R&D-based growth models with human capital accumulation reach a conclusion that long-run growth is unaffected by research activities and government policies and is only driven by preferences and human capital accumulation technology. Zeng (2003) shows that these results only hold when human capital is the unique input in its own production. This paper re-examines Zeng’s findings by introducing several modifications. First, it focuses on only vertical innovation. Second, it argues that human capital is more important than final output in terms of producing research outcome and, hence, replaces final output with human capita in the research equation. Third, it suggests an alternative human capital accumulation specification where knowledge le...