Genetic and Environmental Links Between Natural Language Use and Cognitive Ability in Toddlers.

Although the phenotypic correlation between language and nonverbal cognitive ability is well-documented, studies examining the etiology of the covariance between these abilities are scant, particularly in very young children. The goal of this study was to address this gap in the literature by examining the genetic and environmental links between language use, assessed through conversational language samples, and nonverbal cognition in a sample of 3-year-old twins (N = 281 pairs). Significant genetic and nonshared environmental influences were found for nonverbal cognitive ability and language measures, including mean length of utterance and number of different words, as well as significant genetic covariance between cognitive ability and both language measures.