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

  • Tanya KhovanovaEmail author
Original Paper


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.


Fraternal birth order effect Male homosexuality Fecundity Genetics Sexual orientation 


Compliance with Ethical Standards

Conflict of interest

The author declare that she has no conflict of interest.

Ethical Approval

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


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Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Department of MathematicsMassachusetts Institute of TechnologyCambridgeUSA

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