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diamond sec 2 - m DIMc/xb CHAPTER 10 SPACIOUS SKIES AND...

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Unformatted text preview: m DIMc/xb CHAPTER 10 SPACIOUS SKIES AND TILTED AXES N THE MAP or THE WORLD 0N PAGE 177 (FIGURE 10.1), compare the shapes and orientations of the continents. You’ll be struck by an obvious difference. The Americas span a much greater dis- tance north-south (9,000 miles) than east-west: only 3,000 miles at the widest, narrowing to a mere 40 miles at the Isthmus of Panama. That is, the major axis of the Americas is north—south. The same is also true, though to a less extreme degree, for Africa. In contrast, the major axis of Eurasia is east-west. What effect, if any, did those differences in the orien- tation of the continents‘ axes have on human history? This chapter will be about what I see as their enormous, sometimes tragic, consequences. Axis orientations affected the rate of spread of crops and livestock, and possibly also of writing, wheels, and other inventions. That basic feature of geography thereby contributed heavily to the very different experiences of Native Americans, Africans, and Eurasians in the last 500 years. Fooo PRODUCTION’S SPREAD proves as crucial to understanding geographic differences in the rise of guns, germs, and steel as did its ori- gins, which we considered in the preceding chapters. That's because, as we 176 Figure 10.1. Major axes of the continents. saw in Chapter 5, there were no more than nine areas of the globe, perhaps as few as five, where food production arose independently. Yet, already in prehistoric times, food production became established in many orher regions besides those few areas of origins. All those other areas became food producing as a result of the spread of crops, livestock, and knowledge of how to grow them and, in some cases, as a result of migrations of farm- ers and herders themselves. The main such spreads of food production were from Southwest Asia to Europe, Egypt and North Africa, Ethiopia, Central Asia, and the Indus Valley; from the Sahel and West Africa to East and South Africa; from China to tropical Scutheast Asia, the Philippines, Indonesia, Korea, and Japan; and from Mesoamerica to North America. Moreover, food produc- tion even in its areas of origin became enriched by the addition of crops, livestock, and techniques from other areas of origin. Just as some regions proved much more suitable than others for the origins of food production, the ease of its spread also varied greatly around the world. Some areas that are ecologically very suitable for food production never acquired it in prehistoric times at all, even though areas of prehistoric food production existed nearby. The most conspicuous such examples are the failure of both farming and herding to reach Native ,Avr. American California from the U.S. Southwest or to reach Australia from New Guinea and Indonesia, and the failure of farming to spread from South Africa’s Natal Province to South Africa’s Cape. Even among all those areas where food production did spread in the prehistoric era, the rates and dates of spread varied considerably. At the one extreme was its rapid spread along east—west axes: from Southwest Asia both west to Europe and Egypt and east to the Indus Valley (at an average rate of about 0.7 miles per year); and from the Philippines east to Polynesia (at 3.2 miles per year). At the opposite extreme was its slow spread along north—south axes: at less than 0.5 miles per year, from Mexico northward to the U.S. Southwest; at less than 0.3 miles per year, for corn and beans from Mexico northward to become productive in the eastern United States around A.D. 900; and at 0.2 miles per year, for the llama from Peru north to Ecuador. These differences could be even greater if corn was not domesticated in Mexico as late as 3500 B.C., as I assumed conservatively for these calcula- tions, and as some archaeologists now assume, but if it was instead domes- ticated considerably earlier, as most archaeologists used to assume (and many still do). There were also great differences in the completeness with which suites of crops and livestock spread, again implying stronger or weaker barriers to their spreading. For instance, while most of Southwest Asia’s founder crops and livestock did spread west to Europe and east to the Indus Valley, neither of the Andes’ domestic mammals (the llama / alpaca and the guinea pig) ever reached Mesoamerica in pre-Columbian times. That astonishing failure cries out for explanation. After all, Mesoamerica did develop dense farming populations and complex societies, so there can be no doubt that Andean domestic animals (if they had been available) would have been valuable for food, transport, and wool. Except for dogs, Mesoamerica was utterly without indigenous mammals to fill those needs. Some South Amer- ican crops nevertheless did succeed in reaching Mesoamerica, such as man- ioc, sweet potatoes, and peanuts. What selective barrier let those crops through but screened out llamas and guinea pigs? A subtler expression of this geographically varying ease of spread is the phenomenon termed preemptive domeStication. Most of the wild