280 THE ORIGIN OF SPECIES 



part of the structure of any one species had been formed 

 for the exclusive good of another species, it would an- 

 nihilate my theory, for such could not have been pro- 

 duced through natural selection. Although many state- 

 ments may be found in works on natural history to this 

 effect, I cannot find even one which seems to me of any 

 weight. It is admitted that the rattlesnake has a poison- 

 fang for its own defence, and for the destruction of its 

 prey; but some authors suppose that at the same time 

 it IS furnished with a rattle for its own injury, namely, 

 to warn its prey. 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. It is a 

 much more probable view that the rattlesnake uses its 

 rattle, the cobra expands its frill, and the puff-adder 

 swells while hissing so loudly and harshly, in order to 

 alarm the many birds and beasts which are known to at- 

 tack even the most venomous species. Snakes act on the 

 same principle which makes the hen ruffle her feathers 

 and expand her wings when a dog approaches her chick- 

 ens; but I have not space here to enlarge on the many 

 ways by which animals endeavor to frighten away their 

 ^enemies. 



Natural selection will never produce in a being any 

 structure more injurious than beneficial to that being, 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 



