Chap. VII. 
THE EACES OF MAN. 
249 
special service to him. The intellectual and moral or 
social faculties must of course be excepted from this re- 
mark ; but differences in these faculties can have had 
little or no influence on external characters. The vari- 
ability of all the characteristic differences between the 
races, before referred to, likewise indicates that these 
differences cannot be of much importance ; for, had 
they been important, they would long ago have been 
either fixed and preserved, or eliminated. In this 
respect man resembles those forms, called by naturalists 
protean or polymorphic, which have remained extremely 
variable, owing, as it seems, to their variations being of 
an indifferent nature, and consequently to their having 
escaped the action of natural selection. 
We have thus far been baffled in all our attempts 
to account for the differences between the races of man ; 
but there remains one important agency, namely Sexual 
Selection, which appears to have acted as powerfully 
on man, as on many other animals. I do not intend 
to assert that sexual selection will account for all the 
differences between the races. An unexplained resi- 
duum is left, about which we can in our ignorance 
only say, that as individuals are continually born with, 
for instance, heads a little rounder or narrower, and 
with noses a little longer or shorter, such slight dif- 
ferences might become fixed and uniform, if the un- 
known agencies which induced them were to act in a 
more constant manner, aided by long-continued inter- 
crossing. Such modifications come under the provi- 
sional class, alluded to in our fourth chapter, which for 
the want of a better term have been called spontaneous 
variations. Nor do I pretend that the effects of sexual 
selection can be indicated with scientific precision ; but 
it can be shewn that it would be an inexplicable fact if 
man had not been modified by this agency, which has 