plant species from which our crops were derived vary genetically from area to area, because alternative mutations had become established among the wild ancestral populations of different areas. Similarly, the changes required to transform wild plants into crops can in principle be brought about by alternative new mutations or alternative courses of selection to yield equivalent results. In this light, one can examine a crop widespread in prehistoric times and ask whether all of its varieties show the same wild mutation or same transforming mutation. The purpose of this examina- tion is to try to figure out whether the crop was developed in just one area or else independently in several areas. If one carries out such a genetic analysis for major ancient New World crops, many of them prove to include two or more of those alternative wild variants, or two or more of those alternative transforming mutations. This suggests that the crop was domesticated independently in at least two different areas, and that some varieties of the crop inherited the particular mutation of one area while other varieties of the same crop inherited the mutation of another area. On this basis, botanists conclude that lima beans (Pbaseolus hmatus), common beans (Pbaseolus uulgaris), and chili peppers of the Capsicum annuum / chinense group were all domesticated on at least two separate occasions, once in Mesoamerica and once in South America; and that the squash Cucurbita pepo and the seed plant goosefoot were also domesticated independently at least twice, once in Mesoamerica and once in the eastern United States. In contrast, most ancient Southwest Asian crops exhibit just one of the alternative wild variants or alternative transforming mutations, suggesting that all modern varieties of that partic- ular crop stem from only a single domestication. What does it imply if the same crop has been repeatedly and indepen- dently domesticated in several different parts of its wild range, and not juSt once and in a single area? We have already seen that plant domestica~ tion involves the modification of wild plants so that they become more useful to humans by virtue of larger seeds, a less bitter taste, or other qualities. Hence if a productive crop is already available, incipient farmers will surely proceed to grow it rather than start all over again by gathering its not yet so useful wild relative and redomesticating it. Evidence for just a single domestication thus suggests that, once a wild plant had been domesticated, the crop spread quickly to other areas throughout the wild plant’s range, preempting the need for other independent domestications of the same plant. However, when we find evidence that the same wild ancestor was domesticated independently in different areas, we infer that the crop spread too slowly to preempt its domestication elsewhere. The evidence for predominantly single domestications in Southwest Asia, but frequent multiple domestications in the Americas, might thus provide I 8 O ' GUNS, GERMS, AND STEEL more subtle evidence that crops spread more easily out of Southwest Asia than in the Americas. Rapid spread of a crop may preempt domestication not only of the same wild ancestral species somewhere else but also of related wild species. If you’re already growing good peas, it’s of course pointless to start from scratch to domesticate the same wild ancestral pea again, but it’s also pointless to domesticate closely related wild pea species that for farmers are virtually equivalent to the already domesticated pea species. All of Southwest Asia’s founder crops preempted domestication of any of their close relatives throughout the whole expanse of western Eurasia. In con- trast, the New World presents many cases of equivalent and closely re- lated, but nevertheless distinct, species having been domesticated in Meso- america and South America. For instance, 95 percent of the cotton grown in the world today belongs to the cotton species Gossypium hirsutum, which was domesticated in prehistoric times in Mesoamerica. However, prehistoric South American farmers instead grew the related cotton Gos- sypium barbadense. Evidently, Mesoamerican cotton had such difficulty reaching South America that it failed in the prehistoric era to preempt the domestication of a different cotton species there (and vice versa). Chili peppers, squashes, amaranths, and chenopods are other crops of which different but related species were domesticated in Mesoamerica and South America, since no species was able to spread fast enough to preempt the others. We thus have many different phenomena converging on the same con- clusion: that food production spread more readily out of Southwest Asia than in the Americas, and possibly also than in sub-Saharan Africa. Those phenomena include food production’s complete failure to reach some eco- logically suitable areas; the differences in its rate and selectivity of spread; and the differences in whether the earliest domesticated crops preempted redomestications of the same species or domestications of close relatives. What was it about the Americas and Africa that made the spread of food production more difficult there than in Eurasia? To ANSWER THIS question, let’s begin