22 I 
of all phenomena, and capable of serving as a very touchstone 
whereby the value of competing theories of the universe may be 
effectually tested. His prescience has been justified by our expe 
rience. The greatest scientific event of the present time is the wide 
acceptance of the theory of evolution and its use as a weapon of 
offence and defence. . . . Now it would be difficult to find a 
more searching test of that theory’s truth than is supplied by a 
careful study of instinct.”—(St. George Mivart. The Fortnightly 
Review, vol. xxxvii., p. 321.) 
Mr. Romanes says :— 
“Perhaps in no one department of his work has Mr. Darwin been 
more successful in displaying the probable causation of biological 
facts than he has been in the province of instinct. If we accept the 
theory of Natural Selection as of any validity at all in explaining 
the evolution of structures, it must also be of some validity in ex 
plaining the evolution of instincts. ... If the theory of evolution 
is of any validity in any case as a scientific interpretation of natural 
phenomena, nowhere is it more successful in this respect than in 
the domain of instinct.”—(The Fortnightly Review, vol. xxxviii., 
p. 94.) 
It may be remarked in passing that Mr. Darwin does 
not seem to anticipate that the study of the phenomena of 
instinct will prove especially favourable to the theory of 
Natural Selection. 
“ Many instincts are so wonderful that their development will 
probably appear to the reader a difficulty sufficient to overcome my 
whole theory.”—(Origin of Species, p. 203.) 
“ I do not pretend that the facts given in this chapter strengthen 
in any great degree my theory, but none of them annihilate it.”— 
(Ibid. p. 233.) 
This modified statement may be due to the modesty of 
genius, but it is in remarkable contrast to the opinion 
expressed by Mr. Romanes. 
In order to understand the part which Natural Selection 
is supposed to play in connection with instinct, it will be 
necessary to understand clearly what instinct is. In order 
to do this we will begin by availing ourselves of the Duke