R. A. (2003). Handedness, sexual orientation, and gender-related personality traits in men and women. Archives of Sexual Behavior, 32, 103–114.
Lippa, R. A. (2005). Sexual orientation and personality. Annual Review of Sex Research, 16, 119–153.
Mustanski, B. S., Bailey, J. M., & Kaspar, S. (2002). Dermatoglyphics, handedness, sex, and sexual orientation. Archives of Sexual Behavior, 31, 113–122.
Myers, G. C., & Roberts, J. M. (1968). A technique for measuring preferential family size and composition. Eugenics Quarterly, 15, 164–172.
Rahman, Q. (2005). Fluctuating asymmetry, second to fourth finger length ratios and human sexual orientation. Psychoneuroendocrinology, 30, 382–391.
Reimers, S. (2007). The BBC internet study: General methodology. Archives of Sexual Behavior, 36, DOI: 10.1007/s10508-006-9143-2
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.
Sloane, D. M., & Lee, C.-F. (1983). Sex of previous children and intentions for further births in the United States, 1965–1976. Demography, 20, 353–367.
Wen, X. (1993). Effect of son preference and population policy on sex ratios at birth in two provinces of China. Journal of Biosocial Science, 25, 509–521.
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.
Wood, C. H., & Bean, F. D. (1977). Offspring gender and family size: Implications from a comparison of Mexican Americans and Anglo Americans. Journal of Marriage and the Family, 39, 129–139.
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Blanchard, R., Lippa, R.A. Birth Order, Sibling Sex Ratio, Handedness, and Sexual Orientation of Male and Female Participants in a BBC Internet Research Project. Arch Sex Behav 36, 163–176 (2007). https://doi.org/10.1007/s10508-006-9159-7
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DOI: https://doi.org/10.1007/s10508-006-9159-7