by examining the rapid spread of food production out of Southwest Asia (the Fertile Crescent). Soon after food production arose there, somewhat before 8000 B.C., a centrifugal wave of it appeared in other parts of western Eurasia and North Africa SPACIOUS SKIES AND TILTED AXES ' I 8 I farther and farther removed from the Fertile Crescent, to the west and east. On this page I have redrawn the striking map (Figure 10.2) assembled by the geneticist Daniel Zohary and botanist Maria Hopf, in which they illustrate how the wave had reached Greece and Cyprus and the Indian subcontinent by 6500 B.C., Egypt soon after 6000 a.c., central Europe by 5400 no, southern Spain by 5200 13.0., and Britain around 3500 B.C. In each of those areas, food production was initiated by some of the same suite of domestic plants and animals that launched it in the Fertile Cres- cent. In addition, the Fertile Crescent package penetrated Africa south- ward to Ethiopia at some still-uncertain date. However, Ethiopia also developed many indigenous crops, and we do not yet know whether it was these crops or the arriving Fertile Crescent crops that launched Ethiopian food production. a before 7000 so I 7000~6000 so 0 6000-5000 no A 5000-3800 ac A 3800-250030 Figure 10.2. The symbols show early radiocarbon-dated sites where remains of Fertile Crescent crops hat/germ found. Cl = the Fertile Cres- cent itself {sites before 7000 ac). Note that dates become progressively later as one gets farther from the Fertile Crescent. This map is based on Map 20 of Zohary and Hop/’5 Domestication of Plants in~the Old World but substitutes calibrated radiocarbon dates for their uncalibrated dates. r 8 2 - GUNS. GERMS, AND STEEL Of course, not all pieces of the package spread to all those outlying areas: for example, Egypt was too warm for einkorn wheat to become established. In some outlying areas, elements of the package arrived at different times: for instance, sheep preceded cereals in southwestern Europe. Some outlying areas went on to domesticate a few local crops of their own, such as poppies in western Europe and watermelons possibly in Egypt. But most food production in outlying areas depended initially on Fertile Crescent domesticates. Their spread was soon followed by that of other innovations originating in or near the Fertile Crescent, including the wheel, writing, metalworking techniques, milking, fruit trees, and beer and wine production. Why did the same plant package launch food production throughout western Eurasia? Was it because the same set of plants occurred in the wild in many areas, were found useful there just as in the Fertile Crescent, and were independently domesticated? No, that’s not the reason. First, many of the Fertile Crescent’s founder crops don’t even occur in the wild outside Southwest Asia. For instance, none of the eight main founder crops except barley grows wild in Egypt. Egypt’s Nile Valley provides an environment similar to the Fertile Crescent’s Tigris and Euphrates Valleys. Hence the package that worked well in the latter valleys also worked well enough in the Nile Valley to trigger the spectacular rise of indigenous Egyptian civilization. But the foods to fuel that spectacular rise were originally absent in Egypt. The sphinx and pyramids were built by people fed on crops originally native to the Fertile Crescent, not to Egypt. Second, even for those crops whose wild ancestor does occur outside of Southwest Asia, we can be confident that the crops of Europe and India were mostly obtained from Southwest Asia and were not local domesti- cates. For example, wild flax occurs west to Britain and Algeria and east to the Caspian Sea, while wild barley occurs east even to Tibet. However, for most of the Fertile Crescent’s founding crops, all cultivated varieties in the world today share only one arrangement of chromosomes out of the multiple arrangements found in the wild ancestor; or else they share only a single mutation (out of many possible mutations) by which the cultivated varieties differ from the wild ancestor in characteristics desirable to humans. For instance, all cultivated peas share the same recessive gene that prevents ripe pods of cultivated peas from spontaneously popping open and spilling their peas, as wild pea pods do. Evidently, most of the Fertile Crescent’s founder crops were never SPACIOUS SKIES AND TILTED AXES ' I 8 3 domesticated again elsewhere after their initial domestication in the Fertile Crescent. Had they been repeatedly domesticated independently, they would exhibit legacies of those multiple origins in the form of varied chro- mosomal arrangements or varied mutations. Hence these are typical exam- ples of the phenomenon of preemptive domestication that we discussed above. The quick spread of the Fertile Crescent package preempted any possible other attempts, within the Fertile Crescent or elsewhere, to domesticate the same wild ancestors. Once the crop had become available, there was no further need to gather it from the wild and thereby set it on the path to domestication again. The ancestors of most of the founder crops have wild relatives, in the Fertile Crescent and elsewhere, that would also have been suitable for domestication. For example, peas