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CHAPTEE IV. 



VARIATION AND NATURAL SELECTION. 



EVERYTHING, so far as in it lies, said Benedict Spinoza, tends 

 to persist in its own being. This is the law of persistence. 

 It forms the basis of Newton's First Law of Motion, which 

 enunciates that, if a body be at rest, it will remain so unless 

 acted on by some external force ; or, if it be in motion, it 

 will continue to move in the same straight line and at a 

 uniform velocity unless it is acted on by some external 

 force. Practically every known body is thus affected by 

 external forces ; but the law of persistence is not thereby 

 disproved. It only states what would happen under certain 

 exceptional or perhaps impossible circumstances. To 

 those ignorant of scientific procedure, it seems unsatis- 

 factory, if not ridiculous, to formulate laws of things, not as 

 they are, but as they might be. Many well-meaning but 

 not very well-informed people thus wholly misunderstand 

 and mistake the value of certain laws of political economy, 

 because in those laws (which are generalized statements of 

 fact under narrowed and rigid conditions, and do not pre- 

 tend to be inculcated as rules of conduct) benevolence, 

 sentiment, even moral and religious duty, are intention- 

 ally excluded. These laws state that men, under motives 

 arising out of the pursuit of wealth, will act in such and 

 such a way, unless benevolence, sentiment, duty, or some 

 other motive, lead them to act otherwise. Such laws, 

 which hold good, not for phenomena in their entirety, but 

 for certain isolated groups of facts under narrowed con- 

 ditions, are called laws of the factors of phenomena. And 

 since the complexity of phenomena is such that it is 



