Archives of Sexual Behavior

, Volume 47, Issue 8, pp 2435–2444 | Cite as

Finger Length Ratios of Identical Twins with Discordant Sexual Orientations

  • Tuesday M. WattsEmail author
  • Luke Holmes
  • Jamie Raines
  • Sheina Orbell
  • Gerulf Rieger
Original Paper


A proposed marker of prenatal androgen exposure is the ratio of the index finger to ring finger (2D:4D). Within each sex, this ratio may be lower for those who were exposed to higher levels of androgens and become attracted to women, as compared to those who were exposed to lower levels of androgens and become attracted to men. We examined these patterns in identical twins with discordant sexual orientations. Because these twins are genetically identical, differences in prenatal androgen exposure, as reflected in their different finger length ratios, might contribute to their discordance. For 18 female twin pairs, non-straight (bisexual or lesbian) twins had significantly lower, or more masculinized, 2D:4D ratios than their straight co-twins, but only in the left hand. For 14 male pairs, non-straight twins had, contrary to our prediction, more masculinized finger length ratios than straight co-twins, but this difference was not significant. A reanalysis of present and previous data (Hall & Love, 2003; Hiraishi, Sasaki, Shikishima, & Ando, 2012) suggested that these patterns were robust. Furthermore, males had more masculinized 2D:4D ratios than females. This sex difference did not vary by sexual orientation.


Sexual orientation Sexual differentiation Finger length ratio 2D:4D Twins 



This research was funded by the American Institute of Bisexuality.

Compliance with Ethical Standards

Conflict of interest

All authors declare that they have no conflict of interest.

Ethical Approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The University of Essex’s Ethics Committee approved this study (“GR1303”).

Informed Consent

Informed consent was obtained from all individual participants included in the study.


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Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2018

Authors and Affiliations

  • Tuesday M. Watts
    • 1
    Email author
  • Luke Holmes
    • 1
  • Jamie Raines
    • 1
  • Sheina Orbell
    • 1
  • Gerulf Rieger
    • 1
  1. 1.Department of PsychologyUniversity of EssexColchesterUK

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