Chapter 11 Chapter 10: The Wide Sky and Skewed Axis

Compare the shapes and axes of the continents on the world map (Figure 10.1) on the next page.You'll be impressed by a stark difference.The north-south distance of the Americas (9,000 miles) is much greater than the east-west distance: the widest point from east to west is only 3,000 miles, and the narrowest point is only 40 miles on the axis of Panama.That is, the main axis of the Americas runs north-south.The same is true in Africa, though to a lesser extent.In contrast, the main axis of Eurasia runs east-west.So, what impact did these differences in the orientation of continental axes have on human history?

This chapter discusses what I consider to be the dramatic and sometimes tragic consequences of differences in the orientation of the axes.The direction of the axis affected the speed at which crops and livestock spread, and possibly writing, the wheel, and other inventions.This basic geographic feature has contributed enormously to shaping the very different experiences of Indians, Africans, and Eurasians over the past 500 years. The spread of food production proved as crucial to understanding the geographic differences in the emergence of guns, germs, and steel as the origins of food production.The question of the origins of food production has been examined in previous chapters.As we saw in Chapter 5, this is because there are as many as nine regions of the planet that independently produce food and as few as five.However, in prehistoric times, in addition to these few birthplaces of food production, food production has also occurred in many other areas.Food production arose in all these other areas as a result of the spread of crops, livestock, and the knowledge of how to grow them and raise them, and in some cases, as a result of the migration of farmers and herders themselves.

The main routes for this spread 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 Central America to North America.Moreover, food production was enriched even in its origins by additional crops, livestock, and technologies from other origins. Just as certain regions proved more amenable to the emergence of food production than others, the ease with which food production spread varied widely around the world.Some areas that are ecologically very suitable for food production did not learn food production at all in prehistory, although some areas of prehistoric food production were in their vicinity.The most obvious examples in this regard are the failure of agriculture and animal husbandry to spread to Indian-inhabited California from the American Southwest, and the failure to spread to Australia from New Guinea and Indonesia; the failure of agriculture to spread to South Africa from Natal Province in South Africa Cape of Good Hope Province.Even among all those areas where food production spread in prehistoric times, the rate and age of spread varied widely.At one end is the rapid spread of food production along an east-west axis: westward from Southwest Asia into Europe and Egypt, eastward into the Indus Valley (average rate of about 0.7 miles per year); eastward from the Philippines into Polynesia (3.2 miles per year) .At the other end is the slow spread of food production along a north-south axis: from Mexico northward into the American Southwest at a rate of less than 0.5 miles per year; corn and beans spread northward from Mexico at a rate of less than 0.3 miles per year, Became a prolific crop in the eastern United States around 900 AD; llamas traveled north from Peru to Ecuador at a rate of less than 0.2 miles per year.If maize had not been domesticated as late as 3500 BC, as my conservative estimates in the past and some archaeologists now assume, but as most archaeologists used to assume (and many of them still do), Assumed), the age of maize domestication was much earlier, so the above difference may be even larger.

There are also huge differences in whether complete sets of crops and livestock are spread, again implying that barriers to spread are stronger or weaker.For example, while most of Southwest Asia's founder crops and livestock did spread westward to Europe and eastward to the Indus Valley, domesticated mammals in the Andes (llama/alpaca and prototheca) were pre-Columbian None have ever reached Central America.This astonishing lack of transmission urgently needs to be explained.After all, Mesoamerica already had dense agricultural populations and complex societies, so there is little doubt that Andean domestic animals, if they existed, were probably an important source of meat, transportation, and wool.However, with the exception of dogs, Mesoamerica has absolutely no native mammals to meet these needs.However, some South American crops managed to reach Central America, such as cassava, sweet potatoes and peanuts.What selective barrier lets these crops through, but screens out llamas and rats?

