92 THE PALEONTOLOGIC RECORD 



area for a long period, and we find several greatly differing human 

 physical stocks in different geographic regions, just as we find differing 

 stocks of mammals and birds. 



With the lack of physical diversity among the people of the western 

 hemisphere, there is also noticeable a resemblance of the whole group 

 to the people of the adjacent region of Asia. Judged by the standards 

 of differentiation which we obtain through a study of the history of 

 geographical distribution of other mammalian groups, we have every 

 reason to think that the people of America are immigrants who came 

 from the Asiatic region and spread themselves over America after the 

 period of the first great physical differentiation of the race, and so 

 recently that a second stage of physical differentiation has not yet had 

 time to develop. On the other hand, the time measured in years has 

 been long enough so that linguistic differentiation could take place. 



Inasmuch as a large part of human history falls within the Quater- 

 nary period, the question naturally arises as to whether the principal 

 migrations of man to the American continent occurred before, during 

 or after the Glacial epoch. 



As primates are naturally animals of a warm or temperate zone, 

 it is hardly to be presumed that primitive man came to America during 

 the ice age, though there is a possibility of immigration in some of the 

 interglacial epochs. Judging from what is suggested through study of 

 physical differentiation, it appears improbable that man came over as 

 early as the epoch preceding the ice age. In other groups of animals 

 spread over large areas, marked physical differentiation has ordinarily 

 taken place in a space of time comparable to the Glacial epoch. Had 

 man been present in America during this long period, widely differing 

 physical types would almost certainly have developed. On the whole it 

 seems most probable that he arrived after the end of the last division 

 of glacial time, or very near the beginning of the present epoch. 

 Whether his arrival is shown to have occurred just before or just after 

 the beginning of this epoch remains to be determined. 



In conclusion it seems desirable to call the attention of paleontolo- 

 gists once more to the important part which their work must play in 

 obtaining the information which we need with reference to the history 

 of man and his antecedents. Only a small beginning has been made, 

 and the results which must come are of great importance in the large 

 problem of man's relation to nature. It is necessary that paleontolo- 

 gists keep the subject before them, in order to make certain that all 

 information bearing upon it may be recognized as it becomes available, 

 and be given its proper place in relation to other evidence now at hand. 



