Effects of prenatal sex steroids on fertility, behavior, and health.
Digit ratio (or 2D:4D), i.e., the relative length of the 2nd digit (“index finger”; 2D) and the 4th digit (“ring finger”; 4D) has attracted the attention of scholars for many years (Baker 1888; Minami 1952; Phelps 1952). At the center of this interest lies the sex difference and ethnic variation in 2D:4D, and the appearance of the sexual dimorphism in 2D:4D at a very early stage in ontogeny.
Digit ratio is sexually dimorphic with males typically having longer 4th digits relative to 2nd digits than do females (male 2D:4D < female 2D:4D). The sex difference in 2D:4D suggests an involvement of sex steroids (primarily testosterone [T] and estrogen [E]) and a developmental origin that predates puberty and may indeed extend back to the 1st trimester of pregnancy. In 2D:4D, we may have a relatively fixed record...
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