FIFTH STAGE OF THE HISTORY. 



The squirrel shrew {Tupaia chrysura), probably not 

 widely different from its ancestor which gave rise to 

 the lemuroids and thereby to the primates. The 

 arboreal life of this creature undoubtedly had an 

 important part in fitting it to progress upward, since 

 it allowed the senses of sight, touch and hearing to be 

 developed equably, and removed the animal from 

 the fierce competition going on among larger mam- 

 mals on the ground below him. These changes in 

 habit were accompanied by changes in the structure 

 of the brain, which made further evolution possible. 



Even as far back as this stage in man's history, the 

 beginning of the use of the fore-feet as hands is seen, 

 as it is with the common squirrels, for the tree- 

 shrews often sit on their hind legs and hold their food 

 in their forepaws. They are largely insectivorous, 

 and are agile, active creatures. The life in the trees 

 of man's ancestors at a similar stage undoubtedly 

 tended to develop this agility and quickness of move- 

 ment which depends on the coordination of many 

 muscles; and natural selection weeded out those 

 who did not show progress along the chosen line. 

 Thus the growth of the powers of the brain, which 

 has largely contributed to make man the dominant 

 mammal, received an impetus from the arboreal life 

 of his ancestors, the importance of which it is difficult 

 to overestimate. Photograph from the Brooklyn 

 Institute of Arts and vSciences. (Fig. 4.) 



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flr.viv 



385 



