AND ITS INHABITANTS 137 



expansion of grazing forms — horses, camels, deer — and the 

 restriction and often the extinction of browsing types. It is 

 true that browsing forms are still extant, but not in their old 

 profusion nor In their old homes, while the grazing forms are 

 numerous and characteristic of the widespread steppes the 

 world over. 



Origin of man. We have observed the influence of geologic 



I change in the evolution of the brute, and we have now to 

 inquire whether mankind in his long upward course has been 

 amenable to those same laws or whether he has been a thing 

 apart from other forms of life, whose development has been 

 controlled by other Influences. As the primates, the group to 

 which mankind belongs, are to be classed with the modernized 

 mammals, their course of evolution up to the point of their 

 differentiation as primates must have been one with all the 

 rest and hence the result of the same chain of causes. And 

 their differentiation from the other mammals when they came 

 to the parting of the ways seems to have been due to the de- 

 parture of the latter from their primal mode of life and 

 structure rather than to any special evolution of the primates 

 themselves, for In many ways they are among the most primi- 

 tive of the modernized hosts, and their tree habitations may 

 well have been a very ancient habitat of the whole mammalian 

 race.^ 



They throve In their northern home just as did their other 

 compatriots, and like them drove southward along the several 

 continental radii, the rear guard drawing in toward the equator 

 with the northern limits of the tropical forests within which 

 they dwelt and upon which, with rare exceptions, they are 

 dependent to this day for food and safety. They reached 

 North America, as the map (Fig. 27) Indicates, early in 

 Eocene time (Wasatch) and became so abundant as to form a 



8 Matthew, W^. D., "The Arboreal Ancestry of the Mammalia." Amer. NaU, 

 vol. 38, 1904, pp. 811-818. 



