Biological Markers of Asexuality: Handedness, Birth Order, and Finger Length Ratios in Self-identified Asexual Men and Women
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.
KeywordsAsexuality Sexual orientation Finger length ratios 2D:4D Handedness Birth order
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.
- 20/20. (2006). Abstinence forever [video clip]. Available from http://www.youtube.com/watch?v=CeKGOMUVU7g&feature=PlayList&p=FD6E45790348DC2F&playnext=1&playnext_from=PL&index=30.
- American Psychiatric Association. (2000). Diagnostic and statistical manual of mental disorders (4th ed., text rev.) Washington, DC: Author.Google Scholar
- Blanchard, R., Kolla, N. J., Cantor, J. M., Klassen, P. E., Dickey, R., Kuban, M. E., & Blak, T. (2007). IQ, handedness, and pedophilia in adult male patients stratified by referral source. Sexual Abuse: A Journal of Research and Treatment, 19, 285–309.Google Scholar
- Blanchard, R., Zucker, K. J., Siegelman, M., Dickey, R., & Klassen, P. (1998). The relation of birth order to sexual orientation in men and women. Journal of Social Science, 30, 511–519.Google Scholar
- Bogaert, A. F. (2012). Understanding asexuality. Plymouth, UK: Rowman & Littlefield Publishers.Google Scholar
- Corballis, M. C. (1991). The lopsided ape: Evolution of the generative mind. New York: Oxford University Press.Google Scholar
- CNN Showbiz Tonight. (2006). A look at asexuality [video clip]. Available from http://www.youtube.com/watch?v=kkoo1lUp3ns.
- Fox News Dayside. (2006). Sex-free romance [video clip]. Available from http://www.youtube.com/watch?v=lmXXgRvotGM.
- Geschwind, D. H., Miller, B. L., DeCarli, C., & Carmelli, D. (2002). Heritability of lobar brain volumes in twins supports genetic models of cerebral laterality and handedness. Proceedings of the National Academy of Sciences of the United States of America, 99, 3176–3181.PubMedCentralCrossRefPubMedGoogle Scholar
- Hare, L., Bernard, P., Sánchez, F. J., Baird, P. N., Vilain, E., Kennedy, T., & Harley, V. R. (2009). Androgen receptor repeat length polymorphism associated with male-to-female transsexualism. Biological Psychiatry, 65, 93–96.Google Scholar
- Jay, D. (2008). Asexuality visibility and education network. Retrieved from http://www.asexuality.org/home/overview.html.
- Manning, J. T. (2002). Digit ratio: A pointer to fertility, behavior and health. New Brunswick, NJ: Rutgers University Press.Google Scholar
- Medland, S. E., Duffy, D., Spurdle, A., Wright, M., Geffen, G., Montgomery, G., & Martin, N. (2005). Opposite effects of androgen receptor CAG repeat length on increased risk of left-handedness in males and females. Behavior Genetics, 35, 735–744.Google Scholar
- Montel Williams Show. (2007). Asexuality [video clip]. Available from http://www.youtube.com/watch?v=rTD-nnUzTME.
- Pagan Westfall, S. (2004). Glad to be A. New Scientist, 184, 40–43.Google Scholar
- Rothblum, E. D., & Brehony, K. A. (1993). Boston marriages: Romantic but asexual relationships among contemporary lesbians. Amherst: University of Massachusetts Press.Google Scholar
- Seddon, B. M., & McManus, I. C. (1991). The inheritance of left-handedness: A meta-analysis. Unpublished manuscript.Google Scholar
- The View. (2006). Secrets of asexuals [video clip]. Available from http://www.youtube.com/watch?v=6kPfLYuQlL8.
- Tucker Carlson. (2006). Under the radar-asexuality [video clip]. Available from http://www.youtube.com/watch?v=Iwxo6t7XBYs.