belong to the genus Pisum, which con- sists of two wild species: Pisum sativum, the one that became domesticated to yield our garden peas, and Pisum fuluum, which was never domesti- cated. Yet wild peas of Pisum full/um taste good, either fresh or dried, and are common in the wild. Similarly, wheats, barley, lentil, chickpea, beans, and flax all have numerous wild relatives besides the ones that became domesticated. Some of those related beans and barleys were indeed domes- ticated independently in the Americas or China, far from the early site of domestication in the Fertile Crescent. But in western Eurasia only one of several potentially useful wild species was domesticated—probably because that one spread so quickly that people soon stopped gathering the other wild relatives and ate only the crop. Again as we discussed above, the crop’s rapid spread preempted any possible further attempts to domes— ticate its relatives, as well as to redomesticate its ancestor. WHY WAS THE spread of crops from the Fertile Crescent so rapid? The answer depends partly on that east—west axis of Eurasia with which I opened this chapter. Localities distributed east and west of each other at the same latitude share exactly the same day length and its seasonal varia- tions. To a lesser degree, they also tend to share similar diseases, regimes of temperature and rainfall, and habitats or biomes (types of vegetation). For example, southern Italy, northern Wand Japan, all located at about the same latitude but lying successively 4,000 miles east or west of each other, are more similar to each other in climate than each is to a location lying even a mere 1,000 miles due south. On all the continents the habitat l l l I 8 4 - GUNS. GERMS, AND STEEL type known as tropical rain forest is confined to within about 10 degrees latitude of the equator, while Mediterranean scrub habitats (such as Cali- fornia’s Chaparral and Europe’s maquis) lie between about 30 and 40 degrees of latitude. But the germination, growth, and disease resistance of plants are adapted to precisely those features of climate. Seasonal changes of day length, temperature, and rainfall constitute signals that stimulate seeds to germinate, seedlings to grow, and mature plants to develop flowers, seeds, and fruit. Each plant population becomes genetically programmed, through natural selection, to respond appropriately to signals of the sea- sonal regime under which it has evolved. Those regimes vary greatly with latitude. For example, day length is constant throughout the year at the equator, but at temperate latitudes it increases as the months advance from the winter solstice to the summer solstice, and it then declines again through the next half of the year. The growing season—that is, the months with temperatures and day lengths suitable for plant growth—is shortest at high latitudes and longest toward the equator. Plants are also adapted to the diseases prevalent at their latitude. Woe betide the plant whose genetic program is mismatched to the lati- tude of the field in which it is planted! Imagine a Canadian farmer foolish enOugh to plant a race of corn adapted to growing farther south, in Mex- ico. The unfortunate corn plant, following its Mexico-adapted genetic pro- gram, would prepare to thrust up its shoots in March, only to find itself still buried under 10 feet of snow. Should the plant become genetically reprogrammed so as to germinate at a time more appropriate to Canada—— say, late june—the plant would still be in trouble for other reasons. Its genes would be telling it to grow at a leisurely rate, sufficient only to bring it to maturity in five months. That’s a perfectly safe strategy in Mexico's mild climate, but in Canada a disastrous one that would guarantee the plant’s being killed by autumn frosts before it had produced any mature corn cobs. The plant would also lack genes for resistance to diseases of northern climates, while uselessly carrying genes for resistance to diseases of southern climates. All those features make low-latitude plants poorly adapted to high-latitude conditions, and vice versa. As a consequence, most Fertile Crescent crops grow well in France and Japan but poorly at the equator. Animals too are adapted to latitude-related features of climate. In that respect we are typical animals, as we know by introspection. Some of us v i l SPACIOUS SKIES AND TILTED AXES ' I 8 5 can’t stand cold northern winters with their short days and characteristic germs, while others of us can’t stand hot tropical climates with their own characteristic diseases. In recent centuries overseas colonists from cool northern Europe have preferred to emigrate to the similarly cool climates of North America, Australia, and South Africa, and to settle in the cool highlands within equatorial Kenya and New Guinea. Northern Europeans who were sent out to hot tropical lowland areas used to die in droves of diseases such as malaria, to which tropical peoples had evolved some genetic resistance. That’s part of the reason why Fertile Crescent domesticates spread west and east so rapidly: they were already well adapted to the climates of the regions to which they were spreading. For instance, once farming crossed from the plains