There is a more ingenious term for this geographical difference in the difficulty of species transmission, which is called the phenomenon of preemptive domestication.Most wild plants that later become our crops vary genetically from place to place because different genetic mutants have been established in wild ancestral populations in different regions.Likewise, the changes required to turn wild plants into crops could in principle be brought about by different new mutations into different selection processes that produce the same result.From this, one can look at a certain crop that was widespread in prehistoric times, and ask whether all its varieties show the same wild mutation or the same transforming mutation.The object of this investigation is to determine whether the crop has developed in one area or independently in several areas.

If such genetic analyzes were performed on ancient staple crops from the New World, many of them turned out to include two or more different wild varieties, or two or more different transformed mutants.This suggests that the crop was domesticated independently in at least two different regions, and that some varieties of the crop inherited mutations specific to one region, while other varieties of the same crop inherited mutations specific to the other region mutation.On this rationale, some botanists have concluded that lima beans, kidney beans, and peppers were all domesticated on at least two separate occasions, once in Mesoamerica and once in South America; It has also been independently domesticated at least twice, once in Central America and once in the eastern United States.In contrast, most ancient crops in Southwest Asia show only one different wild variety or different transformed mutants, suggesting that all modern varieties of the crop originated from just one domestication.

What would it mean if the crop was domesticated repeatedly and independently in several different areas of its wild range, rather than just once and in one area?We have seen that domestication of plants is the modification of wild plants so that they are beneficial to humans by virtue of larger seeds, less bitterness, or other qualities.Thus, if a productive crop already existed, early farmers would have grown it rather than re-domesticated from scratch by collecting its not-so-useful wild relatives.Evidence for just one domestication suggests that once a wild plant was domesticated, the crop spread rapidly to other areas throughout the wild plant's range, preempting the need for independent domestication of the same plant in other areas.However, if we find evidence that wild ancestors of the same plant were domesticated independently in different areas, we can infer that the crop spread too slowly to preempt domestication of the plant elsewhere.Evidence for mainly one-off domestication in Southwest Asia and frequent multiple domestication in the Americas may thus provide more subtle evidence that crops spread more easily in Southwest Asia than in the Americas.

The rapid spread of a crop may have preempted not only the domestication of the same plant's wild ancestor somewhere else, but also the domestication of related wild plants.If the pea you grow is already a good variety, it is of course pointless to domesticate the wild ancestor of the same kind of pea from scratch, but it is also pointless to domesticate the close relatives of the vetch variety, because it would be of no use to farmers. As far as we are concerned, this pea and the domesticated pea are actually the same thing.The ancestor crops of all Southwest Asia preempted the domestication of any plant relatives throughout the vast area of ​​western Eurasia.In contrast, in the New World there are many examples of equally important, closely related yet distinct plants domesticated in Central and South America.For example, 95 percent of the cotton grown in the world today belongs to the short-staple cotton that was domesticated in Mesoamerica in prehistoric times.However, it was Barbados cotton that prehistoric South American farmers grew.Apparently, the difficulty of getting cotton from Mesoamerica to South America prevented it from preemptively preventing the domestication of different varieties of cotton there (and vice versa) in prehistoric times.Peppers, squash, amaranth, and Chenopodiaceae are other crops of which different but related varieties were domesticated in Central and South America, since none spread quickly enough to preempt prevent the domestication of other species.

So many different phenomena boiled down to the same conclusion: food production spread out faster from Southwest Asia than in the Americas, and probably faster than in sub-Saharan Africa as well.These phenomena include: the complete failure of food production to reach some areas where ecological conditions are suitable for food production; differences in the speed and selectivity of the spread of food production; and whether the earliest domesticated crops preempted the re-domestication of the same plants Or there are differences in the domestication of close relatives.How is it that the spread of food production was more difficult in the Americas and Africa than in Eurasia?

