On the Mathematics of the Fraternal Birth Order Effect and the Genetics of Homosexuality

Abstract

Mathematicians have always been attracted to the field of genetics. The mathematical aspects of research on homosexuality are especially interesting. Certain studies show that male homosexuality may have a genetic component that is correlated with female fertility. Other studies show the existence of the fraternal birth order effect, that is, the correlation of homosexuality with the number of older brothers. This article is devoted to the mathematical aspects of how these two phenomena are interconnected. In particular, we show that the fraternal birth order effect implies a correlation between homosexuality and maternal fecundity. Vice versa, we show that the correlation between homosexuality and female fecundity implies the increase in the probability of the younger brothers being homosexual.

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References

  1. Blanchard, R. (2004). Quantitative and theoretical analyses of the relation between older brothers and homosexuality in men. Journal of Theoretical Biology, 230, 173–187. https://doi.org/10.1016/j.jtbi.2004.04.021.

    Article  PubMed  Google Scholar 

  2. Blanchard, R. (2018). Fraternal birth oder, family size, and male homosexuality: Meta-analysis of studies spanning 25 years. Archives of Sexual Behavior, 47, 1–15. https://doi.org/10.1007/s10508-017-1007-4.

    Article  PubMed  PubMed Central  Google Scholar 

  3. Blanchard, R., & Bogaert, A. F. (1996). Homosexuality in men and number of older brothers. American Journal of Psychiatry, 153, 27–31. https://doi.org/10.1176/ajp.153.1.27.

    Article  PubMed  PubMed Central  Google Scholar 

  4. 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(28), 10771–10774. https://doi.org/10.1073/pnas.0511152103.

  5. Bogaert, A. F., Skorska, M. N., Wang, C., Gabrie, 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 of the United States of America, 115, 302–306. https://doi.org/10.1073/pnas.1705895114.

    Article  PubMed  Google Scholar 

  6. Ciani, A. C., Cermelli, P., & Zanzotto, G. (2008). Sexually antagonistic selection in human male homosexuality. PLoS ONE, 3(6), e2282. https://doi.org/10.1371/journal.pone.0002282.

    Article  Google Scholar 

  7. Iemmola, F., & Ciani, A. C. (2009). New evidence of genetic factors influencing sexual orientation in men: Female fecundity increase in the maternal line. Archives of Sexual Behavior, 38(3), 393–399. https://doi.org/10.1007/s10508-008-9381-6.

    Article  Google Scholar 

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Correspondence to Tanya Khovanova.

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The research is purely mathematical and didn’t involve any animal or human subjects.

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Khovanova, T. On the Mathematics of the Fraternal Birth Order Effect and the Genetics of Homosexuality. Arch Sex Behav 49, 551–555 (2020). https://doi.org/10.1007/s10508-019-01573-1

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Keywords

  • Fraternal birth order effect
  • Male homosexuality
  • Fecundity
  • Genetics
  • Sexual orientation