Index and ring fingers’ length linked to sexual orientation in women

Summary: Women's sexuality and finger length

A study by Watts et al. (2018) (1) suggests that women whose left hand's index and ring fingers have different lengths are more likely to be lesbians.

How male sex hormones can influence sexuality

The index (second) and ring (fourth) fingers in women tend to have the same length. In men, the index finger is the shorter one.

In case you are looking at your hands now, the evidence for masculine non-straight finger length differences is rather tenuous but this paper finds a clear correlation in sexual orientation for gay or bisexual women.

The study involved pairs of twins of both sexes with different sexual orientation, that is, one member of the pair was straight and the other one non-straight (either gay or bisexual).

For the 14 male pairs that took part in the study, the non-straight twins had "contrary to our prediction, more masculinized finger length rations than straight co-twins," but the difference was not significant.

For the 18 female pairs, the lesbian or bisexual twins had a more masculinized index to ring finger ratios than their straight co-twins. This difference only noticeable on their left hands

"Masculine ratio" means that these women's index finger is shorter than their ring finger.

The study used identical twins because their genetic makeup is identical so that any differences in their sexual orientation is not genetic and must be due to some other external factor.

Finger length ratios are due to exposure to a higher level of androgen (male sex hormones) in the womb, so it is also probable that this intrauterine hormonal exposure may also influence sexual orientation.

Updated Research during 2020

Swift-Gallant and her colleagues reported in April 20202 (2) that "These findings indicate that lesbians were, on average, exposed to greater prenatal androgen than straight women, which further indicates that greater levels of prenatal androgen predispose humans to be attracted to women in adulthood."

However, they caution that "digit ratios cannot be used to classify individual women as gay or straight."

References and Further Reading

(1) Watts TM, Holmes L, Raines J, Orbell S, Rieger G., (2018). Finger Length Ratios of Identical Twins with Discordant Sexual Orientations. Arch Sex Behav. 2018 Jul 5. doi: 10.1007/s10508-018-1262-z

(2) Ashlyn Swift-Gallant, Brandon A Johnson, Victor Di Rita, S Marc Breedlove, (2020). Through a glass, darkly: Human digit ratios reflect prenatal androgens, imperfectly. Horm Behav. 2020 Apr;120:104686. DOI: 10.1016/j.yhbeh.2020.104686