37 Problems of Organic Adaptation 



mechanistic manner. In biology the desire for simple me- 

 chanical explanations is so great that it often causes us to 

 minify the difficulties and magnify the successes of such ex- 

 planations. We may temporarily close our eyes to these 

 difficulties, but they remain and must be reckoned with. 

 Few persons have the intellectual honesty of Darwin, who 

 wrote down at once the objections to his theory as they 

 occurred to him, lest he might forget them, and who con- 

 fessed that he never thought of explaining the evolution 

 of the eye without a shudder. But even if an ultimate 

 mechanistic explanation of adaptations is not possible, it 

 does not follow that we must at once resort to an explana- 

 tion which is either non-mechanistic or supernatural. Many 

 things which were once supposed to be due to supernatural 

 causes are now readily explained by natural ones. The ear- 

 lier students of evolution proposed absurdly simple mechani- 

 cal explanations of the process. Later these were replaced 

 by more complex mechanisms, and when these latter fail to 

 offer a satisfactory explanation the scientific solution must 

 be sought in more and more complex mechanisms; for 

 science deals only with mechanisms, and a scientific explana- 

 tion must be mechanistic. 



Some of the world's great philosophers and scientists, from Aris- 

 totle and Plato to Kant, Schopenhauer, Lamarck, Cope, Bergson, 

 Driesch, and Henderson, have maintained that the fitness and order 

 of nature can be explained only by assuming that there is some sort 

 of teleological principle in nature, which lies back of or runs parallel 

 with the principle of causality something which acts more or less 

 like human will or purpose, and which is itself an uncaused cause 

 lying outside the field of scientific inquiry. 



Kant has expressed this opinion in a well-known passage: "It is 

 quite certain that we cannot become sufficiently acquainted with 

 organized creatures and their hidden potentialities by aid of purely 

 mechanical natural principles, much less that we can explain them; 

 and this is so certain that we may boldly assert that it is absurd for 



