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 (Fouquet
et al.
2016
R. 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 in
F
0
are already present in the cries of pre-verbal babies. While based on a small sample (
n
= 15), our results indicate that the
F
0
of babies' cries at 4 months of age may predict the
F
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 with
F
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 originate
in utero
and thus already be present soon after birth.
Jan Willem De Lind van Wijngaarden, Male Homosexuality in 21st-Century Thailand : A Longitudinal Study of Young Rural, Same-Sex-Attracted Men Coming of Age