Abstract
During the first few years of life, girls typically have a larger expressive vocabulary than boys. This sex difference is important since a small vocabulary may predict subsequent language difficulties, which are more prevalent in boys than girls. The masculinizing effects of early androgen exposure on neurobehavioral development are well-documented in nonhuman mammals. The present study conducted the first test of whether early postnatal testosterone concentrations influence sex differences in expressive vocabulary in toddlers. It was found that testosterone measured in saliva samples collected at 1–3 months of age, i.e., during the period called mini-puberty, negatively predicted parent-report expressive vocabulary size at 18–30 months of age in boys and in girls. Testosterone concentrations during mini-puberty also accounted for additional variance in expressive vocabulary after other predictors such as sex, child’s age at vocabulary assessment, and paternal education, were taken into account. Furthermore, testosterone concentrations during mini-puberty mediated the sex difference in expressive vocabulary. These results suggest that testosterone during the early postnatal period contributes to early language development and neurobehavioral sexual differentiation in humans.
Highlights
Certain aspects of language development differ between the sexes
The present study is the first to demonstrate that testosterone during the early postnatal period of mini-puberty predicts the sex-related differences that have been observed in early expressive vocabulary development
Differences were found between boys and girls in salivary testosterone at 1–3 months of age and in expressive vocabulary size at 18–30 months of age
Summary
Certain aspects of language development differ between the sexes. During the first few years of life, girls on average speak more words and have a larger expressive vocabulary than boys (Berglund et al, 2005; Feldman et al, 2000; Fenson et al, 1994; Zubrick et al, 2007). Expressive vocabulary development is important, since a small vocabulary may indicate language delay and predict subsequent language difficulties, which are more prevalent in boys than girls (Hawa and Spanoudis, 2014; Rescorla, 2011). Androgen exposure may contribute to the sex difference in early expressive vocabulary development. The testicular hormone, testosterone, are elevated in male fetuses between about 8 and 24 weeks of gestation (Reyes et al, 1974). There is an early postnatal surge of testosterone in male infants, called “mini-puberty”, with testosterone peaking at about 1–3 months of age, and declining to baseline by about 6
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