evolution after the various races had left the
aboriginal home in which the physical characteristics became fixed.
Thus the races, though alike in their physical response to climate,
may possibly be different in their mental response because they have
approached America by different paths.

Before we can understand how man may have been modified on his way from
his original home to America, we must inquire as to the geographical
situation of that home. Judging by the climate which mankind now finds
most favorable, the human race must have originated in the temperate
regions of Europe, Asia, or North America. We are not entirely without
evidence to guide to a choice of one of the three continents. There is
a scarcity of indications of preglacial man in the New World and an
abundance of such indications in the Old. To be sure, several skulls
found in America have been supposed to belong to a time before the last
glacial epoch. In every case, however, there has been something to throw
doubt on the conclusion. For instance, some human bones found at Vero
in Florida in 1915 seem to be very old. Certain circumstances, however,
suggest that possibly they may not really belong to the layers of gravel
in which they were discovered but may have been inserted at some later
time. In the Old World, on the contrary, no one doubts that many human
skulls and other parts of skeletons belong to the interglacial epoch
preceding the last glacial epoch, while some appear to date from still
more remote periods. Therefore no matter at what date man may have
come to America, it seems clear that he existed in the Old World much
earlier. This leaves us to choose between Europe and Asia. The evidence
points to central Asia as man's original home, for the general movement
of human migrations has been outward from that region and not inward.
So, too, with the great families of mammals, as we know from fossil
remains. From the earliest geological times the vast interior of Asia
has been the great mother of the world, the source from which the most
important families of living things have come.

Suppose, then, that we place in central Asia the primitive home of
the thin-skinned, hairless human race with its adaptation to a highly
variable climate with temperatures ranging from freezing to eighty
degrees. Man could not stay there forever. He was bound to spread to
new regions, partly because of his innate migratory tendency and partly
because of Natu