| In the first chapter, questions regarding the origins and evolution of language are discussed, along with methods for the investigation of such questions, including studies of fossils, archaeology, living primates, and modern human variation. In Chapter 2, primate communication studies, including laboratory and field studies of perception and call production are discussed; also discussed is the finding that primate (and other nonhuman) call perception is remarkably similar to human language sound perception. Ape language studies, as well as their possible relevance to origins of language and "humanness" are also discussed. In the third chapter, the heritability of language ability and disability is investigated, primarily through twin studies, and the conclusion reached that there is ample evidence for a genetic influence on variation in language ability, although this conclusion is based mainly on work with children. In chapter 4, first and second language acquisition are compared, and found to differ in many ways, but it is not clear whether they differ in some essential way or not. Critical periods for language learning are also discussed; it seems likely that different aspects of language learning occur with greatest facility at different times of life, with phonological skill declining first, well before puberty.;In the final chapters, the twin project is presented and discussed. The second language aptitude of 53 pairs of MZ and DZ twins was investigated using the MLAT (Modern Language Aptitude Test of Carroll and Sapon (1959)), a perception test (of discrimination of minimal contrast pairs), and a production test (of twins' abilities to produce the minimal contrasts). An overall trend toward higher MZ than DZ intraclass correlations was found, but this trend was of statistical significance for the production test alone. There was a negative correlation between age and MLAT3, MLAT5 and production test scores. A questionnaire given to the twins showed high correlations between test scores and such things as foreign language class grades, self assessments of language learning ability, spelling ability and grammatical ability, and musical training and ability. These results and their implications for variation in language ability and its heritability were discussed. |
