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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

Abstract

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.

Keywords

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

Notes

Funding

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.

References

  1. Allaway, H. C., Bloski, T. G., Pierson, R. A., & Lujan, M. E. (2009). Digit ratios (2D:4D) determined by computer-assisted analysis are more reliable than those using physical measurements, photocopies, and printed scans. American Journal of Human Biology, 21, 365–370.  https://doi.org/10.1002/ajhb.20892.CrossRefPubMedPubMedCentralGoogle Scholar
  2. Auyeung, B., Baron-Cohen, S., Ashwin, E., Knickmeyer, R., Taylor, K., Hackett, G., et al. (2009). Fetal testosterone predicts sexually differentiated childhood behavior in girls and in boys. Psychological Science, 20, 144–148.  https://doi.org/10.1111/j.1467-9280.2009.02279.x.CrossRefPubMedPubMedCentralGoogle Scholar
  3. Bailey, J. M., Dunne, M. P., & Martin, N. G. (2000). Genetic and environmental influences on sexual orientation and its correlates in an Australian twin sample. Journal of Personality and Social Psychology, 78, 524–536.  https://doi.org/10.1037/0022-3514.78.3.524.CrossRefPubMedPubMedCentralGoogle Scholar
  4. Bailey, J. M., Vasey, P. L., Diamond, L. M., Breedlove, S. M., Vilain, E., & Epprecht, M. (2016). Sexual orientation, controversy, and science. Psychological Science in the Public Interest, 17, 45–101.  https://doi.org/10.1177/1529100616637616.CrossRefPubMedPubMedCentralGoogle Scholar
  5. Berenbaum, S. A., Bryk, K. K., Nowak, N., Quigley, C. A., & Moffat, S. (2009). Fingers as a marker of prenatal androgen exposure. Endocrinology, 150, 5119–5124.  https://doi.org/10.1210/en.2009-0774.CrossRefPubMedPubMedCentralGoogle Scholar
  6. Breedlove, S. M. (2010). Minireview: Organizational hypothesis: Instances of the fingerpost. Endocrinology, 151, 4116–4122.  https://doi.org/10.1210/en.2010-0041.CrossRefPubMedPubMedCentralGoogle Scholar
  7. Breedlove, S. M. (2017). Prenatal influences on human sexual orientation: Expectations versus data. Archives of Sexual Behavior, 46, 1583–1592.  https://doi.org/10.1007/s10508-016-0904-2.CrossRefPubMedPubMedCentralGoogle Scholar
  8. Brown, W. M., Hines, M., Fane, B. A., & Breedlove, S. M. (2002). Masculinized finger length patterns in human males and females with congenital adrenal hyperplasia. Hormones and Behavior, 42, 380–386.  https://doi.org/10.1006/hbeh.2002.1830.CrossRefPubMedPubMedCentralGoogle Scholar
  9. Ciumas, C., Hirschberg, A. L., & Savic, I. (2009). High fetal testosterone and sexually dimorphic cerebral networks in females. Cerebral Cortex, 19, 1167–1174.  https://doi.org/10.1093/cercor/bhn160.CrossRefPubMedGoogle Scholar
  10. Dittmann, R. W., Kappes, M. E., & Kappes, M. H. (1992). Sexual behavior in adolescent and adult females with congenital adrenal hyperplasia. Psychoneuroendocrinology, 17, 153–170.  https://doi.org/10.1016/0306-4530(92)90054-B.CrossRefGoogle Scholar
  11. Gobrogge, K. L., Breedlove, S. M., & Klump, K. L. (2008). Genetic and environmental influences on 2D:4D finger length ratios: A study of monozygotic and dizygotic male and female twins. Archives of Sexual Behavior, 37, 112–118.  https://doi.org/10.1007/s10508-007-9272-2.CrossRefPubMedGoogle Scholar
  12. Grimbos, T., Dawood, K., Burriss, R. P., Zucker, K. J., & Puts, D. A. (2010). Sexual orientation and the second to fourth finger length ratio: A meta-analysis in men and women. Behavioral Neuroscience, 124, 278–287.  https://doi.org/10.1037/a0018764.CrossRefPubMedPubMedCentralGoogle Scholar
