OUR FACE FROM FISH TO MAN 



the reptiles and finally producing the primates, 

 which eventually gave rise to man. 



Thus the human face owes the fundamental plan 

 of its upper and lower jaws to the mammal-like 

 reptiles and earliest mammals in which these im- 

 provements were first worked out. 



OUR MASK -FACE BECOMES MOBILE 



The origin of the mammals is one of the most 

 dramatic incidents in the whole story of human 

 transformation from fish to man. The central 

 problems set for the mammal-like reptiles were to 

 speed up all their vital processes and to maintain 

 them at a relatively high level; also to resist the 

 extreme changes of temperature of the harsh, 

 highly variable climates then prevalent, when 

 periods of glaciation alternated with tropical heat. 

 Means had to be found to insulate the body in 

 slowly conducting substances so as to defy the 

 cold; on the other hand, to enable the body to cool 

 itself safely when over-heated. Reptiles have this 

 power to a limited degree but it is greatly enhanced 

 in the mammals. For this purpose many "basic 

 patents" had to be worked out in the heat- 

 conserving organs, in the circulation of body 



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