BfiAtOT, ttOW ACQUlMD. 181 



eertain colors, forms, and sounds — was first developed in the 

 mind of man and of the lower animals, is a very obscure sub- 

 ject. The same sort of difficulty is presented if we inquire 

 how it is that certain flavors and odors give pleasure, and 

 others displeasure. Habit in all these cases appears to have 

 come to a certain extent into play ; but there must be some 

 fundamental cause in the constitution of the nervous system 

 in each species. 



Natural selection cannot possibly produce any modification 

 in a species exclusively for the good of another species, 

 though throughout nature one species incessantly takes 

 advantage of and profits by the structures of others. But 

 natural selection can and does often produce structures for 

 the direct injury of other animals, as we see in the fang of 

 the adder, and in the ovipositor of the ichneumon, by which 

 its eggs are deposited 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 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 fur- 

 nished 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 attack 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 chickens. 

 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 pos- 

 sessor. If a fair balance be struck between the good aftid 



