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GUNS, GERMS AND STEEL, CH.10

GUNS, GERMS AND STEEL, CH.10 - CHAPTER 10 SPACIOUS SKIES...

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Unformatted text preview: CHAPTER 10 SPACIOUS SKIES AND TILTED AXES O N THE MAP OF THE WORLD ON PAGE 177 (EicunE 10.1}. compare the shapes and orientations of the continents. You’ll ht- 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 w1dest, 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 truci 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 111 the orien- tation of the continents’ axes have on human history? This chapter will be about what 1 see as their enormous, sometimes tragic, consequences. Axis orientations affected the rate of spread of crops and l1vestock, 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. F001) PRODUCTION’S SPREAD proves as crucial to understanding geographlc dlfferences 1n 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 SPACIOUS SKIES AND TiLTED AXES ' I 7 7 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 other 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, 1n 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 Southeast 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 producrion existed nearby. The most conspicuous such examples are the failure of both farming and herding to reach Native I 7 8 - GUNS, GERMS. AND STEEL American California from the US. Southwest or to reach Australia fro New Guinea and Indonesia, and the failure of farming to spread from South Africa’s Natal Province to South Africa’s Cape. Even amon all those areas where food production did spread in the prehistoric erag th rates and dates of spread varied considerably. At the one extreme w l ' '3 rapid spread along east—West axes: from Southwest Asia both we: its Europe and Egypt and east to the Indus Valley (at an average rate of about 0.7 nules 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 5 Southwest; at less than 0.3 miles per year, for corn and beans from Mexii A northward to become productive in the eastern United States around A :0 900; and at 0.2 miles per year, for the llama from Peru north to Ecuado ' These differences could be even greater if corn was not domesticated iii lviexrco as late as 3500 3.0., as I assumed conservatively for these calcula— Epgfidand as some archaeologists now assume, but if it was instead domes- many stpfirjéjlerably earlier, as most archaeologists used to assume (and There were also great differences in the completeness with which suite of crops and livestock spread, again implying stronger or weaker bartie S to their spreading. For instance, while most of Southwest Asia’s found” crops and livestock did spread west to Europe and east to the Indus V ll er neither of the Andes’ domestic mammals (the llama] alpaca and the 3' 6y, pig) ever reached Mesoamerica in pre-Columbian times. That ”refill: failure cries out for explanation. After all, Mesoamerica did develop dense farmmg populations and_complex societies, so there can be no doubt that Andean domestic animals (if they had been available) would have bee valuable for food, transport, and wool. Except for dogs Mesoameric n utterly without indigenous mammals to fill those needs.,Some South :1: as ican crops nevertheless did succeed in reaching Mesoamerica such as maet: me, sweet potatoes, and peanuts. What selective barrier ldt those Cr through but screened out llamas and guinea pigs? Ops A subtler expression of this geographically varying ease of spread is the phenomenon termed preemptive domestication. Most of the wild lan speCies from which our crops were derived vary genetically from at: I area, because alternative mutations had become established amon atho wrld. ancestral p0pulations of different areas. Similarly the chag a required to transform wild plants into crops can in principle be brunt: SPACIOUS SKIES AND TILTED AXES " I 7 9 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 ether varieties of the same crop inherited the mutation of another area. On this basis, botanists conclude that lima beans (Pbaseolus Iunatus), common beans (Pbaseolus vulgaris), 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 Southwesr Asia, but frequent multiple domestications in the Americas, might thus provide r 3 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 thereland vice versa). Chili peppers, squashes, amaranths, and chenopods are other crops of which different but related species were domesricated 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 tedornestications of the same species or domesrications 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 producrion 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 :2 i i s .5 SPACIOUS SKIES AND TILTED axes - 1 8 1 farther and farther removed from the Fertile Crescent, to the west an: east. On this page I have redrawn the striking map (Etgure 10.2) assekrpbtlle by the geneticist Daniel Zohary and botanist Maria Hopf, m whic :1. ey illustrate how the wave had reached Greece and Cyprus and the In tan subcontinent by 6500 ac, Egypt soon after 6000 B.C., central Europe by 5400 B.C., southern Spain by 5200 B.C., 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. ln‘addition, the Fertile Crescent package penetrated Africa 00“?- ward to Ethiopia at some still-uncertaindate. However, Ethiopia a so developed many indigenous crops, and we do not yet know whethelr‘it was these crops or the arriving Fertile Crescent crops that launched Et topian food production. The spread of Fertile Crescent crops across western Eurasia ' ' " - _ braces, u belore 7000 BC Figure 10.2. The symbols Show early radiocarbOri-dated sites wherec ‘ remains of Fertile Crescent crops have been found. [3 = the Fertile ‘ rles- cent itself (sites before 7000 B.C.). Note that dates become progress;ve y later as one gets farther from the Fertile Crescent. This map is baseWonld Map 20 of Zobary and Hopf’s Domestication of Plants in the Old or but substitutes calibrated radiocarbon dates for their uncalibrated dates. 1 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 1n 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 wesr 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 iri 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 insrance, 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 TlLTED AXES I 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 satiuum, the one that became domesticated to yield our garden peas, and Pisum fulvum, which was never domesti- cated. Yet wild peas of Pisum fuluum 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 Penile 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 are 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 an5wer depends partly on that east—west axis of Eurasia with which i opened this chapter. Localities disrributed 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, Portugal, northern Iran, and 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 type r 8 4 - GUNS, oEitMs. AND STEEL 'known as tropical rain forest is confined to within about 10 degrees lati- tude of the equator, while Mediterranean scrub habitats (such as Califor— nia’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—{he 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 kick 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 ai the equator. Animals too are adapted to latitude-related featu...
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