HUMAN ADAPTIBILITY TO HOT CONDITIONS OF DESERTS 



Dr. J. S. Weinor 

 (Oxford) 



The ten or so major hot desert regions — Sahara, Kalahari, Thar, Persian, Turan, 

 Gobi, Arabian, Mohave, Atacama, Argentinian — are of interest physiologically be- 

 cause of the combination of the following characteristics; the high air temperatures, 

 the high intensity of solar radiation, the occurrence of fierce hot winds, the low 

 humidity and the diurnal and seasonal fluctuations. Daytime dry bulb temperatures 

 in the shade may greatly exceed normal body temperature, maxima as high as 135°F 

 have been noted; mean daily maxima of 100°F and over occurring on 50 days or more 

 in the hot season, or of 95°F (i.e. very close to body temperature) on about 100 days, 

 are on record for the Sahara, Arabian, Colorado, Australian and Thar deserts. Such 

 temperatures imply not only the cessation of an appreciable convective heat loss 

 from the body but a large addition of heat to the body from the ambient surroundings ; 

 when winds prevail the convective heat load will be still further increased roughly 

 in proportion to the square root of the impinging air speed. Some gain of heat to 

 the body by conduction also occurs in the desert since surface temperatures of 

 150°F even 170°F may occur. Over and above these sources of desert heat there is 

 the high intensity of the sun's radiation, unhindered by atmospheric moisture and 

 added to by re- radiation from hot surfaces. The magnitude of the heat flow to the 

 body and its capacity for dealing with it are considered below. The physiological 

 severity of the desert depends on the intensity and duration of the daily hot spells 

 in the summer season and it is for such short exposures that most information is 

 available from physiological analysis. A certain amount of data has been obtained 

 at first hand by investigations in deserts. The most notable work is that of Adolph 

 (1947) and Dill (1938) in America and the more clinical work of Ladell (1944) and 

 Home & Mole (1950) in the Persian and Pakistan regions. The great bulk of our 

 data has been obtained in studies in artificially heated rooms. Nearly all these 

 studies give an insight into the effects of relatively short exposures but in few of 

 these have high radiant temperatures figured very much. Far less is known about 

 the effects of the extreme swings in temperature experienced in many desert areas 

 or of the cumulative effects over a season or a period of years. Some insight into 

 the nature of long-term effects is provided by a consideration of the physical charac- 

 teristics of the people indigenous to the desert. 



1. Ethnology 



Probably less than one per cent of the world's population endure desert climates. 

 Yet even this number and the variety of the peoples it represents furnishes obvious 

 evidence of the capacity of man as a species to. withstand the thermal rigours of such 

 environments. The principal hot arid regions provide an interesting ethnological 

 picture which can only be presented in outline here. The central Asiatic desert is 

 part of the territory of a mixed stock whose affinities become progressively more 

 Mongoloid as one passes across the Gobi, and increasingly Turki- Alpine in the 

 plains west of the Pamirs. In the Thar desert there is a complex of groups difficult 



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