Physiology and Development: Why the West is Taller Than the Rest

We hypothesise that the timing of the fertility transition is an important determinant of comparative physiological development. In support, we provide a model of long‐run growth that elucidates the links between population size, average body size and income during development. Industrialisation is shown to be accompanied by a reduction in family size and an intensification of nutrition per child. Early transition countries are therefore expected to be more developed today, economically and physiologically. Empirically, the timing of the fertility transition is strongly correlated with average body size across countries.