Language and Biological Adaptation 1 Classification: Social Sciences (Psychology); Biological Sciences (Evolution) Restrictions on Biological Adaptation in Language Evolution

Language acquisition and processing are governed by genetic constraints. A crucial unresolved question is how far these genetic constraints have co-evolved with language, perhaps resulting in a highly specialized, and species-specific language “module”; and how far language acquisition and processing redeploy pre-existing cognitive machinery. Here, we aim to understand the circumstances under which genes encoding languagespecific properties could co-evolve with language itself. We present a theoretical model, implemented in computer simulations, of key aspects of the interaction of genes and language. Our results show that genes for language could only have co-evolved with highly stable aspects of the linguistic environment: a fast changing linguistic environment does not provide a stable target for natural selection. Hence, a biological endowment cannot co-evolve with properties of language that began as learned cultural conventions, because cultural conventions change much more rapidly than genes. We argue that this rules out the possibility that arbitrary properties of language, including abstract syntactic principles governing phrase structure, case marking, and agreement, have been built into a “language module” by natural selection. The genetic basis of human language acquisition and processing did not co-evolve with language, but primarily pre-dates the emergence of language. As suggested by Darwin, the fit between language and its underlying mechanisms arose because language has evolved to fit the human brain, rather than the reverse. Language and Biological Adaptation 3