DIFFICULTIES ON THEORY 181 



own defence and for the destruction of its prey ; but 

 some authors suppose that at the same time this snake 

 is furnished with a rattle for its own injury, namely, 

 to warn its prey to escape. I would almost as soon 

 believe that the cat curls the end of its tail when 

 preparing to spring, in order to warn the doomed 

 mouse. But I have not space here to enter on this 

 and other such cases. 



Natural selection will never produce in a being 

 anything injurious to itself, for natural selection acts 

 solely by and for the good of each. No organ will be 

 formed, as Paley has remarked, for the purpose of 

 causing pain or for doing an injury to its possessor. 

 If a fair balance be struck between the good and 

 evil caused by each part, each will be found on the 

 whole advantageous. After the lapse of time, under 

 changing conditions of life, if any part comes to be 

 injurious, it will be modified ; or if it be not so, the 

 being will become extinct, as myriads have become 

 extinct. 



Natural selection tends only to make each organic 

 being as perfect as, or slightly more perfect than, the 

 other inhabitants of the same country with which it 

 has to struggle for existence. And we see that this is 

 the degree of perfection attained under nature. The 

 endemic productions of New Zealand, for instance, are 

 perfect one compared with another ; but they are now 

 rapidly yielding before the advancing legions of plants 

 and animals introduced from Europe. Natural selec- 

 tion will not produce absolute perfection, nor do we 

 always meet, as far as we can judge, with this high 

 standard under nature. The correction for the aberra- 

 tion of light is said, on high authority, not to be 

 perfect even in that most perfect organ, the eye. If 

 our reason leads us to admire with enthusiasm a multi- 

 tude of inimitable contrivances in nature, this same 

 reason tells us, though we may easily err on both 

 sides, that some other contrivances are less perfect. 

 Can we consider the sting of the wasp or of the bee 

 as perfect, which, when used against many attacking 



