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. 
