Language retrogenesis as a window to language evolution

Abstract

Several structurally simplified forms of language (sometimes called, ‘degraded’) have been explored as possible proxies to previous stages in the evolution of language. In this paper, we focus on two of such forms, namely, child language and language in aging. Specifically, we re-examine the hypothesis of language retrogenesis, according to which language loss in aging parallels, though inversely, language acquisition by the child. We present evidence supporting this view, particularly, in the domain of complex aspects of language with high cognitive reliance, including lexical access (demanding the mapping of meanings to phonological representations), the understanding of non-literal meanings (demanding the access to the context and to encyclopedic knowledge), the resolution of lexical competition, and the understanding and production of complex syntactic structures (demanding more working memory resources). We further consider whether these changes recapitulate aspects of language phylogeny in the species. We have also found some support to this view, as the involved areas (like the inferior frontal gyrus), are phylogenetically newer, as shown by interspecies comparison. Finally, we advance a new testing arena for this hypothesis, involving some of the cortico-subcortical circuits controlling both reactive aggression and complex syntax.