THE DONKEY'S ANCESTORS. 195 



every advance in structure through tertiary 

 times, not only absolutely as the whole 

 animal grows bigger, but relatively also in 

 proportion to the other parts. Indeed, there 

 has been a regular increase in intelligence 

 and brain-power among all the mammalia 

 from the moment of their first appearance 

 upon the earth till the present time. 



Such an increase naturally results from 

 the very conditions of evolution. Not only 

 the strongest and the physically best adapted 

 have survived in the long run, but the 

 cleverest and the shiftiest as well. All very 

 early mammals, discovered sparsely in the 

 secondary formations, have extremely small 

 and ill-developed brains. All surviving 

 isolated archaic forms, preserved in special 

 and long insulated areas, far from the fierce 

 competition of higher types, as is the case 

 with the marsupials of Australia, the low 

 lemuroid animals of Madagascar, and the 

 edentates of South America, have brains 

 hardly better than these primitive species. 



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