Population and economic growth under different growth engines

Using a growth model with physical capital accumulation, human capital investment and horizontal R&D activity, this paper proposes an alternative channel through which an increase in the population growth rate may yield a non-uniform (i.e., a positive, negative, or neutral) impact on the long-run growth rate of per-capita GDP, as available empirical evidence seems mostly to suggest. The proposed mechanism relies on the nature of the process of economic growth (whether it is fully or semi-endogenous), and the peculiar engine(s) driving economic growth (human capital investment, R&D activity, or both). The model also explains why in the long term the association between population growth and productivity growth may ultimately be negative when R&D is an engine of economic growth.