e account for the multitudes of
the types and races of the human being, except by this process of
differentiation which is one of the main factors of evolution.
Accompanying the process of differentiation is that of specialization
and integration. When types become highly specialized they fail to
adapt themselves to new environments, and other types not so highly
specialized prevail. So far as the human race is concerned, it seems
to be evolved according to the law of sympodial development--that is, a
certain specialized part of the human race develops certain traits and
is limited in its adaptability to a specific environment. Closely
allied with this are some individuals or groups possessing human traits
that are less highly specialized, and hence are adaptable to new
conditions. Under new conditions the main stem of development perishes
and the budded branch survives.

We have abundant pictures of this in prehistoric times, and records
show that this also has been the common lot of man. Modern man thus
could not have been developed from any of the living species of the
Anthropoid Apes, but he might have had a common origin in the physical,
chemical, and vital forces that produced the apes. One line of
specialization made the ape, another line made man. Subsequently the
separation of man into the various races and species came about by the
survival of some races for a time, and then to be superseded by a
branch of the same race which differentiated in a period of development
before high specialization had taken place.

_Methods of Recounting Prehistoric Time_.[1]--Present time is measured
in terms of centuries, years, months, weeks, days, hours, minutes, and
seconds, but the second is the determining power of mechanical
measurement, though it is derived mainly by the movement of the earth
around the sun and the turning of the earth on its axis. Mechanically
we have derived the second as the unit. It is easy for us to think in
hours or days or weeks, though it may be the seconds tick off unnoticed
{59} and the years glide by unnoticed; but it is difficult to think in
centuries--more difficult in millions of years. The little time that
man has been on earth compared with the creation of the earth makes it
difficult for us to estimate the time of creation. The much less time
in the historical period makes it seem but a flash in the movement of
the creation.

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