The Theory of Natural Selection. 259 



before the publication of Darwin's work ; and so much, 

 likewise, for the only reasonable suggestions as to 

 the causes of evolution which up to that time had 

 been put forward, even by those few individuals who 

 entertained any belief in evolution as a fact. It 

 was the theory of natural selection that changed all 

 this, and created a revolution in the thought of our 

 time, the magnitude of which in many of its far-reaching 

 consequences we are not even yet in a position to 

 appreciate ; but the action of which has already 

 wrought a transformation in general philosophy, as 

 well as in the more special science of biology, that 

 is without a parallel in the history of mankind. 



Although every one is now more or less well 

 acquainted with the theory of natural selection, it is 

 necessary, for the sake of completeness, that I should 

 state the theory ; and I will do so in full detail. 



It is a matter of observable fact that all plants and 

 animals are perpetually engaged in what Darwin calls 

 a " struggle for existence." That is to say, in every 

 generation of every species a great many more in- 

 dividuals are born than can possibly survive ; so that 

 there is in consequence a perpetual battle for life going 

 on among all the constituent individuals of any given 

 generation. Now, in this struggle for existence, which 

 individuals will be victorious and live? Assuredly 

 those which are best fitted to live, in whatever respect, 

 or respects, their superiority of fitness may consist. 

 Hence it follows that Nature, so to speak, selects the 

 best individuals out of each generation to live. And not 

 only so ; but as these favoured individuals transmit 

 ' their favourable qualities to their offspring, according to 

 S 2 



