Abstract: The authors’ analysis of growth assumes endogenous fertility and a rising rate of return on human capital as the stock of human capital increases. When human capital is abundant, rates of return on human capital investments are high relative to rates of return on children, whereas, when human capital is scarce, rates of return on human capital are low relative to those on children. As a result, societies with limited human capital choose large families and invest little in each member; those with abundant human capital do the opposite. This leads to two stable steady states. One has large families and little human capital; the other has small families and perhaps growing human and physical capital. Copyright 1990 by University of Chicago Press.