To answer this question, let's first look at the rapid spread of food production out of Southwest Asia (the Fertile Crescent).Shortly after food production arose there, slightly earlier than 8000 B.C., a wave of food production spreading outward from the center occurred in western Eurasia and elsewhere in North Africa, spreading both east and west, away from the crescent Fertile land is getting further and further away.On this page I have drawn a detailed map (Figure 10.2) compiled by the geneticist Daniel Zohli and the botanist Maria Hopf, which they use to illustrate the wave of food production that reached Greece by 6500 BC, Cyprus and the Indian subcontinent, Egypt shortly after 6000 BCE, central Europe by 5400 BCE, southern Spain by 5200 BCE, and Britain by around 3500 BCE.In each of these regions, food production was initiated by certain crops and livestock from the same group of plants and animals that were first domesticated in the Fertile Crescent.In addition, the Fertile Crescent crops and herds entered Africa at some still uncertain date, traveling south to Ethiopia.However, Ethiopia also developed many indigenous crops, and we do not yet know whether these or successive crops introduced from the Fertile Crescent pioneered food production in Ethiopia.

Of course, not all of these crops and livestock spread to those remote areas.Egypt, for example, was too warm for einkorn wheat to settle there.In some remote areas some of this whole crop and livestock were introduced at different times.In southwestern Europe, for example, sheep were introduced earlier than cereals.Some remote areas also embarked on the domestication of several native crops, such as the poppy in western Europe and possibly the watermelon in Egypt.But much of the food production in the backcountry initially relied on plants and animals domesticated in the Fertile Crescent.These domesticated plants and animals were followed by other inventions originating in or near the Fertile Crescent, including the wheel, writing, metalworking, milking, fruit growing, and the brewing of beer and wine. Why did this crop of plants start food production all over western Eurasia?Was it because there were a number of such wild plants in as many areas, where they were found as useful as in the Fertile Crescent, and were domesticated independently?No, not for this reason.First, many of the Fertile Crescent's founder crops didn't even originally grow wild outside Southwest Asia.For example, of the 8 major founder crops, with the exception of barley, none were wild in Egypt.Egypt's Nile River Valley provided a setting similar to the Fertile Crescent's Tigris and Euphrates River Valleys.Thus, the crops that grew well in the Mesopotamia also did well in the Nile Valley, leading to the dramatic rise of native Egyptian civilization.But the grain which gave rise to this remarkable rise of Egyptian civilization was not originally available in Egypt.The people who built the sphinxes and the pyramids ate crops native to the Fertile Crescent, not Egypt. Second, even if wild ancestors of these crops did occur outside Southwest Asia, we can be sure that European and Indian crops were largely derived from Southwest Asia rather than locally domesticated.For example, wild flax occurs westward in Britain and Algeria, eastward along the Caspian Sea coast, and wild barley even eastward in Tibet.However, in the case of most of the Fertile Crescent's founder crops, all the cultivated varieties in the world today have only one arrangement of chromosomes, while their wild ancestors have multiple arrangements of chromosomes; A mutation (from many possible mutations) by which bred breeds are distinguished from their wild ancestors by some characteristic desirable to humans.All cultivated peas, for example, share the same recessive gene that prevents the mature pods of cultivated peas from bursting naturally, like vetch pods, and spilling the peas on the ground. Clearly, most of the Fertile Crescent founder crops were not re-domesticated elsewhere after they were initially domesticated in the Fertile Crescent.If they were domesticated multiple times independently, different arrangements of their chromosomes or different mutations would show the legacy of this multiple origin.These are therefore typical examples of the phenomenon of preemptive domestication that we discussed earlier.The rapid spread of the Fertile Crescent crops preempted any other possible attempts to domesticate the same wild ancestor within the Fertile Crescent or elsewhere.Once the crop is available, there is no need to collect it from the wild to make it domesticated again. In the Fertile Crescent and elsewhere, the ancestors of most founder crops