One of the things you notice in talking to Latin Americanist historians about the work of celebrity biogeographer Jared Diamond is their almost visceral reaction to his two-dimensional view of history, particularly evident in the wildly successful Guns, Germs, and Steel (W. W. Norton, 1997). As a colleague observed, “He doesn’t understand that Latin American history plays out in three dimensions, not two,” and this allusion to John V. Murra’s notion of verticality could easily have been extended to n-dimensions. If you keep that in mind, Jonathan Amith’s ambitious and impressive account of the historical geography and ecology of the Iguala Valley in central Guerrero falls into place, down to the enigmatic title. Perhaps one should add that Amith’s argument is neither Diamond’s nor Murra’s, despite the fact some historical geographers in Mexico, such as Bernardo García Martínez, have observed that portions of Guerrero bear more than a passing resemblance to Murra’s well-known theory of ecological niches.The agricultural potential of the Iguala Valley, Amith observes, diminishes as one travels south because average rainfall declines while temperature rises. Consequently, population densities were higher in the north; this, combined with the proximity of markets in Taxco, Cuernavaca, and Mexico City, drove up relative land rents in the north. By 1750, this process had reached something of equilibrium, and with it, effected a transition from ranching to agriculture. As elsewhere in New Spain, the potential profitability of the grain trade attracted investment and further commercialization. At the same time, the absence of investment and markets in south-central Guerrero made for “bifurcated patterns of development into northern and southern regions . . . between the increasingly impoverished south-central jurisdictions of Tixtla and Chilapa and the richer Taxco and Iguala jurisdictions to the north” (pp. 68, 257). This divergence precipitated a complex series of struggles between colonists, indigenous village authorities, migrant peasants, and the colonial authorities that exacerbated, rather than mitigated, regional economic disparities. The late-colonial cacao boom between Guayaquil and New Spain through the port of Acapulco, for example, only served to increase the demand for mules and muleteers from the Iguala Valley and had important spillovers into the salt and cotton trades as well. Even “well-intentioned” policies, such as the establishment of the famous spinning school at Tixtla under the subdelegate Juan Antonio de Rivas, could not withstand the effects of outmigration to the Iguala Valley and came to naught. Throughout Amith’s account, there is a continuing emphasis on native agency and on “place making and place breaking” as something more than mere reaction to an alteration in relative prices. The analysis is firmly based on impressive archival research, much of it in previously neglected materials. Indeed, it is difficult not to admire a study in which even the activity of itinerant merchants is analyzed down to the level of individual journeys between such places as Tenancingo, Acapulco, and Tepecuacilco.The novelty of Amith’s effort lies in his argument that southern Guerrero’s unique system of exchange was not organized around a dominant market center but instead consisted of “a series of loosely articulated small markets strung together by petty trade in specialized production and endless webs of credit and debt,” or a “model of exchange over multiple sites of acquisition and sale” (pp. 360, 361). It suggests, albeit from a generally conventional anthropological perspective, that there is something wrong the neoclassical model that views exchange and arbitrage as essentially identical. Of course, there have been other efforts to bring such a perspective to colonial Mexico, particularly Enrique Semo’s Historia del capitalismo en México (Ediciones Era, 1973), which gets a footnote but deserves better. The question is, and always has been, whether market incentives alone were sufficient to organize commercial activity in New Spain, as Stanley Stein pointed out over a generation ago. You don’t necessarily qualify as, God forbid, a Marxist for asking. Despite what our colleagues in economics believe, the answer isn’t written in the axioms. As Woodrow Borah astutely observed, cotton was a tributary good before the arrival of the Spaniards because that was the only “efficient” way of bringing it to the highlands to be woven, especially in a world of nontrivial transportation costs and ethnic subjugation.Somewhere out there, a historically sophisticated economic history of colonial Mexico remains to be written. When it is, one suspects that books such as Amith’s — and others like it — will finally give us a “new” economic history worthy of the name.