Two Views of the Sources of Global Divergence: Jared Diamond and Jeffrey Sachs

J. Bradford DeLong

For the plenary session of the Economic History Assocation's annual meeting this year we--that is, the program committee--mostly it was Ken Sokoloff's idea, and a very good idea it was--invited Jared Diamond and Jeffrey Sachs to speak. We thus invited two non-economic historians who have nevertheless done world-class work in economic history, both working on understanding the origins of the extraordinary gaps in wealth and productivity found in today's world.

Jared Diamond spoke first, and largely gave a precis of his superb book, Guns, Germs, and Steel: The Fates of Human Societies, which I love (see

Diamond's book investigates the sources of Eurasian dominance over the past ten centuries of world history. It is a fact that people from Eurasia conquered Peru, Mexico, Ghana, Australia, and most of the rest of the world as well. It is a fact that Incas, Aztecs, Ashanti, or Australians did not conquer Eurasians. It is this that Jared Diamond explains--largely successfully--in this book. And his answer can be summed up in one phrase: "seeds, germs, size, and guns."

  • Eurasian societies acquired a key advantage relative to other societies because of seeds.
  • Eurasian societies acquired a key advantage (relative to other societies) in their resistance to germs.
  • The relatively advantageous biological endowment of Eurasian societies was then reinforced because of the size of Eurasia.
  • And the relative edge possessed by European societies was then amplified to overwhelming proportions by guns.

Begin with seeds. Over the past twelve thousand years agriculture has been invented perhaps nine times around the globe: in New Guinea, in China, in the Middle East, in North America, in Mexico, in the Andes, and in other places as well. But those humans who lived in the Fertile Crescent of the Middle East were lucky. The plants they had available to domesticate were the easiest to tame, grew the fastest, and had the largest seeds. Thus Middle Eastern agriculture--based on wheat and its cousins--had the potential to support higher population densities.

Those who invented agriculture in the Middle East were fortunate in another area. Eurasia had lots of large animals, and lots of large animals--aurochs, boar, ancestral sheep and goats, horses--that could be domesticated. Successful domestication of large animals gave a further boost to Middle Eastern productivity, and allowed still higher population densities. Moreover, living in close proximity to animals gave Eurasians both the epidemic diseases that were to devastate the populations of the Americas, Oceana, and Australia when contact came, and the resistance to those diseases.

Technologies invented in the Middle East (and elsewhere in Asia) then diffused over the entire great continent. Moving east or west from the Middle East one encounters roughly similar climates for long distances. Thus a pattern of agricultural technology that was good and productive in the Indus Valley had a good chance of also being useful in (say) Spain. The size of Eurasia meant that there were many different groups of people who could invent new technologies. The long east-west axis of Eurasia meant that invented technologies could then diffuse.

By contrast, technologies invented elsewhere had a difficult time diffusing across oceans, or through ecological barriers within which technologies ceased to be of use. Corn took several thousand years to diffuse from Mexico north across the desert to the Mississippi Valley, in large part because corn selectively-bred for Mexico germinates too early and takes too long to grow for it to be of any use in Missouri. The llama never made it north from the Andes to the Valley of Mexico. The inhabitants of New Guinea and of Australia were on their own, able to draw only on the technologies they could invent by themselves. Because their population was low, and because one head is worse than two, the rate of growth of their technology was slow. Thus Eurasians were perhaps 4000 years "ahead" of the inhabitants of other continents in the development of technologies like agriculture, pottery, metalworking, state organization, and so forth--technologies that would prove to be the key foundations on which everything else is built.

Africa as well found itself largely on its own as far as technological development was concerned. Middle Eastern agriculture did very well on the north coast of Africa, but could not diffuse across the Sahara desert--and would have been of little use had it done so, for temperate agriculture does not flourish near the equator. (the failure of Indian Ocean traders to carry Eurasian agriculture to the highlands of Kenya and the grasslands of South Africa remains a mystery.)

The better agriculture of Eurasia gave it higher population densities. The enormous size and high population densities of Eurasia gave it the overwhelming bulk of world population. The large population share meant that Eurasia generated the lion's share of inventions and innovations. The ease of communication and diffusion across Eurasia meant that inventions in one part spread within centuries to other parts: China could not long retain the silkworm for itself, nor could India long retain the zero. Thus a positive-feedback process increased Eurasia's edge. Faster and widely-diffused technological progress gave Eurasians the wheel, sophisticated textiles, advanced metalworking, shipbuilding, the state--and the gun.