had wild relatives that were likely also suitable for domestication.The pea, for example, is a plant in the genus Pisum, a genus that includes two wild species: the former domesticated into our garden peas, and the yellow pea, which was never domesticated.However, wild yellow peas taste great both fresh and dried, and are widely available in the wild.Likewise, wheat, barley, lentils, chickpeas, beans, and flax all have many wild relatives in addition to the domesticated varieties.Some of these related bean and barley-like crops were in fact domesticated independently in the Americas or China, far from their earlier domestication sites in the Fertile Crescent.But in western Eurasia, only one of the several potentially valuable wild species was domesticated—probably because this one spread so quickly that people stopped collecting other wild relatives and kept only This crop is for food.Again, as we discussed earlier, the rapid spread of the crop preempted not only attempts to domesticate its wild ancestors, but also any attempts that might have been made to further domesticate its relatives. Why did crops spread outward from the Fertile Crescent so quickly?The answer depends in part on the east-west axis of Eurasia that I spoke of at the beginning of this chapter.At the same latitude, the length of the day and the change of seasons are exactly the same.To a lesser extent, they also tend to share similar diseases, temperature and rainfall regimes, and plant and animal habitats or biome areas (vegetation types).For example, Portugal, northern Iran, and Japan are about the same latitude, 4,000 miles east and west of each other, but they are all similar in climate, and their climates are different from those just 1,000 miles due south. difference.On each continent, habitats of the so-called tropical rainforest type lie within about 10 degrees south and north of the equator, while low jungle habitats of the Mediterranean type (such as those of California and European scrublands) ) is between about 30° and 40° north latitude. However, the germination, growth and disease resistance of plants are fully adapted to these climatic characteristics.Seasonal changes in day length, temperature, and rainfall act as signals for seed germination, seedling growth, and mature plants to flower, set, and bear fruit.Each plant population is genetically programmed by natural selection to respond appropriately to the signals of the seasonal situation in which it evolves.This seasonal pattern varies greatly with latitude.For example, at the equator the length of the day is constant throughout the year, but in temperate regions the day gradually gets longer as time progresses from the winter solstice to the summer solstice, and then gradually gets shorter throughout the second half of the year.The growing season—the period of time when the temperature and day length are suitable for plants to grow—is shortest at southern latitudes and longest near the equator.Plants are also adapted to the diseases prevalent in their regions. Woe to plants whose genetic arrangement does not match the latitude of the area in which they are grown!Imagine what would happen to a Canadian farmer if he was so foolish as to plant a corn suitable for growing far south in Mexico.The corn, which was genetically programmed to grow in Mexico, should be ready to germinate in March, only to find itself still buried under 10 feet of snow.If the corn had been genetically rearranged so that it germinated at a more Canadian time -- say late in June -- it would still be in trouble for other reasons.Its genes tell it to grow unhurriedly, as long as it reaches maturity in five months.This is a perfectly safe practice in Mexico's temperate climate, but a disastrous one in Canada, as it guarantees that the corn will be killed by the autumn frost before it can grow any mature cobs.The corn would also lack genes for resistance to diseases in northern climates and carry genes for resistance to diseases in southern climates.All these features make it difficult for plants at lower latitudes to adapt to conditions at southern latitudes, and vice versa.As a result, most Fertile Crescent crops grow well in France and Japan, but poorly at the equator. Animals, too, are able to adapt to climate characteristics related to latitude.We are typical animals in this respect, as we know through introspection.Some of us can't stand the cold northern winters, the short days and unique germs, while others can't stand the hot tropical climate and its unique germs.In recent centuries, settlers from the cool northern regions of Europe have preferred to move to the equally cool climates of North America, Australia, and South Africa, while in