WebMD, published an article in 2000 titled "Pointing the Finger at Androgen as a Cause of Homosexuality," that stated:
"Previous studies have shown that, in general, a woman's index finger, or second finger (2D), is almost the same length as her ring finger, or fourth finger (4D), while a man's index finger is more often shorter than his ring finger. Since this ratio between the index and ring fingers (2D:4D) is a gender difference that can be measured very early on -- by age two -- researchers believe that prenatal androgens [male hormones] are the main factor influencing it."
Is There a Connection between Sexual Orientation and the Ratio between Second and Fourth Finger Length?
Qazi Rahman, PhD, Lecturer in Psychobiology at the University of East London, wrote in a 2005 article titled "Fluctuating Asymmetry, Second to Fourth Finger Length Ratios and Human Sexual Orientation," in Psychoneuroendocrinology:
"Homosexual men and women had significantly lower right hand 2D:4D ratios (even after controlling for handedness, height and weight differences) in comparison to heterosexuals."
Nature published the research study, "Finger-Length Ratios and Sexual Orientation," in which authors Terrance J. Williams et al. wrote:
"In women, the index finger (2D, second digit) is almost the same length as the fourth digit (4D), although it may be slightly longer or shorter; in men, the index finger is more often shorter than the fourth. The greater 2D:4D ratio in females is established in two-year-olds. Because all non-gonadal somatic sex differences in humans appear to be the result of fetal androgens that masculinize males, the sex difference in the 2D:4D ratio probably reflects the prenatal influence of androgenon males... The right-hand 2D:4D ratio of homosexual women was significantly more masculine (that is, smaller) than that of heterosexual women, and did not differ significantly from that of heterosexual men."
Biological Psychology, in the article "Sex Role Identity Related to the Ratio of Second to Fourth Digit Length in Women" by A Csatho et al. stated:
"In this study the 2D:4D ratio was measured on a sample of 46 female university students. The subjects completed the form of the Bem Sex Role Inventory (BSRI). It was found that the lower 2D:4D ratios associated significantly with higher, masculinized bias scores in BSRI indicating that 2D:4D ratio predicts the female or male self-reported sex-role identity in females."
Richard Lippa, PhD, Professor of Psychology at California State University Fullerton, wrote in the 2003 article "Are 2D:4D Finger-Length Ratios Related to Sexual Orientation? Yes for Men, No for Women," published in the Journal of Personality and Social Psychology:
"The ratio of index and ring finger lengths (2D:4D) is thought to be a marker of prenatal androgen exposure... Heterosexual men had significantly lower (more male typical) 2D:4D ratios than gay men (d = .32 and .31 for right and left hands, respectively), and these results tended to be consistent across ethnic groups... The current findings add to evidence that prenatal hormonal factors may be linked to men's sexual orientation."
Neil Whitehead, PhD, Scientific Research Consultant, as a guest writer for the National Association for Research and Treatment of Homosexuality (NARTH) website, wrote:
"Williams et al. invoke the idea of very high prenatal androgen levels (for which there is very scant evidence) to explain the difference in mean finger lengths which they find. This study is rather similar to many other reported links between homosexuality and some biologically based phenomena. Although statistical connections may be shown, only a small percentage of subjects with that biological feature actually end up homosexual."
Richard Sharpe, PhD, Programme Leader of the Medical Research Council of the Human Reproductive Sciences Unit at the University of Edinburgh, in a Mar. 2000 interview with BBC News, stated:
"No-one has actually measured the levels of androgens in foetuses or the womb - you can imagine it is difficult to do - so this [the Nature article by Williams et al.] is all speculation. It may be informed speculation, but I think when we get on to a subject as touchy as sexual orientation we need to clearly define what is speculation and what is fact."
Hormones and Behavior published a 2005 article, "Testing the Prenatal Androgen Hypothesis: Measuring Digit Ratios, Sexual Orientation, and Spatial Abilities in Adults," in which S.M. van Anders and E. Hampson wrote:
"No significant difference was found between the HS [strictly heterosexual] and NHS [not strictly heterosexual] women in the 2D:4D digit ratio."