lO PREFACE. 



of imagination, and -that the future would find in it 

 some durable points which would outlive the muta- 

 tions of opinion. It is possible that one of these dura- 

 ble gains is my much impugned idea of determinants, 

 and in fact not only will the present essay be made 

 to rest on this idea, but it will also defend it on new 

 grounds, although primarily only as a representation 

 of something which we do not as yet exactly Icnow, but 

 which still exists and on which we can reckon, leavihg 

 it to the future to decide the greater or less resem- 

 blance of our hypothetical construct to nature. 



The real aim of the prese nt essay is to rehabilitate 

 the principle of selection. If I should succeed in rein- 

 stating this principle in its emperilled rights, it would 

 be a source of extreme satisfaction to me; for I am 

 so thoroughly convinced of its indispensability as to 

 believe that its demolition would be synonymous with 

 the renunciation of all inquiry concerning the causal 

 relation of vital phenomena. If we could understand 

 the adaptations of nature, whose number is infinite; 

 only upon the assumption of a teleological principle, 

 then, I think, there would be little inducement to 

 trouble ourselves about the causal connexion of the 

 stages of ontogenesis, for no good reason would 

 exist for excluding teleological principles from this 

 field. Their introduction, however, means the ruin of 

 science. August Weismann. 



Freiburg, Nov. i8, 1895. 



