142 EVOLUTION OF THE EARTH 



is, after all, a limited environment and the descent to the ter- 

 restrial habitat was as necessary to further evolution manwards 

 as was that older emergence upon land on the part of our 

 piscine ancestry. In the former case as in the latter, the actual 

 attainment of the terrestrial habitat is supposed to have been 

 forced by geologic change of a very similar character. The 

 presumption is that central Asia was the evolutionary center 

 of the anthropoids and so far as our records go this is borne 

 out by the fossils, the oldest of which are found in the Siwalik 

 Hills of northern India in rocks of Lower Pliocene age. From 

 this center of radiation these primates took their departure, 

 the gorilla and chimpanzee southwestwardly toward the Dark 

 Continent, although a fossil (Pleistocene) chimpanzee jaw 

 associated with a human skull (Homo (Eoanthropus) daw- 

 soni) has recently been found in England, 9 while the gibbons 

 and orang went toward the southeast. The prehuman, on the 

 other hand, remained in central Asia nearest the dispersal 

 center, which, we have seen, is generally true of the latest and 

 most highly specialized of a race. The forms which migrated 

 southward felt the enervating languor of the tropics and re- 

 mained static, if they did not actually retrogress, whereas the 

 prehuman in the more invigorating and variable climate pro- 

 gressed in his evolution toward a higher type. Central Asia 

 has proved to be the theater wherein the highest mammalian 

 evolution could be attained, for here the forms which man 

 has chosen for his companions, the domestic animals, almost 

 without exception attained their evolutionary completion. 



The actual descent from the trees seems to have been due 

 to a chain of events which in many ways parallel those which 

 impelled the emergence. 10 The Miocene uplift, with the con- 



9 Miller, G. S., Jr., "The Jaw of the Piltdown Man." Smithson. Misc. Coll., 

 vol. 65, No. 12, 1915, pp. 1-31. 



10 BarrelI, J., "Probable Relations of Climatic Change to the Origin of the 

 Tertiary Ape-man." Scientific Monthly, January, 1917, pp. 16-26. 



