CHIFF-CHAFF 
Although a critical investigation of the complex and diver- 
gent activities of the lower animals lends so little support 
to this theory, it reveals abundant evidence of a law of 
uniformity extending to all the varied incidents of the lives 
of the different individuals of the same species, the magnitude 
and importance of which, so I am inclined to believe, has 
been obscured by an incessant quest for variation. It is 
only when we carefully consider the conditions of existence 
of most species, and understand how favourable those condi- 
tions are to any innate modifiability, that we can appre- 
ciate the full significance of this law. So favourable, 
indeed, are they that it has often seemed to me a 
remarkable fact, and one very difficult of explanation, that 
individuality is not of frequent and persistent occurrence. 
Let us take the case of the Chiff-chaff. After reading of the 
way in which it examines and joins in the various disturb- 
ances around, the manner in which the breeding area is fixed 
and adhered to, the choice of a certain tree as headquarters, 
and the systematic working towards the boundaries, culmin- 
ating in a combat or game with its neighbours, no one, 
I imagine, will deny the variety of its activities nor the 
complicated movements involved in such activities; but, in 
addition, this bird possesses vigour in excess of its immediate 
needs in a greater degree than many other species, resulting 
in a pronounced restless energy and ceaseless activity. In 
such an existence as this we must believe that opportunities 
for modification will constantly arise, yet apparently no 
individual attempt is made to depart from the rules of the 
species, for we find that, in so far as the systematic study 
of different members of the same species enables us to judge, 
all these activities, both simple and complex, are similarly 
performed under the same appropriate circumstances by all 
the individuals of the same species. 
And pursuing the subject somewhat further, if we not 
only accept variation as an established fact, but look upon 
intelligence as the principal factor, as it is so regarded by 
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