Tropisms and Instincts as Adaptations 413 



accounted for on the ground of their benefit to the indi- 

 vidual or to the race; and it does not seem reasonable to 

 make up one explanation for the origin of those that are 

 essential, and another for those that are of little use or even 

 of no use at all. 



From what has been already said more than once, while 

 discussing each particular case, the simplest course appears 

 to be in all instances to look upon these instincts as having 

 appeared independently of the use to which they may be 

 put, and not as having been built up by selection of the 

 individual variations that happen to give an organism some 

 advantage over its fellows in a life and death struggle. It 

 appears reasonable to deal with the origin of tropisms and 

 instincts in general in the same way as in dealing with 

 structures ; for, after all, the tropism is only the outcome 

 of some material or structural basis in the organism. 



No attempt has been made here to interpret the more com- 

 plex reactions of the nervous system, for until we can get 

 some insight into the meaning of the simpler processes, we 

 are on safer ground in dealing with these first. 



