Physiology and Development: Why the West is Taller than the Rest∗

Abstract. We hypothesize that the timing of the fertility transition is an im-portant determinant of comparative physiological development. In support, we provide a model of long-run growth that elucidates the links between popula-tion size, average body size and income during development. Industrialization is shown to be accompanied by a reduction in family size and an intensifica-tion 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