Fertility in an Unequal, Innovative World

We develop a theory of the income–fertility relationship across all stages of development. Technological progress shapes fertility through two opposing channels: it raises the return to education, reducing desired family size, and it generates inequality which, depending on the development stage, can raise aggregate fertility. Their interaction produces a non-monotonic historical fertility path — rising in the Malthusian regime, falling during the demographic transition, and rising again at high income. A key implication is that inequality reshapes the composition of fertility across the human-capital distribution, changing the sign of the link between technological progress and long-run growth in a regime-dependent way. We provide empirical evidence consistent with the mechanism using US state-level data. Depending on how technological progress and inequality interact, the economy may achieve sustained growth, an Empty Planet, or Malthusian-like stagnation.