  13. Hall, L. S., & Love, C. T. (2003). Finger-length ratios in female monozygotic twins discordant for sexual orientation. Archives of Sexual Behavior, 32, 23–28.  https://doi.org/10.1023/A:1021837211630.CrossRefPubMedGoogle Scholar
  14. Hines, M. (2011). Prenatal endocrine influences on sexual orientation and on sexually differentiated childhood behavior. Frontiers in Neuroendocrinology, 32, 170–182.  https://doi.org/10.1016/j.yfrne.2011.02.006.CrossRefPubMedPubMedCentralGoogle Scholar
  15. Hines, M., Ahmed, S. F., & Hughes, I. A. (2003). Psychological outcomes and gender-related development in complete androgen insensivity syndrome. Archives of Sexual Behavior, 32, 93–101.  https://doi.org/10.1023/A:1022492106974.CrossRefPubMedPubMedCentralGoogle Scholar
  16. Hines, M., Golombok, S., Rust, J., Johnston, K. J., & Golding, J. (2002). Testosterone during pregnancy and gender role behavior of preschool children: A longitudinal, population study. Child Development, 73, 1678–1687.  https://doi.org/10.2307/3696409.CrossRefPubMedGoogle Scholar
  17. Hiraishi, K., Sasaki, S., Shikishima, C., & Ando, J. (2012). The second to fourth digit ratio (2D:4D) in a Japanese twin sample: Heritability, prenatal hormone transfer, and association with sexual orientation. Archives of Sexual Behavior, 41, 711–724.  https://doi.org/10.1007/s10508-011-9889-z.CrossRefPubMedGoogle Scholar
  18. Hönekopp, J., & Watson, S. (2010). Meta‐analysis of digit ratio 2D: 4D shows greater sex difference in the right hand. American Journal of Human Biology22(5), 619–630.  https://doi.org/10.1002/ajhb.21054.CrossRefPubMedGoogle Scholar
  19. Kinsey, A. C., Pomeroy, W. B., & Martin, C. E. (1948). Sexual behavior in the human male. Philadelphia: Saunders.Google Scholar
  20. Lippa, R. A. (2003). Are 2D:4D finger-length ratios related to sexual orientation? Yes for men, no for women. Journal of Personality and Social Psychology, 85, 179–188.  https://doi.org/10.1037/0022-3514.85.1.179.CrossRefPubMedGoogle Scholar
  21. Lippa, R. A. (2005). Sexual orientation and personality. Annual Review of Sex Research, 16, 119–153.  https://doi.org/10.1080/10532528.2005.10559831.CrossRefGoogle Scholar
  22. Loken, E., & Gelman, A. (2017). Measurement error and the replication crisis. Science, 355, 584.  https://doi.org/10.1126/science.aal3618.CrossRefPubMedGoogle Scholar
  23. Manning, J. T. (2011). Resolving the role of prenatal sex steroids in the development of digit ratio. Proceedings of the National Academy of Sciences, 108, 16143–16144.  https://doi.org/10.1073/pnas.1113312108.CrossRefGoogle Scholar
  24. Manning, J., Kilduff, L., Cook, C., Crewther, B., & Fink, B. (2014). Digit ratio (2D:4D): A biomarker for prenatal sex steroids and adult sex steroids in challenge situations. Frontiers in Endocrinology.  https://doi.org/10.3389/fendo.2014.00009.CrossRefPubMedPubMedCentralGoogle Scholar
  25. McFadden, D., Loehlin, J. C., Breedlove, S. M., Lippa, R. A., Manning, J. T., & Rahman, Q. (2005). A reanalysis of five studies on sexual orientation and the relative length of the 2nd and 4th fingers (the 2D: 4D ratio). Archives of Sexual Behavior, 34, 341–356.  https://doi.org/10.1007/s10508-005-3123-9.CrossRefPubMedGoogle Scholar
  26. McFadden, D., & Shubel, E. (2002). Relative lengths of fingers and toes in human males and females. Hormones and Behavior, 42, 492–500.  https://doi.org/10.1006/hbeh.2002.1833.CrossRefPubMedGoogle Scholar
  27. Merke, D. P., & Bornstein, S. R. (2005). Congenital adrenal hyperplasia. Lancet, 365, 2125–2136.  https://doi.org/10.1016/S0140-6736(05)66736-0.CrossRefPubMedGoogle Scholar
