p. 234. t p. 207. 
280 
corporeal structures.”* How important Mr. Darwin 
esteems this principle to be may be seen from the follow 
ing statement : “ If it could be demonstrated that any 
complex organism existed which could not possibly 
have been formed by numerous successive slight modi 
fications, my theory would absolutely break down.” 
The process will be a more or less protracted one—“No 
complex instinct can possibly be produced through Natural 
Selection except by the slow and gradual accumulation 
of numerous slight yet profitable variations.”']’ 
Now in considering this theory, the first thing to be 
borne in mind is that in those cases in which we have an 
instinct correlated to a particular structure and to certain 
outward conditions, no change can be profitable and, 
therefore, if any change takes place it will take place 
apart from Natural Selection. But this is not all. For 
if it be true that Natural Selection is actively engaged 
in preserving the stability of species in connection with 
unchanged conditions, then it is surely equally reasonable 
to suppose that it would tend to promote the constancy 
of instinct where change was useless at the least, and 
might so easily prove prejudicial. If Natural Selection 
is to be invoked to alter old established instincts, it must 
be in the face of changed conditions and new problems. 
Mr. Darwin insists that the variations of instinct shall 
be slight, that they shall be the result of variations of 
instinct due to sexual reproduction, and that favourable 
variations shall be selected. 
Now if circumstances altered very gradually we could 
then believe that the slow process of the Natural Selection 
of slight favourable variations might suffice to secure the 
well-being of the race. But very often new circumstances