The fraternal birth order effect (FBOE) describes the phenomenon that homosexual men tend to have a greater number of older brothers than do heterosexual men. The FBOE is a marker for an innate, biological predisposition for androphilia in genotypic males. The FBOE has been studied since the 1930s and is the most consistent biodemographic correlate of sexual orientation in men. This study sought to determine whether the FBOE applies equally to all men who have sex with men (MSM), or disproportionately to MSM whose anal intercourse behavior is predominantly receptive (Bottoms). Participants included 243 North American adult MSM who responded to advertisements posted on a Web site and other electronic media associated with the GALA festival, a quadrennial gathering of gay and lesbian choruses. Each was asked whether his anal intercourse behavior during the preceding year was predominantly receptive, predominantly penetrative, or about equally receptive and penetrative. Those who indicated their behavior was predominantly receptive were coded “Bottoms”; all others were coded “Not-Bottoms.” Participants were also surveyed as to their sibship composition. Bottoms had a significantly greater mean number of older brothers than did Not-Bottoms. There was no significant difference with respect to older or younger sisters or younger brothers. Further, the older sibling sex ratio (OSSR) for the Bottom cohort, but not for the Not-Bottom cohort, was significantly higher than the expected OSSR for the general male population (OSSR = No. older brothers/No. older sisters × 100; expected OSSR for general population = 106). Thus, late fraternal birth order was correlated with receptive anal-erotic behavior among MSM.
This is a preview of subscription content, access via your institution.
Buy single article
Instant access to the full article PDF.
Tax calculation will be finalised during checkout.
Subscribe to journal
Immediate online access to all issues from 2019. Subscription will auto renew annually.
Tax calculation will be finalised during checkout.
Bailey, J. M. (2018). The fraternal birth order effect is robust and important [Commentary]. Archives of Sexual Behavior, 47, 17–19.
Bearman, P. S., & Bruckner, H. (2002). Opposite-sex twins and same-sex adolescent attraction. American Journal of Sociology, 107(5), 1179–1205.
Bem, D. J. (2000). Exotic becomes erotic: Interpreting the biological correlates of sexual orientation. Archives of Sexual Behavior, 29, 531–548.
Blanchard, R. (1997). Birth order and sibling sex ratio in homosexual versus heterosexual males and females. Annual Review of Sex Research, 8, 27–67.
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. (2014). Detecting and correcting for family size differences in the study of sexual orientation and fraternal birth order. Archives of Sexual Behavior, 43, 845–852.
Blanchard, R. (2018a). Fraternal birth order, family size, and male homosexuality: Meta-analysis of studies spanning 25 years. Archives of Sexual Behavior, 47, 1–15.
Blanchard, R. (2018b). Response to commentaries: Meta-analysis of probability samples and other new evidence. Archives of Sexual Behavior, 47, 49–57.
Blanchard, R., & Bogaert, A. F. (1996). Homosexuality in men and number of older brothers. American Journal of Psychiatry, 153, 27–31.
Blanchard, R., Cantor, J. M., Bogaert, A. F., Breedlove, M. S., & Ellis, L. (2006). Interaction of fraternal birth order and handedness in the development of male homosexuality. Hormones and Behavior, 49, 405–414.
Blanchard, R., & Ellis, L. (2001). Birth weight, sexual orientation and the sex of preceding siblings. Journal of Biosocial Science, 33, 451–467.
Blanchard, R., & Klassen, P. (1997). H-Y antigen and homosexuality in men. Journal of Theoretical Biology, 185, 373–378.
Blanchard, R., & VanderLaan, D. P. (2015). Commentary on Kishida and Rahman (2015), including a meta-analysis of relevant studies on fraternal birth order and sexual orientation in men. Archives of Sexual Behavior, 44, 1503–1509.
Bogaert, A. F. (2006). Biological versus nonbiological older brothers and men’s sexual orientation. Proceedings of the National Academy of Sciences, 103, 10771–10774.
Bogaert, A. F., & Skorska, M. (2011). Sexual orientation, fraternal birth order, and the maternal immune hypothesis: A review. Frontiers in Neuroendocrinology, 32, 247–254.
