In the first place I identify this ["the equilibrium of poverty"] with primitive agriculture, and two factors have been at work there. One is, of course, population growth. If you were a poor farmer in India, Pakistan, or in much of Africa, you would want as many sons as possible as your social security. They would keep you out of the hot sun and give you some form of subsistence in your old age. So, you have pressure for population growth that is, itself, the result of the extreme economic insecurity. This is something which hasn't been sufficiently emphasized.