158 NATURAL SELECTION VII 
curious modifications of plumage, and the capacity of per- 
petual egg-laying. In pigeons we have a still more remark- 
able proof of the universality of variation, for it has been at 
one time or another the fancy of breeders to change the form 
of every part of these birds, and they have never found the 
required variations absent. The form, size, and shape of bill 
and feet have been changed to such a degree as is found only 
in distinct genera of wild birds; the number of tail feathers 
has been increased, a character which is generally one of the 
most permanent nature, and is of high importance in the 
classification of birds ; and the size, the colour, and the habits 
have been also changed to a marvellous extent. In dogs, 
the degree of modification and the facility with which it is 
effected is almost equally apparent. Look at the constant 
amount of variation in opposite directions that must have 
been going on to develop the poodle and the greyhound from 
the same original stock! Instincts, habits, intelligence, size, 
speed, form, and colour have always varied, so as to produce 
the very races which the wants or fancies or passions of 
men may have led them to desire. Whether they wanted a 
bull-dog to torture another animal, a greyhound to catch a 
hare, or a bloodhound to hunt down their oppressed fellow- 
creatures, the required variations have always appeared. 
Now this great mass of facts, of which a mere sketch has 
been here given, are fully accounted for by the “Law of 
Variation ” as laid down at the commencement of this paper. 
Universal variability—small in amount, but in every direction, 
ever fluctuating about a mean condition until made to advance 
in a given direction by “selection,” natural or artificial—is 
the simple basis for the indefinite modification of the forms 
of life ; partial, unbalanced, and consequently unstable modi- 
fications being produced by man, while those developed under 
the unrestrained action of natural laws are at every step self- 
adjusted to external conditions by the dying out of all 
unadjusted forms, and are therefore stable and comparatively 
permanent.1 To be consistent in their views, our opponents 
must maintain that every one of the variations that have 
rendered possible the changes produced by man have been 
1 That the variations occurring among wild animals are ample both in num- 
ber and amount is proved in Darwinism, chap. iii. 
