What are finger length ratios?

Finger length ratios, specifically the ratio of the index finger (digit D2) to the ring finger (digit D4), are average measurements that can show differences between sexes. The ratio is generally greater in females than in males, meaning the lengths of the index and ring fingers are more similar in females. This ratio can be indicative of the level of androgens an individual was exposed to in utero. The effect is more pronounced on the right hand and is not dependent on handedness.

To measure this accurately, calculations must be made from the base of the finger where there's the first crease to the tip of the finger, excluding the fingernail. These measurements are not modifiable by behavior as they are established in utero and are present at birth. They are considered a primary sexual characteristic as they are established before puberty and can correlate with sexual preferences; men who self-report as homosexual often have either the typical male pattern of D2 to D4 ratio or a hypermasculinized pattern, while self-reported lesbians often have a smaller D2 to D4 ratio. It is, however, significant to remember that these are general trends and not absolutes for any individual 1 2.