Previous research has established a relationship between prenatal testosterone and sex-linked behavior, such that higher levels of prenatal testosterone are related to more masculine behaviors. Yet, little is known about the postnatal androgen surge, that occur around three-months of age. Preliminary research suggests that higher levels of postnatal testosterone may also result in the masculinization of some sex-typed behaviors (e.g., visual preferences and toy preferences). The primary purpose of this study was to gain a better understanding of the relationship between postnatal testosterone and behaviors in early childhood, including behaviors characteristic of Autism Spectrum Disorders. Sixty-six children, between 4- and 7-years of age, and their parents participated in this study. Saliva samples were obtained and assayed for testosterone levels when children were 3- to 4-months of age. Second to fourth digit ratios were measured and used as indicators of prenatal testosterone exposure. Parents completed one self-report questionnaire (Autism Spectrum Quotient) and several parent-report questionnaires (Autism Spectrum Quotient-Children's Version, Empathy Quotient-Children's Version, Systemizing Quotient-Children's Version, and Child Behavior Checklist), while children participated in various experimental tasks (Expressive One Word Picture Vocabulary Test, Playmate and Play Style Preferences Structured Interview, mental rotation task, two false belief tasks, an emotion recognition task, and an eye-tracking task). Overall, lower digit ratios, indicative of greater prenatal testosterone exposure, were associated with more masculine behaviors. For example, lower digit ratios were predictive of less time required to complete a mental rotation task and were correlated with lower empathy scores, smaller vocabularies, lower emotion recognition scores and less visual interest in viewing the eye portion of faces. A novel finding of this study was that higher postnatal testosterone levels at 3-months of age were predictive of less visual interest in people compared to objects at 5-years of age. This finding supports the idea that the postnatal surge of testosterone that occurs in early infancy could have organizational effects on behavior, especially behaviors required for socialization. However, future research establishing a link between postnatal testosterone and behaviors beyond early childhood is required before establishing this postnatal phase as another critical period for the development of later behaviors.
