In this paper, we investigate the relationship between economic and population growth in an endogenous growth model driven by human capital accumulation Because we allow for endogenous population growth, we adopt the population criterion “Relative Critical Level Utilitarianism”, which allows the critical level utility to depend on parents' well-being. In this scenario, we investigate the equilibrium relationship between economic growth and population growth and we provide the conditions for the economic take-off to occur. A simulation analysis calibrated on developing countries shows that the model has the potential to explain the dynamics of the latter variables experienced by those countries