Abstract: . . .  psycholinguistics Page 1 PLINX204 PSYCHOLINGUISTICS LANGUAGE ACQUISITION – 2006 - 5 Behavioural (‘population’) genetic evidence (2) Twin, Adoption and Linkage studies Basic reading: Stromswold, 2001 (esp. §§10-15); Plomin & Dale, 2000; Friederici, 2005. 1. Background 99.9% of DNA base pairs are the same for all human beings. So our individual uniqueness is due to that 0.1% (plus environment). Following on from last week’s “change of perspective”, note that language could be 100% genetically determined but everyone could be genetically identical, so in normals, no variance would be attributable to genetics. (Consider number of fingers versus weight or BMI). Need to keep apart normal and pathological development. Alpert syndrome (oligodactyly); Laurence-Moon-Biedl syndrome (polydactyly). In language, normal and abnormal development are both subject to genetic influence, though not necessarily the influence of the same genes. 2. Aggregation Nature versus nurture : Family aggregation studies show that the incidence of language disorders is greater among relatives of people with language impairment (‘probands’) than controls. In seven studies, the incidence of positive family history ranged . . .
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