Biodemographic and Physical Correlates of Sexual Orientation in Men
To better understand sexual orientation from an evolutionary perspective, we investigated whether, compared to heterosexual men, the fewer direct descendants of homosexual men could be counterbalanced by a larger number of other close biological relatives. We also investigated the extent to which three patterns generally studied separately––handedness, number of biological older brothers, and hair-whorl rotation pattern––correlated with each other, and for evidence of replication of previous findings on how each pattern related to sexual orientation. We surveyed at Gay Pride and general community festivals, analyzing data for 894 heterosexual men and 694 homosexual men, both groups predominantly (~80%) white/non-Hispanic. The Kinsey distribution of sexual orientation for men recruited from the general community festivals approximated previous population-based surveys. Compared to heterosexual men, homosexual men had both more relatives, especially paternal relatives, and more homosexual male relatives. We found that the familiality for male sexual orientation decreased with relatedness, i.e., when moving from first-degree to second-degree relatives. We also replicated the fraternal birth order effect. However, we found no significant correlations among handedness, hair whorl rotation pattern, and sexual orientation, and, contrary to some previous research, no evidence that male sexual orientation is transmitted predominantly through the maternal line.
KeywordsSexual orientation Fecundity Evolution Birth order Handedness Hair whorl
We thank the anonymous participants for their time and cooperation. We thank Drs. J. Michael Bailey and Joan A. Linsenmeier for insightful comments on an earlier draft of the article, and the thorough reviews and helpful suggestions from the Editor and the three peer reviewers. This research was supported by a grant to RK from the Chicago Area Undergraduate Research Symposium, a Summer Undergraduate Research Grant to GS from Northwestern University, and funds from the Behavior Genetics Unit of NorthShore University HealthSystem.
- Alanko, K., Santtila, P., Harlaar, N., Witting, K., Varjonen, M., Jern, P., et al. (2009). Common genetic effects of gender atypical behavior in childhood and sexual orientation in adulthood: A study of Finnish twins. Archives of Sexual Behavior. doi: 10.1007/s10508-008-9457-3.
- Annett, M. (1985). Left, right, hand and brain: The right shift theory. London, UK: Erlbaum.Google Scholar
- Bell, A. P., & Weinberg, M. S. (1978). Homosexualities: A study of diversity among men and women. New York: Simon and Schuster.Google Scholar
- Gates, G., & Ost, J. (2004). The gay and lesbian atlas. Washington, DC: Urban Institute Press.Google Scholar
- Geschwind, D. H., Miller, B. L., DeCarli, C., & Carmelli, D. (2002). Heritability of lobar brain volumes in twins supports genetic models of cerebral laterality and handedness. Proceedings of the National Academy of Sciences of the United States of America, 99, 3176–3181.CrossRefPubMedGoogle Scholar
- Heston, L. L., & Shields, J. (1968). Homosexuality in twins: A family study and a registry study. Archives of General Psychiatry, 18, 149–160.Google Scholar
- Iemmola, F., & Camperio Ciani, A. (2008). New evidence of genetic factors influencing sexual orientation in men: Female fecundity increase in the maternal line. Archives of Sexual Behavior. doi: 10.1007/s10508-10008-19381-10506.
- James, W. H. (1987). The human sex ratio: Part I: A review of the literature. Human Biology, 59, 721–752.Google Scholar
- Jones, M. B., & Blanchard, R. (1998). Birth order and male homosexuality: Extension of Slater’s index. Human Biology, 70, 775–787.Google Scholar
- Kinsey, A. C., Pomeroy, W. B., & Martin, C. E. (1948). Sexual behavior in the human male. Philadelphia: W.B. Saunders Company.Google Scholar
- Laumann, E. O., Gagnon, J. H., Michael, R. T., & Michaels, S. (1994). The social organization of sexuality: Sexual practices in the United States. Chicago: The University of Chicago Press.Google Scholar
- Longstreth, L. E. (1980). Human handedness: More evidence of genetic involvement. Journal of Genetic Psychology, 137, 275–283.Google Scholar
- Sanders, A. R., Cao, Q., Zhang, J., Badner, J. A., Goldin, L. R., Guroff, J. J., et al. (1998). Genetic linkage study of male homosexual orientation (New Research Abstracts NR149). Toronto, Ontario, Canada: American Psychiatric Association.Google Scholar
- Wilson, E. O. (1975). Sociobiology: The new synthesis. Cambridge: Harvard University Press.Google Scholar
- Wilson, E. O. (1978). On human nature. Cambridge: Harvard University Press.Google Scholar