Purpose-The present study examined the extent of genetic and environmental influences on individual differences in children's conversational language use.Method-Behavioral genetic analyses focused on conversational measures and 2 standardized tests from 380 twins (M = 7.13 years) during the 2nd year of the Western Reserve Reading Project (S. A. Petrill, K. Deater-Deckard, L. A. Thompson, L. S. DeThorne, & C. . Multivariate analyses using latent factors were conducted to examine the extent of genetic overlap and specificity between conversational and formalized language.Results-Multivariate analyses revealed a heritability of .70 for the conversational language factor and .45 for the formal language factor, with a significant genetic correlation of .37 between the two factors. Specific genetic effects were also significant for the conversational factor.Conclusions-The current study indicated that over half of the variance in children's conversational language skills can be accounted for by genetic effects with no evidence of significant shared environmental influence. This finding casts an alternative lens on past studies that have attributed differences in children's spontaneous language use to differences in environmental language exposure. In addition, multivariate results generally support the context-dependent construction of language knowledge, as suggested by the theory of activity and situated cognition (J. S. Brown, A. Collins, & P. Duguid, 1989; T. A. Ukrainetz, 1998), but also indicate some degree of overlap between language use in conversational and formalized assessment contexts.
Keywordsexpressive language assessment; elementary school pupils; language Contact author: Laura S. DeThorne, University of Illinois at Urbana-Champaign, 901 South Sixth Street, Champaign, IL 61820. E-mail: lauras@uiuc.edu.
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NIH-PA Author ManuscriptA number of twin studies have used quantitative genetic methods to estimate environmental and genetic influences on language development. The twin design hinges on a comparison of monozygotic (MZ) and dizygotic (DZ) twins. Because MZ twins share 100% of their segregating genes and DZ twins share on average 50%, higher similarity between MZ twins is indicative of genetic effects (Plomin, DeFries, McClearn, & McGuffin, 2001). One means of measuring twin similarity is by comparing intraclass correlations for MZ versus DZ twins. The larger the MZ intraclass correlation in comparison with the DZs, the higher heritability (h 2 ) will be. In contrast, shared environmental effects (c 2 ) lead to similarity across all twins. Consequently, similar intraclass correlations between MZ and DZ twins are indicative of shared environmental effects. Finally, the extent to which MZ twins appear dissimilar is attributed to a combination of nonshared environment and error (e 2 ). Nonshared environmental influences are unique to the individual.An underlying assumption of twin methodology is that the nature of genetic and environ...