  28. Meyer-Bahlburg, H. F. L., Dolezal, C., Baker, S. W., & New, M. I. (2008). Sexual orientation in women with classical or non-classical congenital adrenal hyperplasia as a function of degree of prenatal androgen excess. Archives of Sexual Behavior, 37, 85–99.  https://doi.org/10.1007/s10508-007-9265-1.CrossRefPubMedPubMedCentralGoogle Scholar
  29. Motta-Mena, N. V., & Puts, D. A. (2017). Endocrinology of human female sexuality, mating, and reproductive behavior. Hormones and Behavior, 91, 19–35.  https://doi.org/10.1016/j.yhbeh.2016.11.012.CrossRefPubMedPubMedCentralGoogle Scholar
  30. Ökten, A., Kalyoncu, M., & Yariş, N. (2002). The ratio of second- and fourth-digit lengths and congenital adrenal hyperplasia due to 21-hydroxylase deficiency. Early Human Development, 70, 47–54.  https://doi.org/10.1016/S0378-3782(02)00073-7.CrossRefPubMedGoogle Scholar
  31. Pasterski, V., Acerini, C. L., Dunger, D. B., Ong, K. K., Hughes, I. A., Thankamony, A., et al. (2015). Postnatal penile growth concurrent with mini-puberty predicts later sex-typed play behavior: Evidence for neurobehavioral effects of the postnatal androgen surge in typically developing boys. Hormones and Behavior, 69, 98–105.  https://doi.org/10.1016/j.yhbeh.2015.01.002.CrossRefPubMedGoogle Scholar
  32. Patterson, P. H. (2007). Maternal effects on schizophrenia risk. Science, 318, 576.  https://doi.org/10.1126/science.1150196.CrossRefPubMedGoogle Scholar
  33. Price, T. S., Freeman, B., Craig, I., Petrill, S. A., Ebersole, L., & Plomin, R. (2012). Infant zygosity can be assigned by parental report questionnaire data. Twin Research, 3, 129–133.  https://doi.org/10.1375/twin.3.3.129.CrossRefGoogle Scholar
  34. Putz, D. A., Gaulin, S. J. C., Sporter, R. J., & McBurney, D. H. (2004). Sex hormones and finger length: What does 2D:4D indicate? Evolution and Human Behavior, 25, 182–199.  https://doi.org/10.1016/j.evolhumbehav.2004.03.005.CrossRefGoogle Scholar
  35. Rahman, Q. (2005). The neurodevelopment of human sexual orientation. Neuroscience and Biobehavioral Reviews, 29, 1057–1066.  https://doi.org/10.1016/j.neubiorev.2005.03.002.CrossRefPubMedGoogle Scholar
  36. Rieger, G., Linsenmeier, J. A. W., Gygax, L., & Bailey, J. M. (2008). Sexual orientation and childhood gender nonconformity: Evidence from home videos. Developmental Psychology, 44, 46–58.  https://doi.org/10.1037/0012-1649.44.1.46.CrossRefPubMedGoogle Scholar
  37. Robinson, S. J., & Manning, J. T. (2000). The ratio of 2nd to 4th digit length and male homosexuality. Evolution and Human Behavior, 21, 333–345.  https://doi.org/10.1016/S1090-5138(00)00052-0.CrossRefPubMedGoogle Scholar
  38. Watts, T. M., Holmes, L., Raines, J., Orbell, S., & Rieger, G. (2018). Gender nonconformity of identical twins with discordant sexual orientations: Evidence from childhood photographs. Developmental Psychology, 54, 788–801.  https://doi.org/10.1037/dev0000461.CrossRefPubMedGoogle Scholar
  39. Zheng, Z., & Cohn, M. J. (2011). Developmental basis of sexually dimorphic digit ratios. Proceedings of the National Academy of Sciences, 108, 16289–16294.  https://doi.org/10.1073/pnas.1108312108.CrossRefGoogle Scholar
  40. Zucker, K. J., Bradley, S. J., Oliver, G., Blake, J., Fleming, S., & Hood, J. (1996). Psychosexual development of women with congenital adrenal hyperplasia. Hormones and Behavior, 30, 300–318.  https://doi.org/10.1006/hbeh.1996.0038.CrossRefPubMedGoogle Scholar

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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