This paper discusses the issues of modularity, Universal Grammar (UG), and transferability in children’s mother tongue (L1) acquisition and second language (L2) learning. In doing so, this paper discusses nativisms’ modularity hypothesis and its three major characteristics; further, this paper introduces controversies on modularity from sociocultural perspectives and connectionism. By comparing and critically analyzing the different approaches to modularity, UG, and transferability of L1 knowledge to L2 acquisition, this paper emphasizes overcoming the modular account of human language and expanding understanding on L1/L2 acquisition or learning. Finally, this paper discusses the pedagogic implications of language modularity, especially the role of L1 on L2 learning in classroom settings.