Interactive Repair in Homesign Reveals the Theory-of-Mind Abilities that May Well Have Driven Language Evolution

It is widely agreed that human linguistic communication draws on theory-of-mind abilities more sophisticated than those possessed by our great ape relatives. However, controversy persists regarding the role of enhanced theory-of-mind abilities in explaining the ultimate origins of language. On one common view, an upgrade in our theory-of-mind abilities was a crucial driver of the expansion of communicative complexity in our line, ultimately culminating in the first human (proto)languages. In contrast, on a rival and increasingly influential view, the enhanced theory-of-mind abilities of humans are instead understood to be a cultural evolutionary product of the appearance of human (proto)languages, with these theory-of-mind abilities feeding back to subsequently affect the shape (e.g., the flexibility) of human linguistic communication. This article aims to progress this debate, and ultimately bridge this divide. Towards this end, we make use of recent empirical work on interactive repair in homesigners (i.e., individuals who lack meaningful exposure to natural language models, but whose developmental environment is otherwise normal). Against the strongest versions of cultural evolutionary thinking in this area, we argue that the way in which homesigners flexibly request repair from conversational partners reveals the possession of theory-of-mind abilities that are distinctively human in their sophistication. Nevertheless, we see reason for positing a residual theory-of-mind gap between homesigners and individuals with normal language exposure, and suggest that this gap may be naturally filled by the linguistic tools and processes emphasized by cultural evolutionary theorists, thereby offering a synthesis of the two schools of thought.