Have you ever observed the length of your fingers? Particularly your index finger and your ring finger. Turns out, this information might help in predicting whether a woman is attracted to the same or the opposite sex.

Usually, the index and ring fingers are nearly the same length in women. On the other hand (pardon the pun), there was often a noticeable difference in length between the two fingers in men.

Eighteen pairs of female identical twins were recruited for a study at the University of Essex, England. In each pair of twins, one woman was straight and one was a lesbian.

On average, the research team found a difference in the lengths of their index and ring fingers in the lesbian participants. But this was not seen in the straight participants. According to the researchers, exposure to higher levels of testosterone in the womb may explain this.

“Because identical twins, who share 100 percent of their genes, can differ in their sexual orientations, factors other than genetics must account for the differences,” said study author Dr. Tuesday Watts, a lecturer in the department of psychology at Essex.

“Research suggests that our sexuality is determined in the womb and is dependent on the amount of male hormone we are exposed to or the way our individual bodies react to that hormone, with those exposed to higher levels of testosterone being more likely to be bisexual or homosexual.”

Thanks to the association between hormone levels and the difference in finger lengths, you are more likely to guess the sexual orientation of a woman correctly if you observe their hands.

Conducted by Watts and her colleague Dr. Gerulf Rieger, findings of the study titled “Finger Length Ratios of Identical Twins with Discordant Sexual Orientations” was published in the Archives of Sexual Behaviour.

The research team also conducted the same experiment with 14 pairs of male identical twins where one was straight and one was gay. However, they found no such association in this case.

But past research has suggested the difference in lengths between the two fingers might help men predict something else — penis size. Once again, this was believed to be tied to testosterone exposure in the womb.

In one study, researchers at Gachon University Gil Hospital in South Korea studied close to 150 male volunteers. The bigger the difference between the index and ring finger in a man, the bigger his penis was likely to be.

“Based on this evidence, we suggest that digit ratio can predict adult penile size and that the effects of prenatal testosterone may in part explain the differences in adult penile length,” the researchers wrote in the paper published in 2011.

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