the equatorial countries of Kenya and New Guinea they have preferred to live in the cool highlands.Nordics sent to the hot tropics of the lowlands used to die en masse from diseases such as malaria, against which the inhabitants of the tropics had developed some natural resistance. That's part of the reason Fertile Crescent domesticated plants and animals spread east and west so quickly: They've adapted so well to the climates of the regions in which they spread.For example, agriculture spread rapidly across the Hungarian plain into Central Europe around 5400 B.C., so that the earliest peasant sites (marked by characteristic lined pottery) in a vast area from Poland westward to the Netherlands were almost simultaneously existing.By A.D. 1, grains native to the Fertile Crescent were cultivated over a 8,000-mile stretch from the Atlantic coast of Ireland to the Pacific coast of Japan.This east-west expanse of Eurasia is the largest landmass distance on Earth. Thus, the east-west axis of Eurasia allowed Fertile Crescent crops to rapidly initiate agriculture in temperate regions from Ireland to the Indus Valley and enrich the independent emergence of agriculture in eastern Asia.Conversely, crops that were first domesticated in areas far from the Fertile Crescent but at the same latitude were able to make their way back to the Fertile Crescent.Today, when seeds are transported around the world by boat and plane, we take for granted that our meals are a geographical hodgepodge.A typical meal at an American fast food restaurant might consist of chicken (first domesticated in China) and potatoes (from the Andes) or corn (from Mexico), seasoned with black pepper (from India), and served with a cup of coffee (from the native Ethiopia) to aid digestion.However, no later than 2,000 years ago, the Romans also supported themselves on a hodgepodge of food, mostly produced elsewhere.Among the crops of the Romans, only oats and poppies were native to Italy.The staple diet of the Romans was a group of founder crops from the Fertile Crescent, plus umbo (native to the Caucasus Mountains), millet and dill (domesticated in Central Asia), cucumbers, sesame and citrus (from India), and Chicken, rice, apricot, peach and millet (native to China).Although Roman apples were indigenous to at least western Eurasia, they were grown with the help of grafting techniques developed in China and spread westward from there. While Eurasia has the world's largest landmass at the same latitude, and thus provides the most dramatic example of the rapid spread of domesticated plants and animals, there are others.Comparable in dispersal rate to the Fertile Crescent bulk crop was the eastward dispersal of a subtropical crop initially concentrated in southern China, with additional new additions reaching tropical Southeast Asia, the Philippines, Indonesia, and New Guinea. crops.Within 1,600 years, the resulting crop—including bananas, yams, and yams—had spread more than 5,000 miles east, into the tropical Pacific, and finally to the Polynesian islands.Another plausible example is the spread of crops from east to west within Africa's vast Sahel belt, but paleobotanists still need to work out the details. The ease with which domesticated plants spread east-west across Eurasia can be contrasted with the difficulty with which they spread along the north-south axis in Africa.Most of the founder crops of the Fertile Crescent reached Egypt quickly, and then spread south until the cooler Ethiopian highlands, where their spread ended.South Africa's Mediterranean-type climate should be ideal for these crops, but the 2,000 miles of tropical surroundings between Ethiopia and South Africa present an insurmountable barrier.African agriculture in sub-Saharan Africa began with the domestication of native wild plants in the Sahel and tropical West Africa, such as sorghum and African yam, which had adapted to the warm climate, constant summer rainfall and Relatively constant length of day. Similarly, southward crossings of domestic animals in the Fertile Crescent through Africa were halted or slowed by climate and disease, notably tsetse-borne trypanosomiasis.The horses never went further than some West African kingdoms north of the equator.In the mid-2000s, cattle, sheep, and goats stagnated on the northern edge of the Serengeti plains, while new human economies and livestock breeds continued to develop.Cattle, sheep, and goats did not finally reach South Africa until the period between AD 1 and AD 200, some 8,000 years after domestication of livestock in the Fertile Crescent.Tropical African crops also had difficulty spreading southward in Africa, arriving in South Africa with black African farmers (Bantu) only