What Can Developmental Language Impairment Tell Us about the Genetic Bases of Syntax?

Neuroconstructivist accounts of language acquisition have questioned whether we need to posit innate neural specialization for syntax, arguing that syntactic competence is an emergent property of the developing brain. According to this view, specific syntactic deficits in children are the downstream consequence of perceptual, memory, or motor impairments affecting systems that are implicated in nonlinguistic as well as linguistic processing. Genetic studies of developmental language disorders pose difficulties for this viewpoint; although syntactic deficits are highly heritable, they are not readily explicable in terms of lower-level perceptual or motor impairments, and are distinct from limitations of phonological short-term memory. Data do not support the notion of a single "grammar gene," but rather are compatible with an Adaptationist account, which postulates that humans evolved a number of neural specializations that are implicated in language processing. Cases of heritable language impairment may help us identify what these specializations are, provided we focus attention on those rare disorders that represent departures from normality, rather than the tail end of normal variation.