THE BIRTHPLACE OF MAN 601 
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 defoned. 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 Bulevntile: 
gists keep the subject before them, in order to make certain that all 
information bearing upon it may be recognized as it becomes ay ailable, 
and be given its proper place in relation to other evidence now at hand. 
VoL. LXXviI.—4l 