of Hungary into central Europe around 5400 B.C., it spread so quickly that the sites of the first farmers in the vast area from Poland west to Holland (marked by their characteristic pottery with linear decorations) were nearly contemporaneous. By the time of Christ, cereals of Fertile Crescent origin were growing over the 10,000—mile expanse from ,the Atlantic coast of Ireland to the Pacific coast of Japan. That west-east S expanse of Eurasia is the largest land distance on Earth. Thus, Eurasia’s west—east axis allowed Fertile Crescent crops quickly to launch agriculture over the band of temperate latitudes from Ireland to the Indus Valley, and to enrich the agriculture that arose independently in east- ern Asia. Conversely, Eurasian crops that were first domesticated far from the Fertile Crescent but at the same latitudes were able to diffuse back to the Fertile Crescent. Today, when seeds are transported over the whole globe by ship and plane, we take it for granted that our meals are a geo- graphic mishmash. A typical American fast-food restaurant meal would include chicken (first domesticated in China) and potatoes (from the Andes) or corn (from Mexico), seasoned with black pepper (from India) and washed down with a cup of coffee (of Ethiopian origin). Already, though, by 2,000 years ago, Romans were also nourishing themselves with their own hodgepodge of foods that mostly originated elsewhere. Of Roman crops, only oats and poppies were native to Italy. Roman staples were the Fertile Crescent founder~package, supplemented by quince (origi- nating in the Caucasus); millet and cumin (domesticated in Central Asia); cucumber, sesame, and citrus fruit (from India); and chicken, rice, apri- cots, peaches, and foxtail millet (originally from China). Even though Rome’s apples were at least native to western Eurasia, they were grown I 8 6 - GUNS, GERMS, AND STEEL by means of grafting techniques that had developed in China and spread westward from there. While Eurasia provides the world’s widest band of land at the same latitude, and hence the most dramatic example of rapid spread of domesti- cates, there are other examples as well. Rivaling in speed the spread of the Fertile Crescent package was the eastward spread of a subtropical package that was initially assembled in South China and that received additions on reaching tropical Southeast Asia, the Philippines, Indonesia, and New Guinea. Within 1,600 years that resulting package of crops (including bananas, taro, and yarns) and domestic animals (chickens, pigs, and dogs) had spread more than 5,000 miles eastward into the tropical Pacific to reach the islands of Polynesia. A further likely example is the east-west spread of crops within Africa’s wide Sahel zone, but paleobotanists have yet to work out the details. CONTRAST THE EASE of east—west diffusion in Eurasia with the diffi- culties of diffusion along Africa’s north—south axis. Most of the Fertile Crescent founder crops reached Egypt very quickly and then spread as far “ south as the cool highlands of Ethiopia, beyond which they didn’t spread. South Africa’s Mediterranean climate would have been ideal for them, but the 2,000 miles of tropical conditions between Ethiopia and South Africa posed an insuperable barrier. Instead, African agriculture south of the Sahara was launched by the domestication of wild plants (such as sorghum and African yarns) indigenous to the Sahel zone and to tropical West Africa, and adapted to the warm temperatures, summer rains, and rela- tively constant day lengths of those low latitudes. Similarly, the spread southward of Fertile Crescent domestic animals through Africa was stopped or slowed by climate and disease, especially by trypanosome diseases carried by tsetse flies. The horse never became established farther south than West Africa’s kingdoms north of the equa- tor. The advance of cattle, sheep, and goats halted for 2,000 years at the northern edge of the Serengeti Plains, while new types of human econo- mics and livestock breeds were being developed. Not until the period A.D. 1-200, some 8,000 years after livestock were domesticated in the Fertile Crescent, did cattle, sheep, and goats finally reach South Africa. Tropical African crops had their own difficulties spreading south in Africa, arriving in South Africa with black African farmers (the Bantu) just after those ‘_ ,.__ "Aflvav.___ l | l 1 SPACIOUS SKIES AND TILTED AXES ' l 8 7 Fertile Crescent livestock did. However, those tropical African crops could never be transmitted across South Africa’s Fish River, beyond which they were stopped by Mediterranean conditions to which they were not adapted. The result was the all-too-familiar course of the last two millennia of South African history. Some of South Africa’s indigenous Khoisan peoples (otherwise known as Hottentots and Bushmen) acquired livestock but remained without agriculture. They became outnumbered and were replaced northeast of the Fish River by black African farmers, whose southward spread halted at that river. Only when European settlers arrived by sea in 1652, bringing with them their Fertile Crescent crop package, could agriculture thrive in South Africa’s Mediterranean zone. The collisions of all those peoples