76 
DARWINISM 
CHAP. 
two years the sparrows began to attack them, and thereafter 
destroyed them quite as readily as the yellow ones; and he 
believes it was merely because some bolder sparrow than the 
rest set the example. On this subject Mr. Charles C. Abbott 
well remarks : “ In studying the habits of our American birds 
—and I suppose it is true of birds everywhere—it must at all 
times be remembered that there is less stability in the habits 
of birds than is usually supposed ; and no account of the habits 
of any one species will exactly detail the various features of 
its habits as they really are, in every portion of the terri¬ 
tory it inhabits.” 1 
Mr. Charles Dixon has recorded a remarkable change in the 
mode of nest-building of some common chaffinches which were 
taken to New Zealand and turned out there. He says: “The 
cup of the nest is small, loosely put together, apparently lined 
with feathers, and the walls of the structure are prolonged for 
about 18 inches, and hang loosely down the side of the 
supporting branch. The whole structure bears some re¬ 
semblance to the nests of the hangnests (Icteridse), with the 
exception that the cavity is at the top. Clearly these New 
Zealand chaffinches were at a loss for a design when fabricat¬ 
ing their nest. They had no standard to work by, no nests of 
their own kind to copy, no older birds to give them any instruc¬ 
tion, and the result is the abnormal structure I have just 
described.” 2 
These few examples are sufficient to show that both the 
habits and instincts of animals are subject to variation; and 
had we a sufficient number of detailed observations we should 
probably find that these variations were as numerous, as 
diverse in character, as large in amount, and as independent 
of each other as those which we have seen to characterise 
their bodily structure. 
The Variability of Plants. 
The variability of plants is notorious, being proved not only 
by the endless variations which occur whenever a species is 
largely grown by horticulturists, but also by the great difficulty 
that is felt by botanists in determining the limits of species in 
1 Nature, vol. xvi. p. 163 ; and vol. xi. p. 227. 
2 Ibid., vol. xxxi. (1885), p. 533. 
