New research published today in Science is a first-of-its-kind step toward a unified theory of the lexicon and the mind examined across timescales. Cognitive and computer scientists at the University of Toronto, Universitat Pompeu Fabra and the Catalan Institution for Research and Advanced Studies have found child language development and the historical evolution of the world’s languages share a common cognitive foundation—a core knowledge base where patterns of children’s language innovation can predict patterns of language evolution, and vice versa. The result may also help predict how a word’s meaning may change in the future—across different languages, in language learners and in machine learning.