Bogaert, A. F., Skorska, M., Wang, C., Gabriea, J., MacNeil, A. J., Hoffarth, M. R., … Blanchard, R. (2018). Male homosexuality and maternal immune responsivity to the Y-linked protein NLGN4Y. Proceedings of the National Academy of Sciences, 115(2), 302–306.
Bozkurt, A., Bozkurt, O. H., & Sonmez, I. (2015). Birth order and sibling sex ratio in a population with high fertility: Are Turkish male to female transexuals different? Archives of Sexual Behavior, 44, 1331–1337.
Cardoso, F. L. (2005). Cultural universals and differences in male homosexuality: The case of a Brazilian fishing village. Archives of Sexual Behavior, 34, 103–109.
Hare, E. H., & Moran, P. A. (1979). Parental age and birth order in homosexual patients: A replication of Slater’s study. British Journal of Psychiatry, 134, 178–182.
James, W. H. (2004). The cause(s) of the fraternal birth order effect in male homosexuality. Journal of Biosocial Science, 36, 51–59.
Jensch, K. (1941). Zur genealogie der homosexualitat [Regarding the genetics of homosexuality]. Archiv fur Psychiatrie und Nervenkrankheiten, 112, 527–540.
Lang, T. (1936). Beitrag zur Frage nach der genetisch bedingtheit der homosexualitat [A contribution regarding the question of the genetic determination of homosexuality]. Zeitschrift fur die gesamte Neurologie und Psychiatrie, 155, 702–713.
Lang, T. (1940). Studies on the genetic determination of homosexuality. Journal of Nervous and Mental Disease, 92, 55–64.
Maccoby, E. E., Doering, C. H., Jacklin, C. N., & Kraemer, H. (1979). Concentration of sex hormones in umbilical-cord blood: Their relation to sex and birth order of infant. Child Development, 50, 632–642.
Moskowitz, D. A., & Hart, T. A. (2011). The influence of physical body traits and masculinity on anal sex roles in gay and bisexual men. Archives of Sexual Behavior, 40, 835–841.
Moskowitz, D. A., Rieger, G., & Roloff, M. E. (2008). Tops, bottoms and versatiles. Sexual and Relationship Therapy, 23(3), 191–202.
Pachankis, J. E., Buttenweiser, I. G., Bernstein, L. B., & Bayles, D. O. (2013). A longitudinal, mixed methods study of sexual position identity, behavior, and fantasies among young sexual minority men. Archives of Sexual Behavior, 42, 1241–1253.
Raschka, L. B. (1995). On older fathers. American Journal of Psychiatry, 152, 1404.
Rosenberger, J. G., Reece, M., Schick, V., Herbenick, D., Novak, D. S., Vander Pol, B., & Fortenberry, J. D. (2011). Sexual behaviors and situational characteristics of most recent male-partnered sexual event among gay and bisexually identified men in the United States. Journal of Sexual Medicine, 8, 3040–3050.
Schagen, S. E., Delemarre-van de Waal, H. A., Blanchard, R., & Cohen-Kettenis, P. T. (2012). Sibling sex ratio and birth order in early-onset gender dysphoric adolescents. Archives of Sexual Behavior, 41, 541–549.
Slater, E. (1962). Birth order and maternal age of homosexuals. Lancet, 279(7220), 69–71.
Sulloway, F. J. (1996). Born to rebel: Birth order, family dynamics, and creative lives. New York, NY: Pantheon Books.
Swift-Gallant, A., Coome, L. A., Monks, D. A., & VanderLaan, D. P. (2018). Gender nonconformity and birth order in relation to anal sex role among gay men. Archives of Sexual Behavior, 47, 1041–1052.
Tan, J. Y., Pratto, F., Operario, D., & Dworkin, S. L. (2013). Sexual positioning and race-based attraction by preference for social dominance among gay Asian/Pacific Islander men living in the United States. Archives of Sexual Behavior, 44, 1431–1438.
Terman, L. M., & Miles, C. C. (1936). Sex and personality: Studies in masculinity and femininity. New York, NY: McGraw-Hill.
