2D:4D ratios in the first 2Â years of life: Stability and relation to testosterone exposure and sensitivity

► Ethnicity differences in 2D:4D apparent in first 2 years of life. ► Sex differences in 2D:4D small and inconsistent in first 2 years of life. ► Interaction of neonatal testosterone and receptor sensitivity predicts 2D:4D in males. ► Instability in 2D:4D across age. ► 2D:4D collected in early childhood may not be a reliable proxy for prenatal testosterone.