Prediction of hemispheric asymmetry as measured by handedness from digit length and 2D:4D digit ratio.

Hemispheric asymmetry is widely theorised as having a basis in prenatal androgen levels. However, these theories ignore a second round of asymmetrical changes in the brain, which occur at the same time as post-puberty surges in androgens. Hemispheric asymmetry in adults might therefore be explained in terms of the joint effects of prenatal and post-pubertal androgen levels. Evidence is emerging that the ratio between the length of the second and fourth digits (2D:4D) is related to prenatal androgen exposure, and that digit length is related to post-puberty levels of androgen exposure. In this study, hemispheric asymmetry is measured as handedness, prenatal androgen levels as 2D:4D, and post-puberty androgen levels as digit length. Right-handedness is associated with consistent prenatal and post puberty androgen release whereas left-handedness is associated with mixed levels of androgen release. Age, race, and sex effects were explored but were not significant.