156 EVOLUTION 



natural selection, or, less metaphorically, the 

 survival of the fittest, the one term referring 

 mainly to the process, the other to the result. 

 The probable course of natural selection may 

 be understood from the case of a country 

 undergoing change of climate. The pro- 

 portional numerical strengths of its species 

 will be changed; some will probably become 

 extinct ; and these changes will seriously 

 affect the others. Immigration of new forms 

 might also occur, with further serious dis- 

 turbance; or, where this is impossible, there 

 will be places in the economy of Nature which 

 might be better filled up. In such cases 

 slight changes in structure or habit which 

 in any way favoured the individuals of any 

 species, by adapting them better to their 

 altered conditions, would tend to be preserved, 

 and natural selection would have free scope 

 for its work of improvement. Moreover, 

 changed conditions increase variability. 



As man produces great results by his 

 artificial selection, what may not natural 

 selection effect ? Man selects only for his 

 own purposes, Nature for the good of the 

 creature itself; man on the more external 

 characters (he has become more adventurous 

 since Darwin's day), Nature on the whole 

 machinery of life; man irregularly and im- 