after the introduction of those Fertile Crescent livestock.However, these tropical African crops were not able to spread across the Fish River in South Africa because the Mediterranean-type climate to which they were not adapted prevented their progress. This outcome is a very familiar process in the past 2,000 years of South African history.South Africa's indigenous Khoisan people (also known as Hottentots and Bushmen) have some livestock, but still no agriculture.They were outnumbered and replaced by black African farmers northeast of the Fish River, but their southward expansion also ended at the Fish River.Only when European settlers arrived by sea in 1652, bringing with them crops from the Fertile Crescent, did agriculture flourish in South Africa's Mediterranean-type climate.The conflict between all these peoples has caused some of the tragedies of modern South Africa: the rapid mass death of the Khoisan by European germs and guns; a century-long series of wars between Europeans and blacks; another century of racial oppression; now Europeans and blacks are making efforts to find a new mode of coexistence in the lands of the Khoisan of yore. The ease with which domesticated plants spread across Eurasia can also be contrasted with the difficulty with which they spread along the north-south axis of the Americas.The distance between Central and South America—for example, between the highlands of Mexico and the highlands of Ecuador—is only 1,200 miles, about the distance between the Balkans and Mesopotamia in Eurasia.The Balkans provided the ideal growing environment for most Mesopotamian crops and livestock, and received the Fertile Crescent domesticated flora and fauna in less than 2,000 years.This rapid spread preempted the opportunity to domesticate those plants, animals, and related species.The Mexican highlands and the Andes should also be suitable growing environments for many of each other's crops and livestock.Several crops, notably Mexican maize, did spread to another area before the time of Columbus. But some other crops and livestock failed to spread between Central and South America.The cool highlands of Mexico would have been ideal for raising llamas, guinea pigs and growing potatoes, all of which were domesticated in the cool highlands of the South American Andes.However, the northward spread of these Andean specialties was completely blocked by the hot lowlands of Central America in between.Five thousand years after llamas were domesticated in the Andes, the Olmec, Mayan, Aztec, and all other indigenous societies in Mexico still had no pack animals, and none of them except dogs. Domesticated mammals that are eaten. Conversely, turkeys domesticated in Mexico and sunflowers grown in the eastern United States would have thrived in the Andes, but their southward spread was blocked by the intervening tropical climate.That 700-mile north-south distance alone keeps Mexican corn, squash, and legumes from reaching the southwestern United States thousands of years after they were domesticated in Mexico, and Mexican peppers and Chenopodiaceae never reached them in prehistoric times. reach there.In the millennia after maize was domesticated in Mexico, it failed to spread north into eastern North America because of the generally cooler climate and shorter growing season there.Sometime between A.D. 1 and 200, corn finally appeared in the eastern United States, but as a very minor crop.It wasn't until around AD 900, after hardy varieties of maize were bred for northern climates, that maize-based agriculture was able to contribute to the Mississippi culture, the most complex Native American society in North America, but this prosperity was short-lived. It died of the germs brought by the Europeans who came with Columbus and who came after him. It will be recalled that, based on genetic studies, most of the Fertile Crescent crops turned out to be the product of only one domestication process, which produced crops that spread quickly and preempted any other early domestication of the same or related species of plants .In contrast, many apparently widespread Indian crops contain relatives, or even genetically varied varieties of the same species, all found in Central and South America and the eastern United States independently domesticated.Regionally, closely related species succeed each other in amaranth, legume, ricaceae, pepper, cotton, squash, and tobacco.In green beans, lima beans, chili peppers, and gourds, different varieties of the same variety succeed each other.This outcome of multiple independent domestications may provide further evidence of the slow spread of crops along the north-south axis of the Americas. Thus, the two largest