The pitch of babies’ cries predicts their voice pitch at age 5

Voice pitch (fundamental frequency,F 0 ) is a key dimension of our voice that varies between sexes after puberty, and also among individuals of the same sex both before and after puberty. While a recent longitudinal study indicates that inter-individual differences in voice pitch remain stable in men during adulthood and may even be determined before puberty (Fouquetet al. 2016R. Soc. open sci. 3 , 160395. (doi:10.1098/rsos.160395 )), whether these differences emerge in infancy remains unknown. Here, using a longitudinal study design, we investigate the hypothesis that inter-individual differences inF 0 are already present in the cries of pre-verbal babies. While based on a small sample (n = 15), our results indicate that theF 0 of babies' cries at 4 months of age may predict theF 0 of their speech utterances at 5 years of age, explaining 41% of the inter-individual variance in voice pitch at that age in our sample. We also found that the right-hand ratio of the length of their index to ring finger (2D : 4D digit ratio), which has been proposed to constitute an index of prenatal testosterone exposure, was positively correlated withF 0 at both 4 months and 5 years of age. These findings suggest that a substantial proportion of between-individual differences in voice pitch, which convey important biosocial information about speakers, may partly originatein utero and thus already be present soon after birth.