314 DARWINIANISM. 



It is in such an example as this of the porcupine that 

 we see the veritable purpose of the book itself. The 

 rattle of the porcupine's tail is an expression ; and 

 therein lies a proof of natural selection. Such an 

 expression is an advantage to the animal ; and this 

 advantage, a result of mere accidental or natural variation 

 in the first place, was gradually improved by a process 

 of selection, equally accidental, equally natural, in the 

 second place, through ancestor after ancestor, during the 

 infinitude of time, into the full-formed implement we 

 see. The first individual that discovered the advantage 

 of a sound in its tail its spines otherwise, being 

 necessarily already, so far, to the fore (but how we know- 

 not) would make a custom of it, and this custom pass- 

 ing over into the race can, in propriety, be only named 

 inherited habit. This, then, is the theme of the book. 

 The prevalence of inherited habit shall be illustrated 

 into a demonstration of the truth of natural selection. 



