Language enables cumulative cultural improvement by transmitting mental models

<p>Human culture is distinguished by the accumulation of increasingly sophisticated knowledge of why things work, much of which cannot be readily recovered from observing successful behavior alone. How such knowledge is transmitted across generations remains poorly understood. We tested whether cumulative improvement depends on how knowledge is shared using a decision-making task governed by a hidden relational structure that could not be reliably inferred from observed behavior. Across ten sequential generations (N = 2,000), participants solved the task after either observing a previous participant's behavior or receiving their written advice. Observation produced no cumulative gains, whereas language yielded sustained intergenerational improvements in performance and task knowledge. Messages were progressively refined, increasingly communicating the hidden task structure while filtering incorrect and task-irrelevant content. These findings suggest that language may support cumulative culture when the mental models underlying successful behavior cannot be readily recovered through observation alone.</p>