Two by two: a twin study of second-language acquisition.

In this report, we provide initial results of the first application of the classic twin design to second-language acquisition. The analysis was conducted on assessments teachers made using United Kingdom National Curriculum standards and included 604 pairs of 14-year-old twins. The results demonstrate substantial heritability (.67) and low influence of shared environment (.13) on this measure of second-language acquisition. The heritability of second-language acquisition at 14 years is comparable to the heritability of the two first-language acquisition measures obtained at 12 and 14 years, respectively, and is higher than heritability estimates previously published for first-language acquisition in early childhood. Multivariate behavior genetic analyses suggest very high, but not complete, overlap of genetic influences on first- and second-language acquisition, and less overlap between shared environmental influences on the two domains.