190 UTILITARIAN DOCTRINE HOW FAR TRUE: Chap. VI. 



some maimnals, and a host of majTnificently-colored butterflies 

 and some other insects, have been rendered beautiful for 

 beauty's sake ; but this has Ijcen cfTected not for the dehf^ht 

 of man, but throup^'h sexual selection, that is, from the more 

 beautiful males liaving been continually preferred by their less 

 ornamented females. So it is Avith the music of birds. We 

 may infer from all this that a similar taste for lieautiful colors 

 ami for musical sounds runs throug-h a large part of the animal 

 kingilom. AVhen tlie female is as beautifully colored as the 

 male, Avhich is not rarely the case with birds and butterflies, 

 the cause simply lies in the colors acquired throuo-h sexual se- 

 lection having been transmitted to both sexes, instead of to 

 the males alone. In some instances, however, the acquirement 

 of conspicuous colors by the female may have been checked 

 through natural selection, on account of the danger to which 

 she would thus have been exposed during incubation. 



Natural selection cannot possibly produce any modification 

 in any one species exclusively for the good of another species ; 

 though throughout Nature one species incessantly takes advan- 

 tage of, and profits by, the structure of others. But natural 

 selection can and does often produce structures for the direct 

 injury of otlicr animals, as we see in the fang of the adder, and 

 in the ovipositor of the ichneumon, by which its eggs are depos- 

 ited in the living bodies of other insects. If it could be proved 

 that any part of the structure of any one species had been 

 formed for the exclusive good of another species, it would 

 annihilate my theory, for such could not have been produced 

 through natural selection. Although many statements may 

 be found in Avorks on natural history to tliis eflcct, 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 supjiose 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 

 wlicn ])reparing 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 any thing 

 injurious to itself, for natural selection acts solely by and for 

 the good of each. No organ will be formed, as Palcy has 

 remarked, for the purpose of causing pain or fordoing an injury 

 to its possessor. If a fivir balance be struck between the good 

 a-.id evil caused by each part, each will 1w found on the whole 



