Finger Length Ratios of Identical Twins with Discordant Sexual Orientations

Article


Watts, T. M., Holmes, L., Raines, J., Orbell, S. and Rieger, G. 2018. Finger Length Ratios of Identical Twins with Discordant Sexual Orientations. Archives of Sexual Behavior. 47 (8), p. 2435–2444.
AuthorsWatts, T. M., Holmes, L., Raines, J., Orbell, S. and Rieger, G.
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 enetically identical, differences in prenatal androgen exposure, as reflected in their different finger length ratios, might contribute to their discordance. For 18 female twin pairs, nonstraight (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 cotwins, 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.

Keywordssexual orientation; sexual differentiation; finger length ratio; 2D:4D; twins
JournalArchives of Sexual Behavior
Journal citation47 (8), p. 2435–2444
ISSN0004-0002
Year2018
PublisherSpringer for International Academy of Sex Research
Accepted author manuscript
License
File Access Level
Anyone
Digital Object Identifier (DOI)doi:10.1007/s10508-018-1262-z
Web address (URL)https://doi.org/10.1007/s10508-018-1262-z
Publication dates
Online05 Jul 2018
Publication process dates
Accepted19 Jun 2018
Deposited27 Jan 2020
FunderAmerican Institute of Bisexuality
Copyright holder© 2018 Springer
Copyright informationThis is a post-peer-review, pre-copyedit version of an article published in Archives of Sexual Behavior. The final authenticated version is available online at: https://doi.org/10.1007/s10508-018-1262-z.
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