CLIMATE AND RACE — COON 291 



than the arms. The Nilotics and Somalis and Masai and other black- 

 skinned peoples of the Sahara, Sudan, and the Horn of Africa have 

 long skinny legs and long gracile necks; no case of adaptation to a 

 given environmental situation could be clearer. The same is true 

 of South Indians, Ceylonese Vedda, most Melanesians, and the 

 Australian aborigines of the desert, as well as of white Australians 

 from Queensland. The Bushman of the Kalahari is extremely slen- 

 der; of the inhabitants of the ximerican deserts information is 

 defective. At any rate, as far as we know, the deseit portion of 

 Allen's rule holds for man, for obvious reasons. The mechanism 

 of change is less obvious. 



The other end of Allen's rule applies to adaptation to cold. Naked 

 savages can live without much clothing in temperatures down to the 

 freezing point. Several technical experiments have been performed 

 on Australian aborigines sleeping naked in the desert 'when the night 

 temperature fell to the frost point ( Wulsin, 1948) . These people keep 

 rows of small fires burning and sleep between rows. Parts of their 

 skin surface becomes quite cold, others hot. They seem to be able to 

 absorb radiant heat from the fires on some parts of their skin surface 

 in all of which the venous blood is at a minimum. Thus they survive 

 until morning. In the daytime the air temperature rises rapidly. 



The Yaghans (Hooton, 1928 ; Wulsin, 1948) , canoe Indians of Tierra 

 del Fuego, paddle nearly naked in their boats in foggy channels, in 

 an environment where year-round temperatures hover above and 

 about the freezing point. Darwin saw a naked woman nurse a naked 

 baby while sleet melted on her body, and a gi-oup of Yaghans who drew 

 up to the outer glow of the explorers' fire sweated profusely. The 

 Ona, foot Indians of the plains on the northern part of the island, 

 wore guanaco skin robes and moccasins, and slept behind skin wind- 

 breaks in the snow. Tlie Chukchi of Siberia, who wear Eskimo-style 

 clothing, like to remove their shirts to cool off, and Bogoras saw 

 Chukchi women thrust lumps of snow between their breasts for the 

 same purpose. 



The mechanism of heat loss in cold conditions will explain this. 

 Wlien the environmental temperature falls the body stops sweating 

 at 83° F., and heat loss is accomplished wholly by radiation and con- 

 vection. Venous blood, which has been returning from the back of 

 the hand through superficial blood vessels on the arm, is rerouted; 

 vasoconstriction shuts off this road, and vasodilation opens alternate 

 channels through deep-lying veins which surround the artery. The 

 chilled venous blood returning to the heart cools the arterial blood, 

 so that it will have less heat to lose, and the heat gained by the venous 

 blood is carried to the heart. Thus heat loss through the hand and 



