Gay or straight? It’s all there in your fingers

Sounds complicated but there’s a fairly simple biological explanation.

In women, the index finger is about the same length as the ring finger. In men, the ring finger is considerably longer. This difference in the finger lengths in the two sexes is apparent from infancy and is determined by the levels of male hormones the foetus is exposed to during its development in the womb.

In animals, prenatal exposure to the male sex hormone, testosterone, is known to influence sexual orientation. Since it’s difficult to measure foetal hormone levels in humans, the researchers measured these levels by the length of a person’s fingers.

Breedlove and his colleagues wanted to know if gays had different finger length ratios from heterosexuals so they surveyed 720 adults in San Francisco. They also collected information about gender, age, sexual orientation and older siblings, and of course, measured the lengths of the volunteers’ fingers very carefully.

The results were striking. In lesbians, the index to ring finger ratio was similar to that in heterosexual men. In other words, their ring finger was longer than their index finger, a quality usually seen in heterosexual men. This suggests that gay women were exposed to higher than average levels of male hormones before birth.

The difference in men was less stark. The index and ring fingers difference in gay men was not very different from that in heterosexual men. So the researchers fell back on studies done in the ’90s that showed the more older brothers a man had, the more likely he was to be gay.

They then sorted the volunteers according to numbers of older brothers they had. They found that all the men who had two or more older brothers had significantly smaller differences in finger lengths.

Simply put, their ring and index finger were the same length, as in heterosexual women. The study concludes that homosexuality is partly due to higher levels of prenatal testosterone in both men and women.

But Breedlove stresses that foetal hormones alone don’t determine sexuality. Most first-born males have indistinguishable differences in the lengths of the ring and index fingers, whether they are gay or straight. So other factors also come into play, as they must do in bisexuals, who are completely ignored in this elaborate finger play.

Ring finger longer than index finger

Women: Lesbian
Men: Heterosexual
Both fingers the same length
Women:Heterosexual
Men: Gay