Contrast also the ease of east-west dif- 

 fusion in Eurasia with the difficulties of 

 diffusion along the Americas' north-south 

 axis. The cool highlands of Mexico would 

 have provided ideal conditions for raising 

 llamas, guinea pigs, and potatoes, all do- 

 mesticated in the cool highlands of South 

 America. But the northward spread of 

 those Andean species was stopped com- 

 pletely by the hot intervening lowlands of 

 Central America. As a result, the Olmec, 

 Maya, Aztec, and all other native civiliza- 

 tions of Mexico remained without pack 

 animals and without any edible domesti- 

 cated mammals except for dogs. 



Similarly, domesticated turkeys or sun- 

 flowers of North America might have 

 thrived in the Andes, but their southward 

 spread was also stopped at the tropics. For 

 thousands of years after com was domesti- 

 cated in Mexico, it was unable to spread 

 farther north because of the relatively cool 

 climates and shorter growing season. 

 About the time of Christ, com finally took 

 root in what is now the eastern United 

 States, but initially only as a very minor 

 crop. Not until a.d. 800, when a hardy va- 

 riety of com adapted to northern climates 

 was developed, did this grain finally trig- 

 ger the flowering of the most complex Na- 

 tive American society of North America, 

 the Mississippian culture — just in time for 

 it to be decimated by European-introduced 

 germs. 



In contrast to the single Fertile Crescent 

 origin that Zohary and Hopf trace for most 

 widespread Eurasian crops, many appar- 

 ently widespread Native American crops 

 prove, on closer examination, to consist of 

 distinct varieties or related species, inde- 

 pendently domesticated in Mesoamerica 

 and South America. That's tme, for ex- 

 ample, of American cotton, beans, lima 

 beans, chili peppers, and squashes. While 

 Fertile Crescent crops spread rapidly and 

 preempted other incipient developments 

 of domestication, slow diffusion and many 

 independent domestications were the mle 

 in the Americas. 



Slower development of Native Ameri- 

 can agriculture (compared with Old Worid 

 agriculture) contributed to the slower de- 

 velopment of Native American writing, 

 metallurgy, technology, shipping, and em- 

 pires. Those differences helped seal the 

 outcome of the collision between Native 

 Americans and European settlers that 

 began with Columbus. Yes, I acknowledge 

 other geographic and biological contribut- 

 ing factors as well. Humans colonized 

 Eurasia long before they colonized the 

 Americas. In addition, the Americas had 



few domesticable large wild animal spe- 

 cies, while in Europe many such animals 

 were used to pull plows or make cavalry 

 charges. Those domesticates harbored the 

 animal pathogens from which Eurasia's 

 most lethal weapon, human pathogens 

 such as the smallpox and measles vimses, 

 evolved. But the different orientations of 

 the continents' axes remain an immensely 

 important factor. 



In the United States, the patriotic song 

 "America the Beautiful" invokes our spa- 

 cious skies, our amber waves of grain. 

 Alas, that song reverses geographic reali- 

 ties. No waves of native grain ever 

 reached the Pacific coast of North Amer- 



ica, just as none ever stretched from Egypt 

 to South Africa, while amber waves of 

 wheat and barley did come to stretch 

 across the spacious skies of Eurasia. These 

 differences don't prove that widely distrib- 

 uted crops are admirable, nor do they tes- 

 tify to the superior ingenuity of early 

 Eurasian farmers. They reflect instead the 

 orientation of Eurasia's axis compared 

 with that of the Americas or of Africa. 

 Around those axes turned the fortunes of 

 history. 



Jared Diamond is a physiologist and evo- 

 lutionary biologist at the University of 

 California Medical School, Los Angeles. 



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