VanderLaan, D. P., Blanchard, R., Wood, H., Garzon, L. C., & Zucker, K. J. (2015). Birth weight and two possible types of maternal effects on male sexual orientation: A clinical study of children and adolescents referred to a gender identity service. Developmental Psychobiology, 57, 25–34.
Wall, K. M., Stephenson, R., & Sullivan, P. S. (2013). Frequency of sexual activity with most recent male partner among young, Internet-using men who have sex with men in the United States. Journal of Homosexuality, 60, 1520–1538.
Wampold, C. H. (2013). Redesigning fraternal birth order studies from top to bottom [Letter to the Editor]. Archives of Sexual Behavior, 42, 1387–1389.
Wampold, C. H. (2017). Early/late, top/bottom: Fraternal birth order and anal erotic roles of men who have sex with men (Doctoral Dissertation, Widener University). Retrieved from https://search.proquest.com/openview/4c5e839e222eeb341d0f532597fc9120/1?pq-origsite=gscholar&cbl=18750&diss=y.
Wampold, C. H. (2018). Volvivity, femininity, fraternity: Breaching the sexual orientation fortress [Commentary]. Archives of Sexual Behavior, 47, 43–46.
Weinrich, J. D., Grant, I., Jacobson, D. L., Robinson, S. R., McCutchan, J. A., & HNRC Group. (1992). Effects of recalled childhood gender nonconformity on adult genitoerotic role and AIDS exposure. Archives of Sexual Behavior, 21, 559–585.
Xu, Y., & Zheng, Y. (2017). Fraternal birth order, handedness, and sexual orientation in a Chinese population. Journal of Sex Research, 54, 10–18.
Zheng, L., Hart, T. A., & Zheng, Y. (2012). The relationship between intercourse preference positions and personality traits among gay men in China. Archives of Sexual Behavior, 41, 683–689.
Zheng, L., Hart, T. A., & Zheng, Y. (2013). Attraction to male facial masculinity in gay men in China: Relationship to intercourse preference positions and sociosexual behavior. Archives of Sexual Behavior, 42, 1223–1232.
Zheng, L., Hart, T. A., & Zheng, Y. (2015). Top/bottom sexual self-labels and empathizing-systemizing cognitive styles among gay men in China. Archives of Sexual Behavior, 44, 1431–1438.
Zietsch, B. P. (2018). Reasons for caution about the fraternal birth order effect [Commentary]. Archives of Sexual Behavior, 47, 47–48.
Zucker, K. J. (2008). Reflections on the relation between sex-typed behavior in childhood and sexual orientation in adulthood. Journal of Gay & Lesbian Mental Health, 12(1/2), 29–59.
Zucker, K. J., Green, R., Coates, S., Zuger, B., Cohen-Kettenis, P. T., Zecca, G. M., … Blanchard, R. (1997). Sibling sex ratio of boys with gender identity disorder. Journal of Child Psychology and Psychiatry, 38, 543–551.
This article reports a portion of my dissertation research that I performed while a doctoral student at the Center for Human Sexuality Studies at Widener University. I thank my dissertation chair, Donald A. Dyson, Ph.D., and the rest of my committee, Patricia B. Koch, Ph.D. and Brooke E. Wells, Ph.D., for their excellent guidance. I also thank Betsy Crane, Ph.D., who was my academic advisor at Widener, and Nicholas A. Grosskopf, Ed.D., Associate Professor, York College, City University of New York. I was paired with Dr. Grosskopf through the mentorship program at the Society for the Scientific Study of Sexuality, and he has been a mentor par excellence. Finally, I thank Jerre M. Levy, Ph.D., Professor Emerita, University of Chicago, for her many helpful insights and unflagging support.
Conflict of interest
The author declares that he has no conflict of interest.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
Human and Animal Rights
This article does not contain any studies with animals performed by any of the authors.
Informed consent was obtained from all individual participants included in the study.
About this article
Cite this article
Wampold, C.H. The Association Between Fraternal Birth Order and Anal-Erotic Roles of Men Who Have Sex with Men. Arch Sex Behav 47, 2445–2454 (2018). https://doi.org/10.1007/s10508-018-1237-0
- Sexual orientation
- Fraternal birth order
- Erotic roles
- Anal intercourse
- Coital receptivity