Jared Diamond - Guns, Germs & Steel

CHAPTER 10
spacious skies and tilted axes

ON THE MAP OF THE WORLD ON PAGE 177 (FIGURE 10.) compare the shapes and orientations of the continents. You'll 1 struck by an obvious difference. The Americas span a much greater tance north-south (9,000 miles) than east-west: only 3,000 miles at widest, narrowing to a mere 40 miles at the Isthmus of Panama. That the major axis of the Americas is north-south. The same is also though to a less extreme degree, for Africa. In contrast, the major axis* Eurasia is east-west. What effect, if any, did those differences in the ork tation of the continents' axes have on human history?
This chapter will be about what I see as their enormous, son tragic, consequences. Axis orientations affected the rate of spread of and livestock, and possibly also of writing, wheels, and other inver That basic feature of geography thereby contributed heavily to the different experiences of Native Americans, Africans, and Eurasians in.) last 500 years.
food production's spread proves as crucial to understar geographic differences in the rise of guns, germs, and steel as did its orgins, which we considered in the preceding chapters. That's because, as

SPACIOUS SKIES AND TILTED AXES • 177

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, in some cases, as a result of migrations of farmers 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 production 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

I 7 8 • GUNS, GERMS, AND STEEL
American California from the U.S. Southwest or to reach Australia from New Guinea and Indonesia, and the failure of farming to spread front South Africa's Natal Province to South Africa's Cape. Even among alt those areas where food production did spread in the prehistoric era, the rates and dates of spread varied considerably. At the one extreme was itt-l rapid spread along east-west axes: from Southwest Asia both west Europe and Egypt and east to the Indus Valley (at an average rate of aboqff 0.7 miles per year); and from the Philippines east to Polynesia (at 3.21 per year). At the opposite extreme was its slow spread along nor axes: at less than 0.5 miles per year, from Mexico northward to the U.1 Southwest; at less than 0.3 miles per year, for corn and beans from ] northward to become productive in the eastern United States around, 900; and at 0.2 miles per year, for the llama from Peru north to j These differences could be even greater if corn was not domesticated i Mexico as late as 3500 b.c., as I assumed conservatively for these tions, and as some archaeologists now assume, but if it was instead * ticated considerably earlier, as most archaeologists used to assume (a many still do).
There were also great differences in the completeness with which! of crops and livestock spread, again implying stronger or weaker to their spreading. For instance, while most of Southwest Asia's fou crops and livestock did spread west to Europe and east to the Indus Va neither of the Andes' domestic mammals (the llama / alpaca and the | pig) ever reached Mesoamerica in pre-Columbian times. That astor failure cries out for explanation. After all, Mesoamerica did develop farming populations and complex societies, so there can be no doubt i Andean domestic animals (if they had been available) would have valuable for food, transport, and wool. Except for dogs, Mesoamerica '\ utterly without indigenous mammals to fill those needs. Some South ican crops nevertheless did succeed in reaching Mesoamerica, such as i ioc, sweet potatoes, and peanuts. What selective barrier let those through but screened out llamas and guinea pigs?
A subtler expression of this geographically varying ease of spread i|f phenomenon termed preemptive domestication. Most of the wild species from which our crops were derived vary genetically from : area, because alternative mutations had become established among; wild ancestral populations of different areas. Similarly, the required to transform wild plants into crops can in principle be

SPACIOUS SKIES AND TILTED AXES • I 7 9
t by alternative new mutations or alternative courses of selection to • Id equivalent results. In this light, one can examine a crop widespread historic times and ask whether all of its varieties show the same wild tation or same transforming mutation. The purpose of this examination 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 rops 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 (Phaseolus lunatus), common beans (Phaseolus vulgaris), and chili peppers of the Capsicum annuutn I 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 particular crop stem from only a single domestication.
What does it imply if the same crop has been repeatedly and independently domesticated in several different parts of its wild range, and not just once and in a single area? We have already seen that plant domestication 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 o e same plant. However, when we find evidence that the same wild ancestor was domesticated independently in different areas, we infer that e crop spread too slowly to preempt its domestication elsewhere. The evi ence for predominantly single domestications in Southwest Asia, but requent multiple domestications in the Americas, might thus provide