Much trustworthy evidence has been collected to show that the whole
world had really been peopled during the period which roughly coincides
with what is known in geology as the Ice Age; that is, when a large part
of the northern and southern hemispheres was subject to invasions of
thick-ribbed ice advancing successively from both poles. The migrations
were most probably begun before the appearance of the first great
ice-wave, then arrested and resumed alternately between the glacial
intervals, and completed after the last glacial epoch, say, some two or
three hundred thousand years ago.
At that time the various wandering groups had already made considerable
progress both in physical and mental respects, as is seen in the
Neanderthal skull, which is the oldest yet found in Europe, standing
about midway between the Javanese ape-man and the present low races. All
were still very much alike, presenting a sort of generalized human type
which may be called Pleistocene man, a common undeveloped form, which
did not begin to specialize--that is, to evolve the existing varieties
until the several primitive groups had reached their respective homes as
disclosed at the dawn of history.