Geography & disease environment

Thesis

The Great Divergence can be traced all the way back to the accidents of geography that set the initial conditions for Eurasian civilization. Eurasia’s east-west axis allowed crops, livestock, and technologies to diffuse rapidly across similar latitudes; Africa’s and the Americas’ north-south axes did not. Eurasia had the lion’s share of domesticable animals and cereal crops; other continents had far fewer. Within Eurasia, Europe was further advantaged by a peninsular, heavily indented coastline producing multiple defensible polities (hence fragmentation); by navigable interior rivers facilitating trade; by temperate climate; by diverse microclimates within short distances; and — crucially for the Columbian exchange — by the accident of being west-facing on a continent whose western ocean led to the Americas.

Disease environment then compounded the geographic advantage in two directions: Europeans’ long co-evolution with livestock-origin diseases gave them partial immunity that devastated Amerindian populations on contact (enabling conquest and settler colonies); and Europe’s temperate-zone disease burden was lower than the tropical-zone burdens faced by South and Southeast Asian populations, giving European adults more working years of healthy productivity. Jeffrey Sachs and others have argued that this temperate-tropical disease-burden differential persists into the modern era and explains a substantial share of contemporary cross-country income differences.

The Jared Diamond strong-form version: the Great Divergence was essentially determined by 8000 BCE, when the agricultural revolution began on the Fertile Crescent’s peculiarly rich combination of domesticable crops and animals; everything since is elaboration on a geographic head start.

Lead proponents

Jared Diamond — Guns, Germs, and Steel (1997) is the canonical popular-science argument for biogeographic determinism of civilizational outcomes. Diamond is a biogeographer, not an economic historian, and his argument reaches from 10,000 BCE to the present.
Jeffrey Sachs — development economist at Columbia; a long series of papers (including the Sachs-Gallup-Mellinger 2001 work on climate and development) has argued that geography and especially disease environment explain significant cross-country variation in long-run growth, even after controlling for institutions.
Alfred Crosby — Ecological Imperialism (1986) provides the ecological-history backbone: European biotic exports (crops, livestock, weeds, pathogens) systematically out-competed native species in temperate-zone settler colonies, transforming the Americas and Australasia into “Neo-Europes.”
William McNeill — Plagues and Peoples (1976) is the foundational demographic-disease argument; Europe’s endemic disease pool gave its populations advantages in New World conquest and partial advantages in Old World contact.

Key arguments

Eurasia had a biogeographic head start over other continents. Of the world’s large mammals suitable for domestication, most were Eurasian. Of the world’s major cereal crops, most were Eurasian. The east-west axis allowed these to diffuse along similar latitudes in a way the Americas’ and Africa’s north-south axes did not. By 1500, Eurasian civilizations had a 3,000+ year head start in agricultural productivity, sedentary population density, and technological accumulation.
Within Eurasia, Europe’s fragmentation was geographic. Diamond’s argument about why Europe and not China: Europe’s coastline is deeply indented (Iberia, Italy, Greece, Jutland, the British Isles, Scandinavia), producing natural defensible zones that sustained independent polities. China’s geography (a single coastline, two great rivers joining a contiguous plain) facilitates unification. The state-competition/fragmentation position is, in this framing, downstream of geography.
Navigable rivers and coastal waters reduced transport costs. The Rhine, Danube, Thames, Seine, and extensive European canal systems made internal trade cheap. China’s Grand Canal was spectacular but a single engineered artery; Europe’s natural river network was more extensive in proportion to territory.
Disease-environment differentials favored temperate Europe. Tropical disease burdens (malaria, schistosomiasis, hookworm, yellow fever) reduce working-age productivity. Temperate Europe escaped the worst of this. In the modern era, Sachs and colleagues have shown cross-country development correlates robustly with tropical-zone status even controlling for other variables.
The Columbian Exchange was one-sided because of differential disease exposure. European populations had (partially) adapted to livestock-origin diseases (smallpox, measles, influenza variants) over millennia; Amerindian populations had no equivalent exposure. The result: 50–90% mortality in contact-era Amerindian populations, enabling the settler-colonial transformation of the Americas that fed the European “ghost acres” advantage. If Amerindians had had European-equivalent livestock and disease history, the Columbian Exchange would have been far more symmetrical.
Modern institutional differences partly track geographic ones. The Acemoglu-Johnson-Robinson “reversal of fortune” paper is ambiguous on causal direction: yes, institutions were transplanted differently to different colonial environments, but which institutions got transplanted where was determined by geography — specifically by settler-mortality disease environments. This makes institutions a proximate cause whose deep cause is geography.

Key evidence

Domesticable-animal counts by continent. ~14 large domesticable mammals globally, of which ~13 are Eurasian. This asymmetry is real and consequential for pre-industrial productivity.
Sachs-Gallup-Mellinger tropical-zone regressions — cross-country contemporary income correlates strongly with distance from the equator and with tropical-disease exposure, even after controlling for institutions.
Historical demography of contact-era America — population collapses documented across Central Mexico, the Andes, the Caribbean, and North America post-1492 are quantitatively enormous.
Crosby’s ecological-imperialism documentation — the systematic displacement of native biota in temperate settler colonies by European crops, weeds, livestock, and pathogens.
Sachs et al. on malaria and economic development — contemporary and historical evidence that endemic malaria cuts national GDP growth by ~1 percentage point per year; the accumulated effect over centuries is substantial.
River and coastline geometric measures — Europe’s coastline-to-landmass ratio is ~4× China’s; navigable-river kilometers per unit area similarly favors Europe.

Major critiques

Geography cannot explain timing. Europe’s geographic endowments were largely static from 10,000 BCE through the present. Yet the divergence happened in a specific 300-year window (1500–1800). Geographic determinism can tell us which regions could diverge, but not which ones did or when. Any explanation requires proximate institutional and cultural factors; geography alone is under-specified.
Asia was ahead of Europe in 1500 despite the geographic endowment being the same. If European geography were decisive, Europe should have been ahead throughout recorded history. Instead, Song China, Abbasid Baghdad, and Mughal India all substantially outperformed contemporary Europe in various pre-modern periods. Geography cannot explain the reversal.
From the institutional school: Diamond’s biogeographic determinism is a “geography fallacy” that erases human agency and ignores the variation in institutional quality that actually explains modern economic differences. Settler mortality is a red herring when sub-Saharan Africa and Latin America are both tropical and have very different institutions and outcomes today.
“Europe and China had the same latitude” problem. The Yangzi delta is at roughly the latitude of southern France. The claim that European temperate advantage explains divergence from tropical Asia fails for the most economically relevant Asian comparator (the Yangzi), which was temperate.
The east-west-axis argument is thinner than Diamond makes it. Civilizations in tropical Africa, pre-Columbian America, and Oceania had substantial agricultural and urban development despite north-south axes. The axis-argument explains some of what it needs to, but is stretched as a single-factor theory.
Pomeranz’s ghost acres were human choices, not geographic inevitabilities. Europe had access to the Americas only because European states chose to commit to transatlantic conquest and colonization. Geography enabled the choice; it didn’t force it. The Ming decision to end oceanic exploration shows that an equally-capable Chinese state could have chosen differently. “Geography” collapses here into a political choice.
Within-Europe variation. Geographic endowments are similar across NW Europe, Southern Europe, and Eastern Europe, but economic outcomes diverged sharply starting ~1500. Sub-continental variation is not predicted by geography.
Political-science critiques of Sachs. The Sachs-Gallup-Mellinger regressions have been challenged extensively — contemporary disease burden may be endogenous to institutional quality; controlling for institutions eliminates much of the tropical-zone effect; and the geographic-determinist literature selects on the dependent variable by treating “developed” and “tropical” as binaries rather than continua.

Status

Heterodox, with a contested empirical foothold. Diamond is enormously popular with general readers; most academic economic historians reject his framework as too coarse for the specific Great Divergence question. Sachs-style disease-environment arguments are more empirically respectable but still generally subordinate to institutional arguments in modern development economics. A fair summary: geography is a legitimate background variable that cannot be ignored, but it is rarely treated as a primary cause of the Great Divergence by contemporary scholars. Its most defensible role is in explaining the initial conditions and constraints within which institutional and cultural factors operated.