The Great Divide

varying strength of the monsoon and its temporal relation to the emergence (and subsequent collapse) of Old World civilisations was described in chapter five. All we need add here is that, given the domestication of cereal grasses in the Old World at about 10,000 years ago, the major environmental/ideological issue in Eurasia over that time has been fertility . The landmass, bit by bit, has been drying.
    In the New World, on the other hand, the major factor affecting weather has been the increasing frequency of enso, from a few times a century about six thousand years ago, to every few years now. Besides the occurrences of enso itself, its relationship with volcanic activity, given the make-up of the Pacific Ocean (an enormous body of water over a relatively thin crust), also appears to have been important. We saw in chapter five that Meso- and South America are the most volcanically active mainland areas of the world where major civilisations have formed. Put all this together and the most important environmental issue in the Americas over the past few thousand years, which has had fundamental ideological consequences, has been the increasing frequency of destructive weather .
    We cannot say with certainty that these differences were definitive, or that they ultimately account for the systematic ideological variations we shall be discussing shortly. We have already noted that in our natural experiment there are too many variables to satisfy purists. What we can say is that these systematic differences in climate across the hemispheres dovetail plausibly with the historical patterns that are observable between the New World and the Old World and to that extent may help us understand the different trajectories.
    H OW AND W HY THE G ODS S MILED ON THE O LD W ORLD
    After the geographical and climatological factors that determined basic and long-term differences between the two hemispheres, the next most important factors lay in the realm of biology – plants and animals. In the plants realm, we may say that, again, there were two main differences between the hemispheres. The first concerned cereals: grain. In Eurasia in particuar there was a naturally occurring range of grasses – wheat, barley, rye, millet, sorghum, rice – susceptible of domestication and, because of the east-west configuration of the landmass, they were able to spread relatively rapidly once domestication was achieved. Surpluses were therefore built up relatively quickly and it was on this basis that civilisations were able to form. In the New World, on the other hand, what turned out to be the most useful grain there was evolved from teosinte which, in the wild, was, morphologically speaking, far more distant from the domesticated form than was the case with the Old World grasses. Furthermore, as we now know, because of its high sugar content (as a tropical rather than a temperate plant), maize was first used for its psychoactive properties rather than as a foodstuff. On top of everything else, maize – even when it did become a foodstuff – found it harder to spread in the New World because of the north-south configuration of the landmass, which meant that mean temperatures, rainfall and sunlight varied far more than they did in Eurasia. For this reason, the development of maize surpluses was much harder – and slower – to build up. As noted, possibly only Cahokia followed an Old World trajectory at all closely. Thus the domestication trajectory of the most important New World grain was very different from its more numerous counterparts in the Old World.
    The second crucial area where plants differed between the Old World and the New was in the realm of hallucinogens. The influence of these plants on history has perhaps not been appreciated before to this extent, but it is now clear that the distribution of psychoactive plants across the world is curiously anomalous. The figures, as we saw in chapter twelve, are that between 80 and 100 hallucinogenic species occur naturally in the New World, compared with not more than eight or ten in the Old World.
    It is also now clear that hallucinogens played a large and vital role in the religious thought of the New World but especially so in Central and South America, where the most advanced civilisations evolved.
    The role and effect of hallucinogens was essentially two-fold. First, they made the religious experience in the Americas much more vivid than in the Old World. Second, because of their