14 INTRODUCTION 



Again, in closely allied species the contrast is not pronounced or convincing; 

 but by comparing members in the primate group standing phyieticaily 

 far apart from each other, the essential differences between them gather the 

 full force of their cvohitional significance. They leave no room to doubt that 

 a progressive functional development has gone hand in hand with impressive 

 evohitional modifications in the structure of the brain. 



Bonds of Kinship among the Primates 



No attempt has been made to arrange the species in exact serial order. 

 Such classification would be open to numerous objections. A brief panoramic 

 view of the primates may, however, disclose the Inroad bonds of kinship 

 which hnt: them together in the foremost place of the vertebrate phylum. 

 One feature in this panorama is especially noteworthy. There has been a 

 strong tendency among the vertebrates to take refuge in the trees, either 

 to escape predacious contemporaries or otherwise to foster the opportunity 

 to live. Its obvious purpose is to increase the measure of safety by extending 

 the radius of retreat and making ascent from the ground a real biological 

 advantage. 



modifications induced by tree-dwelling 



With the advent of the primates, this arboreal tendency was diverted 

 into still another channel. Here it took the turn of affording an almost com- 

 plete permanency of abode rather than a refuge in time of emergency. Such 

 a change to more or less permanent tree-dwelling could but induce far- 

 reaching modifications. Not only did this life create a new type of habitat; 

 it at once enforced a new mode of transit over the leafy highways of the 

 tree tops. In order to obtain proper adjustment for such transportation, both 

 hand and loot acquired the qualities of prehensile organs. Locomotion of this 

 kind eventuated in the development of quadrumanal characters, with the foot 