Thus when 1492 came Eurasian cultures had extraordinary advantages over others: decimated by diseases against which they had no resistance, out-organized, and without guns, other cultures found themselves conquered and dominated by those who came to their lands to serve the king, to serve God, to win glory, and to get rich.

But why Europe? Why did the subcontinent at the western edge of Eurasia acquire so much dominance over the rest of Eurasia. Many key inventions--the compass, gunpowder, block printing, and the zero--came to Europe from the rest of Eurasia. So why did small numbers of Europeans conquer large chunks of the rest of Eurasia in the period from 1500 to 1900?

Diamond's answer is that, within Eurasia, Europe had "optimal fragmentation." He runs through the story of China's abandonment of its own pre-Columbian program of large-scale intercontinental oceanic exploration under the Ming dynasty ( because China was centralized, one political decision could cripple a whole line of technological development subcontinent-wide. By contrast, Europe had a unified culture and divided political sovereignty and economic customs. Fragmentation meant that different modes of social organization and technological development could be tried in Europe. Cultural unity meant that successful experiments in social organization and technological development would then be observed elsewhere in Europe. And they would quickly and rapidly be copied. A more fragmented subcontinent than Europe would have seen many innovations which would never have spread--as in India, where the caste system blocked communication (it's hard to learn from people if you are polluted by their presence). A more unified subcontinent would generate a much smaller number of innovations--as in China.

But this argument for European dominance within Eurasia is not yet fully developed: it is more a placeholder than an explanation.

Jeffrey Sachs then gave a talk I had not heard before. He was eloquent--the best I have ever heard him give, and I have heard him talk 30 or so times, all of which have been high-quality talks.

Sachs began by praising his predecessor: saying that Guns, Germs, and Steel was a wonderful book that had taught him many important lessons. The most important lesson he learned, said Sachs, is that a large chunk of technology is ecologically specific, and that as a result technological diffusion is amazingly slow when it must take place across an ecological divide. This was true in the past, as pre-Columbian Mexican technology failed to diffuse north across the ecological divides to what is now the United States or as Middle Eastern technology failed to diffuse south across the ecological divides to east Africa. And this is true in the present, as technology fails to diffuse from the globes temperate zones to the globe's tropics.

This lesson, said Sachs, is one key to understanding the causes of the savage inequalities that exist in the world today between the temperate--not the "North" because the far south of Australia, New Zealand, Argentina, Chile, and South Africa are temperate and rich as well--and the tropical. The tropics begin with a substantial disadvantage in agricultural productivity and public health. This initial disadvantage is then amplified because the richer temperate zone generates more new technology--technology that is then of little use in the tropics. The difficulty of technology diffusion across ecological divides combines with other positive-feedback effects to widen what was once a small difference between temperate and tropic into today's enormous difference.

Ecology matters a lot for reasons that are both intrinsic and the result of dynamic social processes. The three key questions to ask of any region are: Is it able to trade with the rest of the world--on the ocean or on an ocean-navigable river? Does its soil trap nutrients to make agriculture productive? Does its climate kill diseases, or are diseases and parasites endemic?

Thus what turns out to be really important, said Sachs, is whether there is a winter with freezes. A winter with freezes leads to a much more nutrient-rich soil and also kills many parasites and diseases. Malaria is just not an issue where there is a winter.

Warm, tropical year-round temperatures are very tough on food production:

  • Grain, tuber, and pulse output lower in warmer climates.
  • Rain leaching of nutrients.
  • No winter during which the soil is held in place while plant matter continues to break down.
  • Pests and parasites.
  • Tropical plant respiration eats up a lot of photosynthesis.
  • Heat means evaporation means that water availability is low even where rainfall is high.

And warm, tropical temperatures are very tough on public health:

  • Vector-borne diseases hugely favored by warm temperatures.
  • Water-borne diseases also favored by warm temperature.
  • Catastrophic effects of endemic malaria.

Also important is trade: 52% of world GDP is produced on the 8% of habitable land within 100 km of the coast or a sea-navigable river.

Now just because you're in the temperate zone doesn't mean you'll be rich, Sachs said. Consider China: late-Ming and Ch'ing dynasty stagnation, followed by the Opium Wars, and then one demaned horrible thing after another for 150 years until 1978, when things start to turn around. Now, said Sachs, China is on track to rapidly develop, because it doesn't have either the horrible disease environment or the agriculturally-unproductive soil of the tropics.

But if you are in the tropics and are far from ocean transport, you are in big trouble.

How has the tropical initial disadvantage amplified itself over the past two centuries? Five sets of factors at work:

  • Technology in critical areas like health and agriculture (but also construction and some segments of manufacturing) is, Sachs said, surprisingly ecologically specific.
  • By the start of modern economic growth temperate-zone technologies were more productive than tropical-zone technologies.
  • Technological innovation is an increasing returns to scale activity (thus what were moderate differences 200 years ago have exploded since).
  • Societal dynamics--urbanization and demographic transition--are two further amplifiers of the process (economies with high disease burdens are also, ironically, economies with highest rates of population growth because the demographic transition to zero population growth requires low infant mortality as a trigger).
  • And then, Sachs said, there are the geopolitical factors: imperialism, and rich country control of international institutions. Bad advice from the IMF and the World Bank.

How does the future look? Bleak, Sachs said. The temperate zones could do a lot of things to help the tropics--for a cost of pennies on the scale of their resources. But they won't: the political will is not there. Research and development will continue to be focused on producing technologies that work very well indeed in the temperate zones, but badly if at all in the tropics. AIDS will devastate Africa and chunks of South Asia. Continued high population growth will lead to continued substantial damage to the ecology and thus the agriculture of regions where 70% of the people are still farmers. Today's savage inequalities between nations will continue to grow.

I was extremely impressed by both Diamond and Sachs. I learned relatively little from Diamond's talk, but that was only because I had closely and assiduously studied Diamond's books over the past several years. I learned much more from Sachs's talk: it pulled together a number of factors that I had considered in isolation, but that I had not considered together. It put pieces I knew together in a new way, and they looked like they might well fit properly.

Nevertheless, I thought Sach--while eloquent, persuasive, and largely right--was a little too enthusiastically taking on the role of Jeremiah. It seemed to me that he could have with equal justice (although not with more justice) have given the same talk with a much more positive conclusion. He could have said that:

  • The tropics are now well advanced in their demographic transitions to zero population growth. Estimates of future world population growth have been falling for more than a decade. It is true that for the past century demography has been a powerful amplifier of inequality--that the poorest and sickest countries have had the fastest population growth rates, and thus the fastest rates of ecological degradation and the slowest rates of growth in capital intensity. But this won't be true in the future. And this will greatly ease the task of tropical development.
  • That even though tropical agriculture will remain (for ecological reasons) relatively unproductive compared to temperate agriculture, tropical urbanization is now far enough advanced that agricultural productivity is no longer the factor determining national wealth. The tropics' comparative advantage is now and in the future will be greater in light manufacturing: in a generation the tropics will import food on a large scale from the temperate zone. The fact that tropical agriculture has deficiencies will not be very relevant. The key will be productivity in manufacturing and services, where the tropics do not have any ecological disadvantage.
  • A lot more can be done for tropical public health, and it can be done very cheaply indeed in terms of the production of the industrial core.
  • That we now know much more about development than we used to. We are no longer advising India to copy the British Labour Party of Clement Attlee. We now know how to do "industrial policy"--that the keys are to make sure that imports of capital goods are cheap, that firms successful in exporting to the world market are not penalized, and that--because people are myopic--that relative price structure for a country today should reflect not its current pattern of comparative advantage but what its pattern of comparative advantage will be in a generation.
  • And Sachs could have finished by saying that we now live in One World: that in the long run the fact that people can communicate so cheaply and quickly will mean that voters in Tennessee will know about and care about people dying of malaria in the Ganges Valley. Thus even though the political will for effective temperate action to make the tropical development path easier does not exist today, it will exist in the future.

The message would then have been very different: it would have been that the Age of Jeremiah was about to end, and that even though in the past the tropics had had massive ecological disadvantages that then had been greatly amplified by socio-economic processes, that that past was not a good guide to what to expect in the future.

It was at the end of America's Constitutional Convention that Benjamin Franklin stood, and said that for the entire Convention he had been looking at the picture on the wall and wondering whether it was of a sunrise or a sunset. But, Franklin said, now that the Convention had finished its work and he had digested the plan proposed, he knew the answer: that it was a rising, and not a setting sun.

Raw notes from Claudia Goldin's EHA
presidential address: "The Human Capital
Century and American Leadership: Virtues
of the Past"

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