Increasing evidence suggests that two learning and memory brain circuits that pre-date humans—declarative memory and procedural memory—have been co-opted (hijacked) to support the learning, representation, and processing of language. From both human and animal studies, these circuits are well-understood at many levels (e.g., computational, developmental, neuroanatomical, endocrine, genetic, and even how learning and retention in the circuits can be enhanced). Thus, this independent knowledge leads to a wide range of specific testable predictions for language that have the potential to substantially advance our understanding of this domain. Converging evidence from psycholinguistic, neurological, neuroimaging, electrophysiological, and endocrine studies are largely consistent with these predictions. The evidence reveals that lexical (word), grammatical (rule), and other language abilities rely on these circuits in specific ways in both first and second language. Newer evidence suggests that other cognitive domains such as reading and math may also depend on the circuits. The research has implications not only for the evolution of language, but also for for how language learning and use can be improved.