Revisiting Nature and Nurture in Second Language Acquisition: A Comparative Analysis with an Environmental-Input Lens

Abstract

The long-standing debate in second language acquisition (SLA) concerning whether language development is primarily driven by innate linguistic mechanisms or by postnatal experience has gained renewed relevance in contemporary foreign language learning contexts. With the global expansion of second language education, particularly in classroom-based and input-constrained environments, strong claims regarding the sufficiency of innate language ability face increasing empirical and pedagogical challenges. Against this backdrop, the present study conducts a comparative analysis of the roles of innate and acquired factors in SLA from the perspective of environmental input. Rather than treating these factors as isolated determinants, the study evaluates their explanatory strength under a unified analytical framework. Methodologically, the study adopts a qualitative comparative design that integrates a systematic literature review with theory-driven case analysis. Drawing on representative empirical studies and meta-analyses in SLA, three comparative criteria are constructed: explanatory coverage, empirical consistency, and pedagogical intervenability. These criteria are applied to examine how innate factors (such as Universal Grammar and language aptitude) and acquired environmental factors (including comprehensible input, interactive input, and output with feedback) account for observed acquisition patterns across different learning contexts. Case analyses are used not for statistical generalization but to illustrate how specific environmental input conditions activate, constrain, or amplify different factors in actual learning processes. The analysis demonstrates that acquired environmental factors exhibit clear explanatory advantages over innate factors under all three criteria. Environmental input accounts for a substantially larger proportion of variance in developmental sequences, shows more stable and convergent empirical effects across studies, and—most critically—can be directly manipulated through instructional design. By contrast, innate factors function primarily as background constraints or moderators whose effects emerge only under particular input, interaction, and feedback conditions and lack direct pedagogical operability. The findings suggest that while innate capacities delimit the boundaries of language learning, it is acquired environmental input that plays the central and actionable role in shaping second language development. This comparative perspective offers both theoretical clarification and practical implications for second language pedagogy in input-limited instructional contexts.