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Biological Markers of Asexuality: Handedness, Birth Order, and Finger Length Ratios in Self-identified Asexual Men and Women

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Abstract

Human asexuality is defined as a lack of sexual attraction to anyone or anything and it has been suggested that it may be best conceptualized as a sexual orientation. Non-right-handedness, fraternal birth order, and finger length ratio (2D:4D) are early neurodevelopmental markers associated with sexual orientation. We conducted an Internet study investigating the relationship between self-identification as asexual, handedness, number of older siblings, and self-measured finger-lengths in comparison to individuals of other sexual orientation groups. A total of 325 asexuals (60 men and 265 women; M age, 24.8 years), 690 heterosexuals (190 men and 500 women; M age, 23.5 years), and 268 non-heterosexuals (homosexual and bisexual; 64 men and 204 women; M age, 29.0 years) completed online questionnaires. Asexual men and women were 2.4 and 2.5 times, respectively, more likely to be non-right-handed than their heterosexual counterparts and there were significant differences between sexual orientation groups in number of older brothers and older sisters, and this depended on handedness. Asexual and non-heterosexual men were more likely to be later-born than heterosexual men, and asexual women were more likely to be earlier-born than non-heterosexual women. We found no significant differences between sexual orientation groups on measurements of 2D:4D ratio. This is one of the first studies to test and provide preliminary empirical support for an underlying neurodevelopmental basis to account for the lack of sexual attraction characteristic of asexuality.

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Notes

  1. Identical analyses performed on all ethnicities in this sample revealed a similar pattern of results.

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Acknowledgments

Funding for this study was from a University of British Columbia Hampton Research Grant awarded to L.A.B. M.A.Y. was funded by a Predoctoral Fellowship. We wish to thank Martin L. Lalumière for his generous statistical assistance.

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Authors and Affiliations

  1. Department of Psychology, University of British Columbia, Vancouver, BC, Canada

    Morag A. Yule & Boris B. Gorzalka

  2. Department of Obstetrics and Gynaecology, University of British Columbia, 2775 Laurel Street, 6th Floor, Vancouver, BC, V5Z 1M9, Canada

    Lori A. Brotto

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  1. Morag A. Yule
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  2. Lori A. Brotto
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  3. Boris B. Gorzalka
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Correspondence to Lori A. Brotto.

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Yule, M.A., Brotto, L.A. & Gorzalka, B.B. Biological Markers of Asexuality: Handedness, Birth Order, and Finger Length Ratios in Self-identified Asexual Men and Women. Arch Sex Behav 43, 299–310 (2014). https://doi.org/10.1007/s10508-013-0175-0

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