This paper shows that merely the Malthusian mechanism cannot explain the pre-industrial stagnation of living standards. Technological improvement in luxury production, if faster than improvement in subsistence production, would have kept living standards growing. The Malthusian trap is essentially a puzzle of balanced growth between the luxury sector and the subsistence sector. The author argues
... [Show full abstract] that the balanced growth is caused by group selection in the form of biased migration. A tiny bit of bias in migration can suppress a strong tendency of growth. The theory reexplains the Malthusian trap and the prosperity of ancient market economies such as Rome and Song. It also suggests a new perspective on the Industrial Revolution.