The ratio of the length of the second (index) finger to the length of the fourth (ring) finger on the right hand is termed the 2D:4D ratio (Figure 1). This ratio has been shown to be different for male and female humans [17] and animals [18]. It is sexually dimorphic, with male 2D:4D ratios (≈0.95) lower than those for women (≈1.0). The 2D:4D ratio appears to be influenced by prenatal exposure to androgenic hormones in the womb.
A lower, more masculine finger ratio appears to be correlated to attitudes of gratitude [12]; greater aggression or hostility [2], [11]; increased spatial ability and sensation- seeking in men [7], [16]; lower pain perception [16]; reduced male depression [1]; greater agreeableness and less quarrelsomeness of men with women [13]; sexual attractiveness in men [4]; sperm count and testosterone levels in men [9]; increased incidences of preschool disruptive behavior in young girls but not boys [15]; faster skiing times in men and women [8]; delayed menarche in girls [10]; and a variety of other physical and psychological traits.
Higher, more feminine finger ratios appear to be correlated to depression severity in women but not men [19], personality traits in females [6], and estrogen and prolactin levels in women [9].
Finger ratios have been found to be related to career and occupational interests [5], [21], [14] and handwriting style for women but not men [3].
Animal models have indicated that androgenic steroid (especially, testosterone) exposures before birth might influence sexual orientation, and this could also be true for adult humans. The 2D:4D finger ratio was used as an indicator of prenatal androgen presence, and evidence was found that homosexuality in both sexes is more likely with higher prenatal androgen exposure [20]. Mothers previously pregnant with sons appear to have higher levels of testosterone in their bodies, thus altering the fetal development of subsequent children and increasing the likelihood of homosexuality in adulthood.
Biomarkers, indirect indications of biological phenomena such as disease, infections, or environmental exposures, come in many forms. Liquid assays identifying telltale substances circulating in the blood are some of the more promising biomarkers, with the potential to replace tissue biopsies. Based on the survey presented here, the 2D:4D ratio can be considered to be a physical biomarker for prenatal androgen exposure.
References
- A. A. Bailey and P. L. Hurd, “Depression in men is associated with more feminine finger length ratios,” Personality Individual Differences, vol. 39, no. 4, pp. 829–836, Sept. 2005.
- A. A. Bailey and P. L. Hurd, “Finger length ratio (2D:4D) correlates with physical aggression in men but not in women,” Biological Psychology, vol. 68, no. 3, pp. 215–222, Apr. 2005.
- J. R. Beech and I. C. Mackintosh, “Do differences in sex hormones affect handwriting style? Evidence from digit ratio and sex role identity as determinants of the sex of handwriting,” Personality Individual Differences, vol. 39, no. 2, pp. 459–468, July 2005.
- A. F. Bogaert, C. C. Fawcett, and L. K. Jamieson, “Attractiveness, body size, masculine sex roles and 2D:4D ratios in men,” Personality Individual Differences, vol. 47, no. 4, pp. 273–278, Sept. 2009.
- B. Hell and K. Päßler, “Are occupational interests hormonally influenced? The 2D:4D-interest nexus,” Personality Individual Differences, vol. 51, no. 4, pp. 376–380, Sept. 2011.
- B. Fink, J. T. Manning, and N. Neave, “Second to fourth digit ratio and the ‘big five’ personality factors,” Personality Individual Differences, vol. 37, no. 3, pp. 495–503, Aug. 2004.
- B. Fink, N. Neave, K. Laughton, and J. T. Manning, “Second to fourth digit ratio and sensation seeking,” Personality Individual Differences, vol. 41, no. 7, pp. 1253–1262, Nov. 2006.
- J. T. Manning, “The Ratio of 2nd to 4th digit length and performance in skiing,” J. Sports Medicine Physical Fitness, vol. 42, no. 4, pp. 446–450, Dec. 2002.
- J. T. Manning, D. Scutt, J. Wilson, and D. I. Lewis-Jones, “The ratio of 2nd to 4th digit length: A predictor of sperm numbers and concentrations of testosterone, luteinizing hormone and oestrogen,” Human Reproduction, vol. 13, no. 11, pp. 3000–3004, 1998.
- R. L. Matchock, “Low digit ratio (2D:4D) is associated with delayed menarche,” Amer. J. Human Biology, vol. 20, no. 4, pp. 487–489, 2008.
- M. H. McIntyre, E. S. Barrett, R. McDermott, D. D. P. Johnson, J. Cowden, and S. P. Rosen, “Finger length ratio (2D:4D) and sex differences in aggression during a simulated war game,” Personality Individual Differences, vol. 42, no. 4, pp. 755–764, Mar. 2007.
- M. Misiak, L. D. Kaczmarek, T. B. Kashdan, M. Zimny, H. Urban´ski, A. Zasin´ski, and D. Disabato, “Prenatal exposure to sex hormones predicts gratitude intervention use. Examination of digit ratio, motivational beliefs, and online activities,” Personality Individual Differences, vol. 77, pp. 68–73, Apr. 2015.
- D. S. Moskowitz, R. Sutton, D. C. Zuroff, and S. N. Young, “Fetal exposure to androgens, as indicated by digit ratios (2D:4D), increases men’s agreeableness with women,” Personality Individual Differences, vol. 75, pp. 97–101, Mar. 2015.
- J. V. C. Nye and E. Orel, “The influence of prenatal hormones on occupational choice: 2D:4D evidence from Moscow,” Personality Individual Differences, vol. 78, pp. 39–42, May 2015.
- B. A. Roberts and M. M. Martel, “Prenatal testosterone and preschool disruptive behavior disorders,” Personality Individual Differences, vol. 55, no. 8, pp. 962–966, Nov. 2013.
- A. Schwerdtfeger and J. Heer, “Second to fourth digit ratio (2D:4D) of the right hand is associated with nociception and augmenting-reducing,” Personality Individual Differences, vol. 45, no. 6, pp. 493–497, Oct. 2008.
- J. F. Veale, D. E. Clarke, and T. C Lomax, “Biological and psychosocial correlates of adult gender-variant identities: A review,” Personality Individual Differences, vol. 48, pp. 357–366, 2010.
- Z. Zheng and M. J. Cohn, “Developmental basis of sexually dimorphic digit ratios,” Proc. Natl. Acad. Sci., vol. 108, no. 39, pp. 16289–16294, 2011.
- K. D. Smedley, D. N. McCain, and K. J. McCain, “2D:4D digit ratio predicts depression severity for females but not for males,” Personality Individual Differences, vol. 70, pp. 136–139, Nov. 2014.
- T. J. Williams, M. E. Pepitone, S. E. Christensen, B. M. Cooke, A. D. Huberman, N. J. Breedlove, T J. Breedlove, C. L. Jordan, and S. M. Breedlove, “Finger-length ratios and sexual orientation,” Nature, vol. 404, pp. 455–456, 2000.
- S. E. Weis, A. Firker, and J. Hennig, “Associations between the second to fourth digit ratio and career interests,” Personality Individual Differences, vol. 43, pp. 485–493, 2007.