Brad De Long over at his website:
Let me back up and quickly sketch the argument that manufacturing matters, and manufacturing exports matter a lot for industrialization and economic development in the Global South. And let me make the argument in what I regard as the proper way–that is, dropping far back in time and running through the economic history…
I do not, all thing considered, think that, absent the luck and randomness that gave us the British Industrial Revolution, a permanent or semi-permanent “Gunpowder Empires”scenario was the third-millennium likely historical destiny of the Sociable Language-Using Tool-Making Big-Brained East African Plains Ape.
However, this does not mean that the historical destiny looking forward from 1750 or so in the Global South was bright. World population had quintupled in the 2000 years to 1750, carrying with it a notional five-fold shrinkage in average farm sizes, or at least in the amount of land supporting the typical family. The slow pace of technological progress from -250 to 1750 had made up for–indeed, had caused–this rise in population. And the biotechnologies of agriculture were indeed mighty: to 1750 we have the creation and diffusion of maize, of double-crop wet rice, of the combination of the iron axe and the moldboard plow that could turn northern temperate forests into farms, of domesticated cotton, of the merino sheep, and of the potato.
But a human population growing at 10% per generation required more such innovations, lest living standards fall in order to curb population growth via children so malnourished to have compromised immune systems, women who were too thin to ovulate, or increased female infanticide. People in 1750 were as well fed and clothed as they had been in -250. But what would have been the next agricultural miracles? You would have needed a number of them to attain continued total factor productivity growth at 0.02%/year to compensate for the further quartering of farm sizes that would have been inevitable for population growth to continue and human numbers topped 3 billion by 2050. Draft animals are not that much help in a densely populated near-subsistence society: they have large appetites, and the land their foodstuffs grow on is subtracted from that available for people. Only a relatively rich society can afford to replace human backs and thighs with those of horses and oxen.
More here.