Sir

Stephen G. Warren and Roger Short leave the reader puzzled about how the volume of agricultural output sets limits to the size and growth of human population (Nature 397, 101; 1999). Both authors agree with Malthus that such limit-setting occurs, but Short shows that it does not operate through hunger reducing women's fertility. But surely famine and malnutrition sharply increase child mortality, thereby reducing recruitment to the ranks of sexually mature women and so rendering population growth impossible.

The increase in food production began in Europe in the seventeenth and eighteenth centuries and, at least initially, owed more to better organization than to science.