continental masses, Africa and America, with their axes running mainly north-south, had the effect of a slow spread of crops.In some other parts of the world, the slow north-south spread has significant effects only on a smaller scale.Other examples of this include the very slow exchange of crops between the Indus Valley of Pakistan and South India, the slow spread of food production in South China to West Malaysia, and the failure of food production in tropical Indonesia and New Guinea to separate in prehistoric times. Arrive in the modern farmlands of South West and South East Australia.These two corners of Australia are now the continent's breadbasket, but they lie more than 2,000 miles south of the equator.Agriculture there had to wait until crops adapted to Europe's cooler climate and shorter growing season arrived from far away Europe on European ships. I have been emphasizing latitude, which can be easily determined on a map at a glance, because it is a major determinant of climate, growing environment, and ease of spread of food production.However, latitude is of course not the only determining factor, and it is not always true to say that adjacent areas at the same latitude have the same climate (although they do not necessarily have the same length of day).Topographical and ecological boundaries are much more pronounced on some continents than on others, creating locally significant barriers to crop dispersal. For example, although the southeastern and southwestern United States lie at the same latitude, crop dispersal between these two regions was very slow and selective.This is because a large part of Texas and the southern Great Plains across the middle are dry and unsuitable for agriculture.There is also a consistent example in Eurasia of the eastward spread of Fertile Crescent crops.The crops quickly spread west to the Atlantic Ocean and east to the Indus Valley without encountering any major obstacles.However, further east in India, the expansion of agriculture involving different crops and farming techniques to the Gangetic plains of northeastern India was greatly delayed by a shift from predominantly winter to predominantly summer rainfall.To the east, there are Central Asian deserts, the Tibetan plateau, and the Himalayas that together separate the temperate regions of China from the western regions of Eurasia with a similar climate.Thus, the early development of food production in China was independent of that of the Fertile Crescent at the same latitude, and resulted in some entirely different crops.Yet even these barriers between China and western Eurasia were at least partially overcome when wheat, barley, and horses from West Asia arrived in China in 2000 BC. Moreover, the resistance to this north-south transfer of 2,000 miles will vary widely according to local conditions.Fertile Crescent food production spread over such long distances to Ethiopia, while Bantu food production spread rapidly southward from the Great Lakes region of Africa to Natal province because, in both cases, the intervening The regions have similar rainfall regimes and are therefore suitable for agriculture.By contrast, the spread of the crop southward from Indonesia to southwestern Australia would have been entirely impossible, and the much shorter distance from Mexico to the southwestern and southeastern United States would have been hindered by the intervening Agriculture is slow in desert areas.The absence of a plateau in Mesoamerica south of Guatemala, and the extreme narrowness of Mesoamerica south of Mexico, especially Panama, were at least as important as latitudinal gradients in hindering the exchange of crops and livestock between the Mexican plateau region and the Andes region. Differences in the orientation of continental axes affected not only the spread of food production, but also the spread of other technologies and inventions.例如，公元前3000年左右在西南亚或其附近发明的轮子，不到几百年就从东到西迅速传到了欧亚大陆的很大一部分地区，而在史前时代墨西哥独立发明的轮子却未能传到南面的安第斯山脉地区。同样，不迟于公元前1500年在新月沃地西部发展起来的字母文字的原理，在大约1000年之内向西传到了迦太基，向东传到了印度次大陆，但在史前时期即已盛行的中美洲书写系统，经过了至少2000年时间还没有到达安第斯山脉。 当然，轮子和文字不像作物那样同纬度和白天长度有直接关系。相反，这种关系是间接的，主要是通过粮食生产系统及其影响来实现的。最早的轮子是用来运输农产品的牛拉大车的一部分。早期的文字只限于由生产粮食的农民养活的上层人士使用，是为在经济上和体制上都很复杂的粮食生产社会的目的服务的（如对王室的宣传、存货清单的开列和官方记录的保存）。一般说来，对作物、牲畜以及与粮食生产有关的技术进行频繁交流的社会，更有可能也从事其他方面的交流。 美国的爱国歌曲（美丽的亚美利加）说到了从大海到闪光的大海，我们的辽阔的天空，我们的琥珀色的谷浪。其实，这首歌把地理的实际情况弄反了。和在非洲一样，美洲本地的作物和牲畜的传播速度由于狭窄的天空和环境的障碍而变得缓慢了。从北美大西洋岸到太平洋岸，从加拿大到巴塔哥尼亚高原，或者从埃及到南非，看不见本地绵延不断的谷浪，而琥珀色的麦浪倒是在欧亚大陆辽阔的天空下从大西洋一直延伸到太平洋。同美洲本地和撤哈拉沙漠以南非洲的农业传播速度相比，欧亚大陆农业的更快的传播速度在对欧亚大陆的文字、冶金、技术和帝国的更快传播方面发挥了作用。 提出所有这些差异，并不就是说分布很广的作物是值得赞美的，也不是说这些差异证明了欧亚大陆早期农民具有过人的智慧。这些差异只是反映了欧亚大陆轴线走向与美洲或非洲大陆轴线相比较的结果。历史的命运就是围绕这些轴线旋转的。

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Notes: