How can students of human history profit from the experience of scientists in other historical sciences? A methodology that has proved useful involves the comparative method and so-called natural experiments. While neither astronomers studying galaxy formation nor human historians can manipulate their systems in controlled laboratory experiments, they both can take advantage of natural experiments, by comparing systems differing in the presence or absence (or in the strong or weak effect) of some putative causative factor. For example, epidemiologists, forbidden to feed large amounts of salt to people experimentally, have still been able to identify effects of high salt intake by comparing groups of humans who already differ greatly in their salt intake; and cultural anthropologists, unable to provide human groups experimentally with varying resource abundances for many centuries, still study long-term effects of resource abundance on human societies by comparing recent Polynesian populations living on islands differing naturally in resource abundance. The student of human history can draw on many more natural experiments than just comparisons among the five inhabited continents. Comparisons can also utilize large islands that have developed complex societies in a considerable degree of isolation (such as Japan, Madagascar, Native American Hispaniola, New Guinea, Hawaii, and many others), as well as societies on hundreds of smaller islands and regional societies within each of the continents.
Natural experiments in any field, whether in ecology or human history, are inherently open to potential methodological criticisms. Those include confounding effects of natural variation in additional variables besides the one of interest, as well as problems in inferring chains of causation from observed correlations between variables. Such methodological problems have been discussed in great detail for some of the historical sciences. In particular, epidemiology, the science of drawing inferences about human diseases by comparing groups of people (often by retrospective historical studies), has for a long time successfully employed formalized procedures for dealing with problems similar to those facing historians of human societies. Ecologists have also devoted much attention to the problems of natural experiments, a methodology to which they must resort in many cases where direct experimental interventions to manipulate relevant ecological variables would be immoral, illegal, or impossible. Evolutionary biologists have recently been developing ever more sophisticated methods for drawing conclusions from comparisons of different plants and animals of known evolutionary histories.
In short, I acknowledge that it is much more difficult to understand human history than to understand problems in fields of science where history is unimportant and where fewer individual variables operate. Nevertheless, successful methodologies for analyzing historical problems have been worked out in several fields. As a result, the histories of dinosaurs, nebulas, and glaciers are generally acknowledged to belong to fields of science rather than to the humanities. But introspection gives us far more insight into the ways of other humans than into those of dinosaurs. I am thus optimistic that historical studies of human societies can be pursued as scientifically as studies of dinosaurs—and with profit to our own society today, by teaching us what shaped the modern world, and what might shape our future.
2003 AFTERWORD: Guns, Germs, and Steel Today
GUNS, GERMS, AND STEEL (GGS) IS ABOUT WHY THE RISE OF complex human societies unfolded differently on different continents over the last 13,000 years. I finished revising the manuscript in 1996, and it was published in 1997. Since then, I have been involved mostly in work on other projects, especially on my next book about collapses of societies. Hence seven years’ distance in time and focus now separates me from GGS’s writing. How does the book look in retrospect, and what has happened to change or extend its conclusions since its publication? To my admittedly biased eye, the book’s central message has survived well, and the most interesting developments since its publication have involved four extensions of the story to the modern world and to recent history.
My main conclusion was that societies developed differently on different continents because of differences in continental environments, not in human biology. Advanced technology, centralized political organization, and other features of complex societies could emerge only in dense sedentary populations capable of accumulating food surpluses—populations that depended for their food on the rise of agriculture that began around 8,500 B.C. But the domesticable wild plant and animal species essential for that rise of agriculture were distributed very unevenly over the continents. The most valuable domesticable wild species were concentrated in only nine small areas of the globe, which thus became the earliest homelands of agriculture. The original inhabitants of those homelands thereby gained a head start toward developing guns, germs, and steel. The languages and genes of those homeland inhabitants, as well as their livestock, crops, technologies, and writing systems, became dominant in the ancient and modern world.
Discoveries in the last half-dozen years, by archaeologists, geneticists, linguists, and other specialists, have enriched our understanding of this story, without changing its main outlines. Let me mention three examples. One of the biggest gaps in GGS’s geographic coverage involved Japan, about whose prehistory I had little to say in 1996. Recent genetic evidence now suggests that the modern Japanese people are the product of an agricultural expansion similar to others discussed in GGS: an expansion of Korean farmers, beginning around 400 B.C., into southwestern Japan and then advancing northeast up the Japanese archipelago. The immigrants brought intensive rice agriculture and metal tools, and they mixed with the original Japanese population (related to the modern Ainu) to produce the modern Japanese, much as expanding Fertile Crescent farmers mixed with Europe’s original hunter/gatherer population to produce modern Europeans.
As another example, archaeologists originally assumed that Mexican corn, beans, and squashes reached the southeastern United States by the most direct route via northeastern Mexico and eastern Texas. But it is now becoming clear that this route was too dry for farming; those crops instead took a longer route, spreading from Mexico into the southwestern United States to trigger the rise of Anasazi societies there, and then spreading east from New Mexico and Colorado through river valleys of the Great Plains into the southeastern United States.
As a final example, in Chapter 10 I contrasted the frequency of repeated independent domestications and slow spreads of the same or related plants along the Americas’ north/south axis with the predominantly single domestications and rapid east/west spreads of Eurasian crops. Even more examples of those two contrasting patterns have continued to turn up, but it now appears that most or all of Eurasia’s Big Five domestic mammals also underwent repeated independent domestications in different parts of Eurasia—unlike Eurasia’s plants, but like the Americas’ plants.
These and other discoveries add details, which continue to fascinate me, to our understanding of how agriculture’s rise triggered the rise of agriculturally based complex societies in the ancient world. However, the biggest advances building on GGS have involved extensions into areas that were not the book’s main focus. Since publication, thousands of people have written, phoned, e-mailed, or buttonholed me to tell me of parallels or contrasts that they noticed between the ancient continental processes of GGS and the modern or recent processes that they study. I’ll tell you about four of these revelations: briefly, the illuminating example of New Zealand’s Musket Wars; the perennial question “Why Europe, not China?” in more detail, parallels between competition in the ancient world and in the modern business world; and GGS’s relevance to why some societies today are rich while others are poor.
IN 1996 I DEVOTED one brief paragraph (in Chapter 13) to a phenomenon in 19th-century New Zealand history termed the Musket Wars, as an illustration of how powerful new technologies spread. The Musket Wars were a complicated, poorly understood series of tribal wars among New Zealand’s indigenous Maori people, between 1818 and the 1830s—wars by which European guns spread among tribes that had previo
usly fought one another with stone and wooden weapons. Two books published since then have increased our understanding of that chaotic period of New Zealand history, placed it in a broader historical context, and made its relevance to GGS even clearer.
In the early 1800s, European traders, missionaries, and whalers began to visit New Zealand, which had been occupied 600 years previously by Polynesian farmers and fishermen known as Maoris. The first European visitors were concentrated at New Zealand’s northern end. Those northern Maori tribes with the earliest access to Europeans thereby became the first tribes to acquire muskets, which gave them a big military advantage over all the other tribes lacking muskets. They used that advantage to settle scores with neighboring tribes that were their traditional enemies. But they also used muskets for a new type of warfare: long-distance raids against Maori tribes hundreds of miles away, carried out in order to outdo rivals in acquiring slaves and prestige.
At least as important as European muskets in making long-distance raids feasible were European-introduced potatoes (originating in South America), which yielded many more tons of food per acre or per farmer than did traditional Maori agriculture based on sweet potatoes. The main limitation that had previously prevented Maoris from undertaking long raids had been the twin problems of feeding warriors away from home for a long time, and feeding the at-home population of women and children dependent on the would-be warriors to stay home and grow sweet potatoes. Potatoes solved that bottleneck. Hence a less heroic term for the Musket Wars would be the Potato Wars.
Whatever they are called, the Musket/Potato Wars proved very destructive, killing about one-quarter of the original Maori population. The highest body counts arose when a tribe with lots of muskets and potatoes attacked a tribe with few or none. Of the tribes not among the first to acquire muskets and potatoes, some were virtually exterminated before they could acquire them, while others made determined efforts to acquire them and thereby restore the previous military equilibrium. One episode in these wars was the conquest and mass killing of Moriori tribes by Maori tribes, as described in Chapter 2.
The Musket/Potato Wars illustrate the main process running through the history of the last 10,000 years: human groups with guns, germs, and steel, or with earlier technological and military advantages, spreading at the expense of other groups, until either the latter groups became replaced or everyone came to share the new advantages. Recent history furnishes innumerable examples as Europeans expanded to other continents. In many places the non-European locals never got a chance to acquire guns and ended up losing their lives or their freedom. However, Japan did succeed in acquiring (actually, reacquiring) guns, preserved its independence, and within 50 years used its new guns to defeat a European power in the Russo-Japanese war of 1904–5. North American Plains Indians, South American Araucanian Indians, New Zealand’s Maoris, and Ethiopians acquired guns and used them to hold off European conquest for a long time, though they were ultimately defeated. Today, Third World countries are doing their best to catch up with the First World by acquiring the latter’s technological and agricultural advantages. Such spreads of technology and agriculture, arising ultimately from competition between human groups, must have happened at innumerable other times and places over the past 10,000 years.
In that sense, there was nothing unusual about New Zealand’s Musket/Potato Wars. While those wars were a purely local phenomenon confined to New Zealand, they are of worldwide interest because they furnish such a clear example, so narrowly confined in space and time, of so many other similar local phenomena. Within about two decades following their introduction to the northern end of New Zealand, muskets and potatoes had spread 900 miles to the southern end of New Zealand. In the past, agriculture, writing, and improved pre-gun weapons took much longer to spread much greater distances, but the underlying social processes of population replacement and competition were essentially the same. Now we are wondering whether nuclear weapons will proliferate around the world by the same often-violent process, from the eight countries that presently possess them.
A SECOND AREA of active discussion since 1997 falls under a heading that could be termed “Why Europe, not China?” Most of GGS concerned differences between continents: i.e., the question of why some Eurasians rather than Aboriginal Australians, sub-Saharan Africans, or Native Americans were the ones to expand over the world within the past millennium. However, I realized that many readers would also wonder “Why, among Eurasians, was it Europeans rather than Chinese or some other group that expanded?” I knew that my readers would not let me get away with concluding GGS without saying anything about this obvious question.
Hence I briefly considered it in the book’s epilogue. I suggested that the underlying reason behind Europe’s overtaking China was something deeper than the proximate factors suggested by most historians (e.g., China’s Confucianism vs. Europe’s Judeo-Christian tradition, the rise of western science, the rise of European mercantilism and capitalism, Britain’s deforestation coupled with its coal deposits, etc.). Behind these and other proximate factors, I saw an “Optimal Fragmentation Principle”: ultimate geographic factors that led to China becoming unified early and mostly remaining unified thereafter, while Europe remained constantly fragmented. Europe’s fragmentation did, and China’s unity didn’t, foster the advance of technology, science, and capitalism by fostering competition between states and providing innovators with alternative sources of support and havens from persecution.
Historians have subsequently pointed out to me that Europe’s fragmentation, China’s unity, and Europe’s and China’s relative strengths were all more complex than depicted in my account. The geographic boundaries of the political/social spheres that could usefully be grouped as “Europe” or “China” fluctuated over the centuries. China led Europe in technology at least until the 15th century and might do so again in the future, in which case the question “Why Europe, not China?” might only refer to an ephemeral phenomenon without deep explanation. Political fragmentation has more complex effects than only providing a constructive forum for competition: for instance, competition can be destructive as well as constructive (think of World Wars I and II). Fragmentation itself is a multifaceted rather than a monolithic concept: its effect on innovation depends on factors such as the freedom with which ideas and people can move across the boundaries between fragments, and whether the fragments are distinct or just clones of each other. Whether fragmentation is “optimal” may also vary with the measure of optimality used; a degree of political fragmentation that is optimal for technological innovation may not be optimal for economic productivity, political stability, or human happiness.
My sense is that a large majority of social scientists still favors proximate explanations for the different courses of European and Chinese history. For example, in a thoughtful recent essay Jack Goldstone stressed the importance of Europe’s (especially Britain’s) “engine science,” meaning the applications of science to the development of machines and engines. Goldstone wrote, “Two problems faced all pre-industrial economies in regard to energy: amount and concentration. The amount of mechanical energy available to any pre-industrial economy was limited to water flows, animals or people who could be fed, and wind that could be captured. In any geographically fixed area, this amount was strictly limited.…It is difficult to overstate the advantage given to the first economy or military/political power to devise a means to extract useful work from the energy in fossil fuels…. [It was] the application of steam power to spinning, to water and surface transport, to brick-making, grain-threshing, iron-making, shoveling, construction, and all sorts of manufacturing processes that transformed Britain’s economy…. It thus may be that, far from a necessary development of European civilization, the rich development of engine science was the chance outcome of specific, even if highly contingent, circumstances that happened to arise in 17th- and 18th-century Britain.” If this reasoning is correct, then a search for deep geographic or ecological explanat
ions will not be profitable.
The opposite minority view, similar to my view expressed in the epilogue of GGS, has been argued in detail by Graeme Lang: “Differences between Europe and China in ecology and geography helped to explain the very different fates of science in the two regions. First, [rainfall] agriculture in Europe provided no role for the state, which remained far from local communities most of the time, and when the agricultural revolution in Europe produced a growing agricultural surplus, this allowed the growth of relatively autonomous towns along with urban institutions such as universities prior to the rise of the centralized states in the late Middle Ages. [Irrigation and water-control] agriculture in China, by contrast, favored the early development of intrusive and coercive states in the major river valleys, while towns and their institutions never achieved the degree of local autonomy found in Europe. Second, the geography of China, unlike that of Europe, did not favor the prolonged survival of independent states. Instead, China’s geography facilitated eventual conquest and unification over a vast area, followed by long periods of relative stability under imperial rule. The resulting state system suppressed most of the conditions required for the emergence of modern science…. The explanation outlined above is certainly oversimplified. However, one of the advantages of this kind of account is that it escapes the circularity which often creeps into explanations which do not go deeper than social or cultural differences between Europe and China. Such explanations can always be challenged with a further question: why were Europe and China different with regard to those social or cultural factors? Explanations rooted ultimately in geography and ecology, however, have reached bedrock.”
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