The Etiology of Diverse Receptive Language Skills at 12 Years

Purpose: In the 2nd decade of life, language skills expand in both quantitative and qualitative ways. The etiology of these new skills and the relationships among them have been little explored. Method: Taking advantage of widespread access to inexpensive and fast Internet connections in the United Kingdom, we administered four Web-based measures of receptive language development-Vocabulary, Listening Grammar, Figurative Language, and Making Inferences-to a sample of 12-year-old twin pairs (N=4,892) participating in the Twins Early Development Study (TEDS; Oliver & Plomin, 2007). Results: The 4 measures showed moderate phenotypic intercorrelation. All 4 showed moderate genetic influence (a(2) between .25 and .36) and low shared environmental influence (c(2) between .13 and .19). The median genetic correlation among the 4 measures was .87, indicating strong genetic overlap among them. A latent factor score for Language, based on the common variance among the measures, showed substantial genetic influence (a(2) = .59) and moderate shared environmental influence (c(2) = .28). A small but significant sex difference favored females on the Listening Grammar and Making Inferences tests, but there was no evidence for sex differences in the etiology of any of the measures. Conclusion: Despite the emergence of new skills at this developmental period, from the etiological perspective, language skills remain relatively undifferentiated at an etiological level.