224 THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. 



and as to the prevalence of disease by the further assumption of chmatic changes such as 

 have been inferred in previous chapters, practically all the difficulties vanish. The Mayas, 

 on this supposition, lived in an envkorunent as favorable as any now found within the 

 tropics. They did not suffer greatly from tropical diseases because the physical conditions 

 were not favorable to the propagation of harmful species of mosquitoes. 



The sort of chmatic change which we have inferred would involve the following con- 

 ditions at the height of the Maya civihzation: In the first place, the dry season would 

 have been longer, more windy, and colder than at present. This would not have influenced 

 the coastal strip so much as the interior. Hence the coast may have had considerable 

 forests or at least dense jungle, and may have been feverish. Farther in the interior, 

 however, where the ruins are chiefly located, relatively dry conditions would have prevailed 

 like those of northern Yucatan to-day, save that the contrast of seasonal temperature 

 would have been greater. Thus the habitat of the malarial species of mosquitoes would 

 have been much reduced, and fevers would have been to a considerable extent relegated 

 to the coastal forests, which therefore would have had httle population. In addition to 

 this the enervating influence of climatic uniformity would have been somewhat reheved, 

 and agriculture of the intensive kind would have been possible in the Peten plain, just as 

 it is to-day in northern Yucatan. The areas of big jungle where life is excessively easy 

 so long as the population remains uncivihzed and comparatively scanty, but where intensive 

 agriculture is to-day difficult, would have been much reduced. Thus the Peten region, 

 being a fertile lowland, would have been a natural center of civilization. In other words, 

 the adoption of the climatic hypothesis does not lead us to abandon our hypotheses as to 

 racial character and disease. It merely removed from them certain demerits of improb- 

 abihty. It supplies the elements which the other hypotheses lack, and in addition it 

 possesses the strength of being supported by strong external evidence. 



In this last statement Hes the chief significance of the present chapter. Our climatic 

 hypothesis was framed, crudely at first, in Russian Turkestan and Persia; it was revised in 

 Chinese Turkestan and India; modified greatly by studies in Palestine and Asia Minor, 

 and confirmed apparently by the burial of Olympia, by the distribution of population in 

 Greece, and, so it seems, by what others describe in North Africa. It was further con- 

 firmed,' but again much modified, by ruins in the southwestern United States and by the 

 trees of California. Finally, it was appUed to the torrid zone in Yucatan and seemed to 

 fit the facts. Now it has been carried to another tropical region where a fuller test is 

 possible. Here again, down to such minute details as small fluvial terraces, it seems to 

 be in accordance with the facts. Doubtless it will be further modified; doubtless I have 

 ascribed to it some results really due to other causes, but that is an inevitable stage of a 

 new subject. The only question is, how far does the present theory harmonize with the 

 great body of facts by which it has been, or maj' in future, be tested? So far as it does, 

 we may tentatively accept it. So far as it does not, it must be revised. 