produced the tragedies of modern South Africa: the quick decimation of the Khoisan by European germs and guns; a century of wars between Europeans and blacks; another century of racial oppression; and now, efforts by Europeans and blacks to seek a new mode of coexistence in the former Khoisan lands. Commas-r ALSO THE ease of diffusion in Eurasia with its difficulties along the Americas’ north—south axis. The distance between Mesoamerica and South America—say, between Mexico’s highlands and Ecuador’s—is only 1,200 miles, approximately the same as the distance in Eurasia sepa- rating the Balkans from Mesopotamia. The Balkans provided ideal grow- ing conditions for most Mesopotamian crops and livestock, and received those domesticates as a package within 2,000 years of its assembly in the Fertile Crescent. That rapid spread preempted opportunities for domesti- cating those and related species in the Balkans. Highland Mexico and the Andes would similarly have been suitable for many of each other’s crops and domestic animals. A few crops, notably Mexican corn, did indeed spread to the other region in the pre-Columbian era. But other crops and domestic animals failed to spread between Meso- america and South America. The cool highlands of Mexico would have provided ideal conditions for raising llamas, guinea pigs, and potatoes, all domesticated in the cool highlands of the South American Andes. Yet the northward spread of those Alidegn specialties was stopped completely by the hot intervening lowlands of Central America. Five thousand years after llamas had been domesticated in the Andes, the Olmecs, Maya, Aztecs, r 8 8 - GUNS. GERMS, AND STEEL and all other native societies of Mexico remained without pack animals and without any edible domestic mammals except for dogs. Conversely, domestic turkeys of Mexico and domestic sunflowers of the eastern United States might have thrived in the Andes, but their southward spread was stopped by the intervening tropical climates. The mere 700 miles of north-south distance prevented Mexican corn, squash, and beans from reaching the US. Southwest for several thousand years after their domestication in Mexico, and Mexican chili peppers and chenopods never did reach it in prehistoric times. For thousands of years after corn was domesticated in Mexico, it failed to spread northward into eastern North America, because of the cooler climates and shorter growing season pre' vailing there. At some time between A.D. 1 and A.D. 200, com finally appeared in the eastern United States but only as a very minor crop. Not until around AD. 900, after hardy varieties of corn adapted to northern climates had been developed, could corn-based agriculture contribute to the flowering of the most complex Native American society of North America, the Mississippian culture—a brief flowering ended by European- introduced germs arriving with and after Columbus. Recall that most Fertile Crescent crops prove, upon genetic study, to derive from only a single domestication process, whose resulting crop spread so quickly that it preempted any other incipient domestications of the same or related species. In contrast, many apparently widespread Native American crops prove to consist of related species or even of geneti- cally distinct varieties of the same species, independently domesticated in Mesoamerica, South America, and the eastern United States. Closely related species replace each other geographically among the amaranths, beans, chenopods, chili peppers, cottons, squashes, and tobaccos. Differ- ent varieties of the same species replace each other among the kidney beans, lima beans, the chili pepper Capsicum annuum/ chinense, and the squash Cucurbita pepo. Those legacies of multiple independent domestica- tions may provide further testimony to the slow diffusion of crops along the Americas’ north—south axis. I Africa and the Americas are thus the two largest landmasses with a predominantly north-south axis and resulting slow diffusion. In certain . other parts of the world, slow north—south diffusion was important on a 1 smaller scale. These other examples include the snail’s pace of crop exchange between Pakistan’s Indus Valley and South India, the slow spread of South Chinese food production into Peninsular Malaysia, and ...,_- ~.4 ____..____.‘__,_ .. “%WV.VWV.I -v..... SPACIOUS SKIES AND TILTED AXES ' I 8 9 the failure of tropical Indonesian and New Guinean food production to arrive in prehistoric times in the modern farmlands of southwestern and southeastern Australia, respectively. Those two corners of Australia are now the continent’s breadbaskets, but they lie more than 2,000 miles south of the equator. Farming there had to await the arrival from faraway Europe, on European ships, of crops adapted to Europe’s cool climate and short growing season. I HAVE BEEN dwelling on latitude, readily assessed by a glance at a map, because it is a major determinant of climate, growing conditions, and ease of spread of food production. However, latitude is of course not the only such determinant, and it is not always true that adjacent places at the same latitude have the same climate (though they do necessarily have the same day length). Topographic and ecological