Compare and contrast three major theoretical approaches to language acquisition: nativist, behaviorist, and social interactionist theories. For each approach, explain its fundamental claims about the mechanisms underlying language learning, the role of innate knowledge versus environmental input, and the relationship between cognitive development and language acquisition. Evaluate the empirical evidence supporting each theory, including cross-linguistic studies, case studies of language deprivation, and research on atypical language development. Discuss how contemporary theories attempt to integrate insights from multiple perspectives.