Archives of Sexual Behavior

, Volume 43, Issue 2, pp 299–310

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

  • Morag A. Yule
  • Lori A. Brotto
  • Boris B. Gorzalka
Original Paper

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.

Keywords

Asexuality Sexual orientation Finger length ratios 2D:4D Handedness Birth order 

References

  1. American Psychiatric Association. (2000). Diagnostic and statistical manual of mental disorders (4th ed., text rev.) Washington, DC: Author.Google Scholar
  2. Berenbaum, S. A. (2002). Prenatal androgens and sexual differentiation of behavior. In E. A. Eugster & O. H. Pescovitz (Eds.), Developmental endocrinology: From research to clinical practice (pp. 293–311). Totowa, NJ: Humana Press.CrossRefGoogle Scholar
  3. Blanchard, R. (1997). Birth order and sibling sex ratio in homosexual versus heterosexual males and females. Annual Review of Sex Research, 8, 27–67.PubMedGoogle Scholar
  4. Blanchard, R. (2004). Quantitative and theoretical analyses of the relation between older brothers and homosexuality in men. Journal of Theoretical Biology, 230, 173–187.CrossRefPubMedGoogle Scholar
  5. Blanchard, R. (2008). Review and theory of handedness, birth order, and homosexuality in men. Laterality, 13, 51–70.PubMedGoogle Scholar
  6. Blanchard, R., & Bogaert, A. F. (1996). Homosexuality in men and number of older brothers. American Journal of Psychiatry, 153, 27–31.CrossRefPubMedGoogle Scholar
  7. Blanchard, R., Cantor, J. M., Bogaert, A. F., Breedlove, S. M., & Ellis, L. (2006). Interaction of fraternal birth order and handedness in the development of male homosexuality. Hormones and Behavior, 49, 405–414.CrossRefPubMedGoogle Scholar
  8. 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
  9. Blanchard, R., & Lippa, R. (2007). Birth order, sibling sex ratio, handedness, and sexual orientation of male and female participants in a BBC Internet research project. Archives of Sexual Behavior, 36, 163–176.CrossRefPubMedGoogle Scholar
  10. 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
  11. Bogaert, A. F. (1997). Birth order and sexual orientation in women. Behavioral Neuroscience, 111, 1395–1397.CrossRefPubMedGoogle Scholar
  12. Bogaert, A. F. (1998). Physical development and sexual orientation in women: Height, weight, and age of puberty comparisons. Personality and Individual Differences, 24, 115–121.CrossRefGoogle Scholar
  13. Bogaert, A. F. (2001). Handedness, criminality, and sexual offending. Neuropsychologia, 39, 465–469.CrossRefPubMedGoogle Scholar
  14. Bogaert, A. F. (2003). Interaction of older brothers and sex-typing in the prediction of sexual orientation in men. Archives of Sexual Behavior, 32, 129–134.CrossRefPubMedGoogle Scholar
  15. Bogaert, A. F. (2004). Asexuality: Prevalence and associated factors in a national probability sample. Journal of Sex Research, 41, 279–287.CrossRefPubMedGoogle Scholar
  16. Bogaert, A. F. (2006a). Biological versus nonbiological older brothers and men’s sexual orientation. Proceedings of the National Academy of Sciences of the United States of America, 103, 10771–10774.PubMedCentralCrossRefPubMedGoogle Scholar
  17. Bogaert, A. F. (2006b). Toward a conceptual understanding of asexuality. Review of General Psychology, 10, 241–250.CrossRefGoogle Scholar
  18. Bogaert, A. F. (2007). Extreme right-handedness, older brothers, and sexual orientation in men. Neuropsychology, 21, 141–148.CrossRefPubMedGoogle Scholar
  19. Bogaert, A. F. (2012). Understanding asexuality. Plymouth, UK: Rowman & Littlefield Publishers.Google Scholar
  20. Bogaert, A. F., & Blanchard, R. (1996). Physical development and sexual orientation in men: Height, weight and age of puberty differences. Personality and Individual Differences, 21, 77–84.CrossRefGoogle Scholar
  21. Bogaert, A. F., Blanchard, R., & Crosthwait, L. E. (2007). Interaction of birth order, handedness, and sexual orientation in the Kinsey interview data. Behavioral Neuroscience, 121, 845–853.CrossRefPubMedGoogle Scholar
  22. Brotto, L., Knudson, G., Inskip, J., Rhodes, K., & Erskine, Y. (2010). Asexuality: A mixed-methods approach. Archives of Sexual Behavior, 39, 599–618.CrossRefPubMedGoogle Scholar