barriers, much more pronounced on some continents than on others, were locally important obstacles to diffusion. For instance, crop diffusion between the US. Southeast and Southwest was very slow and selective although these two regions are at the same latitude. That’s because much of the intervening area of Texas and the southern Great Plains was dry and unsuitable for agriculture. A corres- ponding example within Eurasia involved the eastern limit of Fertile Cres- cent crops, which spread rapidly westward to the Atlantic Ocean and eastward to the Indus Valley without encountering a major barrier. How- ever, farther eastward in India the shift from predominantly winter rainfall to predominantly summer rainfall contributed to a much more delayed extension of agriculture, involving different crops and farming techniques, into the Ganges plain of northeastern India. Still farther east, temperate areas of China were isolated from western Eurasian areas with similar climates by the combination of the Central Asian desert, Tibetan plateau, and Himalayas. The initial development of food production in China was therefore independent of that at the same latitude in the Fertile Crescent, and gave rise to entirely different crops. However, even those barriers between China and western Eurasia were at least partly overcome during the second millennium B.C., when West Asian wheat, barley, and horses reached China. By the same token, the petgncy of a 2,000-mile north-south shift as a barrier also varies with local conditions. Fertile Crescent food production I. 90 ' CUNS.GERMS.AND5TE1EL spread southward over that distance to Ethiopia, and Bantu food produc— tion spread quickly from Africa’s Great Lakes region south to Natal, because in both cases the intervening areas had similar rainfall regimes and were suitable for agriculture. In contrast, crop diffusion from Indone- sia south to southwestern Australia was completely impossible, and diffu- sion over the much shorter distance from Mexico to the U.S. Southwest and Southeast was slow, because the intervening areas were deserts hostile to agriculture. The lack of a high-elevation plateau in Mesoamerica south of Guatemala, and Mesoamerica’s extreme narrowness south of Mexico and especially in Panama, were at least as important as the latitudinal gradient in throttling crop and livestock exchanges between the highlands of Mexico and the Andes. Continental differences in axis orientation affected the diffusiori not only of food production but also of other technologies and inventions. For example, around 3,000 B.C. the invention of the wheel in or near South- west Asia spread rapidly west and east across much of Eurasia within a few centuries, whereas the wheels invented independently in prehistoric Mexico never spread south to the Andes. Similarly, the principle of alpha— betic writing, developed in the western part of the Fertile Crescent by 1500 B.C.._ spread west to Carthage and east to the indian subcontinent within about a thousand years, but the Mesoamerican writing systems that flour— ished in prehistoric times for at least 2,000 years never reached the Andes. Naturally, wheels and writing aren’t directly linked to latitude and day length in the way crops are. Instead, the links are indirect, especially via food production systems and their consequences. The earliest wheels were parts of oat-drawn carts used to transport agricultural produce. Early writ— ing was restricted to elites supported by food—producing peasants, and it served purposes of economically and socially complex food-producing societies (such as royal propaganda, goods inventories, and bureaucratic record keeping}. In general, societies that engaged in intense exchanges of crops, livestock, and technologies related to food production were more liker to become involved in other exchanges as well. America’s patriotic song “America the Beautiful” invokes our spacious skies, our amber waves of grain, from sea to shining sea. Actually, that song reverses ge0graphic realities. As in Africa, in the Americas the spread of native crops and domestic animals was slowed by constricted skies and environmental barriers. No waves of native grain ever stretched from the Atlantic to the Pacific coast of North America, from Canada to Patagonia, SPACIOUS SKIES AND TILTEDAXES ‘ .19 J. or from Egypt to South Africa, while amber waves of wheat and barley came to stretch from the Atlantic to the Pacific across the spacious skies of Eurasia. That faster spread of Eurasian agriculture, compared with that of Native American and sub-Saharan African agriculture, played a role (as the next part of this book will show} in the more rapid diffusion of Eur» asian writing, metallurgy, technology, and empires. To bring up all those differences isn’t to claim that widely distributed 1 crops are admirable, or that they testify to the superior ingenuity of early A Eurasian farmers. They reflect, instead, the orientation of Eurasia’s axis ; compared with that of the Americas or Africa. Around those axes turned l the fortunes of history. ...
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diamond sec 2 - m DIMc/xb CHAPTER 10 SPACIOUS SKIES AND...

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