Revisiting the hypothesis of language retrogenesis from an evolutionary perspective.

Abstract

In this article, we reexamine the hypothesis of language retrogenesis, that is, the assumption that language change over healthy ageing mirrors, albeit inversely, language acquisition by the child. We additionally question whether this inverse pattern can as well be observed at the cognitive and neurobiological levels, and whether it can be informative (and a consequence, in fact) of how language evolved in humans. We compare the language strengths and weaknesses signifying language acquisition and its eventual decay in healthy ageing. We further compare age-related cognitive and neurobiological readjustments during each of these two developmental stages, with a focus on brain areas involved in language processing. Finally, we delve into the evolutionary changes experienced by these areas. We present evidence supporting the hypothesis of retrogenesis in two domains of language: the lexicon (lexical access, understanding of nonliteral meanings, and resolution of lexical competition) and syntax (understanding and production of complex sentences). Additionally, we show evidence that the brain areas supporting these complex tasks are late-myelinated in childhood and early-demyelinated during ageing. Finally, we show that some of these areas (such as the inferior frontal gyrus) are phylogenetically newer. Language acquisition in children and language degradation/loss in healthy ageing follow the principle of retrogenesis, but mostly in domains that are cognitively demanding and that depend on recently evolved brain devices. Putting this differently, the components of language that emerged more recently appear to be more, and earlier, affected during ageing, as well as developed later over childhood. (PsycInfo Database Record (c) 2023 APA, all rights reserved).