  23. Brotto, L. A., & Yule, M. A. (2011). Physiological and subjective sexual arousal in self-identified asexual women. Archives of Sexual Behavior, 40, 699–712.CrossRefPubMedGoogle Scholar
  24. Camperio-Ciani, A., Corna, F., & Capiluppi, C. (2004). Evidence for maternally inherited factors favouring male homosexuality and promoting female fecundity. Proceedings of the Royal Society of London B, 271, 2217–2221.CrossRefGoogle Scholar
  25. Cantor, J. M. (2012). Is homosexuality a paraphilia? The evidence for and against. Archives of Sexual Behavior, 41, 237–247.PubMedCentralCrossRefPubMedGoogle Scholar
  26. Cantor, J. M., Blanchard, R., Christensen, B. K., Dickey, R., Klassen, P. E., Beckstead, A. L., et al. (2004). Intelligence, memory, and handedness in pedophilia. Neuropsychology, 18, 3–14.CrossRefPubMedGoogle Scholar
  27. Cantor, J. M., Klassen, P. E., Dickey, R., Christensen, B. K., Kuban, M. E., Blak, T., et al. (2005). Handedness in pedophilia and hebephilia. Archives of Sexual Behavior, 34, 447–459.CrossRefPubMedGoogle Scholar
  28. Caswell, N., & Manning, J. T. (2009). A comparison of finger 2D:4D by self-report direct measurement and experimenter measurement from photocopy: Methodological issues. Archives of Sexual Behavior, 38, 143–148.CrossRefPubMedGoogle Scholar
  29. Chivers, M. L., Rieger, G., Latty, E., & Bailey, J. M. (2004). A sex difference in the specificity of sexual arousal. Psychological Science, 15, 736–744.CrossRefPubMedGoogle Scholar
  30. Chivers, M. L., Seto, M. C., & Blanchard, R. (2007). Gender and sexual orientation differences in sexual response to sexual activities versus gender of actors in sexual films. Journal of Personality and Social Psychology, 93, 1108–1121.CrossRefPubMedGoogle Scholar
  31. Chivers, M. L., Seto, M. C., Lalumière, M. L., Laan, E., & Grimbos, T. (2010). Agreement of self-reported and genital measures of sexual arousal in men and women: A meta-analysis. Archives of Sexual Behaviour, 39, 5–56.CrossRefGoogle Scholar
  32. Corballis, M. C. (1991). The lopsided ape: Evolution of the generative mind. New York: Oxford University Press.Google Scholar
  33. CNN Showbiz Tonight. (2006). A look at asexuality [video clip]. Available from http://www.youtube.com/watch?v=kkoo1lUp3ns.
  34. Ellis, L., & Ames, M. A. (1987). Neurohormonal functioning and sexual orientation: A theory of homosexuality–heterosexuality. Psychological Bulletin, 101, 233–258.CrossRefPubMedGoogle Scholar
  35. Ellis, L., & Blanchard, R. (2001). Birth order, sibling sex ratio, and maternal miscarriages in homosexual and heterosexual men and women. Personality and Individual Differences, 30, 543–552.CrossRefGoogle Scholar
  36. Fox News Dayside. (2006). Sex-free romance [video clip]. Available from http://www.youtube.com/watch?v=lmXXgRvotGM.
  37. 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
  38. Gordon, A. (2002). SurveyMonkey.com-web-based survey and evaluation system. The Internet and Higher Education, 5, 83–87.CrossRefGoogle Scholar
  39. Gosling, S. D., Vazire, S., Srivastava, S., & John, O. P. (2004). Should we trust web-based studies? A comparative analysis of six preconceptions about Internet questionnaires. American Psychologist, 59, 93–104.CrossRefPubMedGoogle Scholar
  40. Green, R. (2000). Birth order and ratio of brothers to sisters in transsexuals. Psychological Medicine, 30, 789–795.CrossRefPubMedGoogle Scholar
  41. Grimbos, T., Dawood, K., Buriss, 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.CrossRefPubMedGoogle Scholar
  42. 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
  43. Jay, D. (2008). Asexuality visibility and education network. Retrieved from http://www.asexuality.org/home/overview.html.
  44. Klar, A. J. S. (2003). Human handedness and scalp hair-whorl direction development from a common genetic mechanism. Genetics, 165, 269–276.PubMedCentralPubMedGoogle Scholar
  45. Lalumière, M. L., Blanchard, R., & Zucker, K. J. (2000). Sexual orientation and handedness in men and women: A meta-analysis. Psychological Bulletin, 126, 575–592.CrossRefPubMedGoogle Scholar
  46. Lippa, R. A. (2003a). 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.CrossRefPubMedGoogle Scholar
