eries of
remains showing continual advancement over a period of nearly 500,000
years--the Pithecanthropus, Heidelberg, Piltdown, and Neanderthal,
though expressing gradations of development in the order named, appear
to be unrelated in their origin and descent, and are classed as
separate species long since extinct. The Cro-Magnon people seem more
directly related to modern man. Perhaps in the Neolithic Age they may
have been the forebears of present races, either through direct or
indirect lines.

_The Unity of the Human Race_.--Though there are evidences, as shown
above, that there were many branches of the human race, or species,
some of which became extinct without leaving any records of the passing
on of their cultures to others, there is a pretty generally concerted
opinion that all branches of the human race are related and have sprung
from the same ancestors. There have been differences of opinion
regarding this view, some holding that there are several centres of
development in which the precursor of man assumed a human form
(polygenesis), and others holding that according to the law of
differentiation and zoological development there must have been at some
time one origin of the species (monogenesis). So far as the scientific
investigation of mankind is concerned, it is rather immaterial which
theory is accepted. We know that multitudes of tribes and races differ
in minor parts of structure, differ in mental capacity, and hence in
qualities of civilization, and yet in general form, brain structure,
and mental processes, it is the same human being wherever found. So we
may assume that there is a unity of the race.

If we consider the human race to have sprung from a single {67} pair,
or even the development of man from a single species, it must have
taken a long time to have developed the great marks of racial
differences that now exist. The question of unity or plurality of race
origins has been much discussed, and is still somewhat in controversy,
although the predominance of evidence is much in favor of the descent
of man from a single species and from a single place. The elder
Agassiz held that there were several separate species of the race,
which accounts for the wide divergence of characteristics and
conditions. But it is generally admitted from a zoological standpoint
that man originated from a single species, although it does not
necessarily follow that he came from a single pair. It is the