he differences are moderate enough
to be accounted for as due to variation from a single type. Darwin's
summing-up of the evidence as to unity of type throughout the races of
mankind is as distinctly a monogenist argument as those of Blumenbach,
Prichard or Quatrefages--

"Although the existing races of man differ in many respects, as in
colour, hair, shape of skull, proportions of the body, &c., yet, if
their whole organization be taken into consideration, they are found
to resemble each other closely in a multitude of points. Many of these
points are of so unimportant, or of so singular a nature, that it is
extremely improbable that they should have been independently acquired
by aboriginally distinct species or races. The same remark holds good
with equal or greater force with respect to the numerous points of
mental similarity between the most distinct races of man.... Now, when
naturalists observe a close agreement in numerous small details of
habits, tastes and dispositions between two or more domestic races, or
between nearly allied natural forms, they use this fact as an argument
that all are descended from a common progenitor who was thus endowed;
and, consequently, that all should be classed under the same species.
The same argument may be applied with much force to the races of
man."--(Darwin, _Descent of Man_, part i. ch. 7.)

The main difficulty of the monogenist school has ever been to explain
how races which have remained comparatively fixed in type during the
long period of history, such as the white man and the Negro, should, in
even a far longer period, have passed by variation from a common
original. To meet this A.R. Wallace suggests that the remotely ancient
representatives of the human species, being as yet animals too low in
mind to have developed those arts of maintenance and social ordinances
by which man holds his own against influences from climate and
circumstance, were in their then wild state much more plastic than now
to external nature; so that "natural selection" and other causes met
with but feeble resistance in forming the permanent varieties or races
of man, whose complexion and structure still remained fixed in their
descendants (see Wallace, _Contributions to the Theory of Natural
Selection_, p. 319). On the whole, it may be asserted that the doctrine
of the unity of mankind stands on a firmer basis than in previous ages.
It would be premature to jud