  47. Lippa, R. A. (2003b). Handedness, sexual orientation, and gender-related personality traits in men and women. Archives of Sexual Behavior, 32, 103–114.CrossRefPubMedGoogle Scholar
  48. Manning, J. T. (2002). Digit ratio: A pointer to fertility, behavior and health. New Brunswick, NJ: Rutgers University Press.Google Scholar
  49. Manning, J. T., Churchill, A. J. G., & Peters, M. (2007). The effects of sex, ethnicity, and sexual orientation on self-measured digit ratio (2D:4D). Archives of Sexual Behavior, 36, 223–233.CrossRefPubMedGoogle Scholar
  50. Manning, J. T., Scutt, D., Wilson, J., & Lewis-Jones, D. I. (1998). The ratio of 2nd to 4th digit length: A predictor of sperm numbers and concentrations of testosterone, luteinizing hormone and oestrogen. Human Reproduction, 13, 3000–3004.CrossRefPubMedGoogle Scholar
  51. McFadden, D. (2002). Masculinization effects in the auditory system. Archives of Sexual Behavior, 31, 99–111.CrossRefPubMedGoogle Scholar
  52. 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.CrossRefPubMedGoogle Scholar
  53. 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
  54. Montel Williams Show. (2007). Asexuality [video clip]. Available from http://www.youtube.com/watch?v=rTD-nnUzTME.
  55. Mustanski, B. S., Bailey, J. M., & Kaspar, S. (2002a). Dermatoglyphics, handedness, sex, and sexual orientation. Archives of Sexual Behavior, 31, 113–122.CrossRefPubMedGoogle Scholar
  56. Mustanski, B. S., Chivers, M. L., & Bailey, J. M. (2002b). A critical review of recent biological research on human sexual orientation. Annual Review of Sex Research, 13, 89–140.PubMedGoogle Scholar
  57. Oldfield, R. C. (1971). The assessment and analysis of handedness: The Edinburgh inventory. Neuropsychologia, 9, 97–113.CrossRefPubMedGoogle Scholar
  58. Pagan Westfall, S. (2004). Glad to be A. New Scientist, 184, 40–43.Google Scholar
  59. Poston, D. L., & Baumle, A. K. (2010). Patterns of asexuality in the United States. Demographic Research, 23, 509–530.CrossRefGoogle Scholar
  60. Prause, N., & Graham, C. A. (2007). Asexuality: Classification and characterization. Archives of Sexual Behavior, 36, 341–356.CrossRefPubMedGoogle Scholar
  61. Rahman, Q., & Wilson, G. D. (2003). Born gay? The psychobiology of human sexual orientation. Personality and Individual Differences, 34, 1337–1382.CrossRefGoogle Scholar
  62. Reimers, S. (2007). The BBC Internet study: General methodology. Archives of Sexual Behavior, 36, 147–161.CrossRefPubMedGoogle Scholar
  63. Rife, D. C. (1940). Handedness, with special reference to twins. Genetics, 25, 178–186.PubMedCentralPubMedGoogle Scholar
  64. Rothblum, E. D., & Brehony, K. A. (1993). Boston marriages: Romantic but asexual relationships among contemporary lesbians. Amherst: University of Massachusetts Press.Google Scholar
  65. Seddon, B. M., & McManus, I. C. (1991). The inheritance of left-handedness: A meta-analysis. Unpublished manuscript.Google Scholar
  66. Seto, M. C. (2012). Is pedophilia a sexual orientation? Archives of Sexual Behavior, 41, 231–236.CrossRefPubMedGoogle Scholar
  67. Snabes, M. C., & Simes, S. M. (2009). Approved hormonal treatments for HSDD: An unmet medical need. Journal of Sexual Medicine, 6, 1846–1849.CrossRefPubMedGoogle Scholar
  68. Storms, M. D. (1980). Theories of sexual orientation. Journal of Personality and Social Psychology, 38, 783–792.CrossRefGoogle Scholar
  69. The View. (2006). Secrets of asexuals [video clip]. Available from http://www.youtube.com/watch?v=6kPfLYuQlL8.
  70. Tucker Carlson. (2006). Under the radar-asexuality [video clip]. Available from http://www.youtube.com/watch?v=Iwxo6t7XBYs.
  71. Williams, T. J., Pepitone, M. E., Christensen, S. E., Cooke, B. M., Huberman, A. D., Breedlove, N. J., et al. (2000). Finger-length ratios and sexual orientation. Nature, 404, 455–456.CrossRefPubMedGoogle Scholar

Copyright information

© Springer Science+Business Media New York 2013

Authors and Affiliations

  • Morag A. Yule
    • 1
  • Lori A. Brotto
    • 2
  • Boris B. Gorzalka
    • 1
  1. 1.Department of PsychologyUniversity of British ColumbiaVancouverCanada
  2. 2.Department of Obstetrics and GynaecologyUniversity of British ColumbiaVancouverCanada

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