This paper analyzes how the decisions of individuals to have children and acquire skills affect longtermgrowth. We investigatea model in which technical progress, human capital, and population arise endogenously. In such an economy, the presence ofdistortions (such as monopolistic competition, knowledge spillover, and duplication effects) leads the decentralized longrun growth to be either insufficient or excessive. We show that this result depends on the relative contribution of population and human capital in the determination of longterm growth, i. e., on how the distortions affect the tradeoff between the quantity ofoffsprings and the quality of the family members.