16 THE EVOHTTIOX THEORY 



seemi'tl to slunv that cn en the higlu'st and most comprehensive groups 

 :nv sharply ilcHncil oti" Troiu one another. 



Let luc adil that this doctrine of the absolute nature of species 

 was not fully elahoratod till our own day, when the Swiss (afterwards 

 American ) natm-alist. Louis Agassiz, went so far as to maintain that not 

 only the hiijhest and the lowest categories, but all those coming between 

 them, were categories established and sharply separated by Nature 

 hei-self. But in spite of nuich ingenuity and his wide and compre- 

 liensive outlook he exerted himself in vain to find satisfactory and 

 realh' characteristic definitions of wdiat was to be considered a class, 

 an order, a family, or a genus. He did not succeed in finding a 

 rational definition of these systematic concepts, and his endeavour 

 may be regarded as the last important attempt to proj) up an 

 interpretation of nature already doomed to fall. But in referring to 

 Louis Agassiz I have anticipated the historical course of scientific 

 development, and must therefore go back to the last quarter of the 

 eighteenth century. 



The first unmistakable pioneer of the theory of descent, which 



now emerged for the first time as a scientific doctrine, was our great 



poet Goethe. He has indeed been often named as the founder of the 



theory, but that seems to me saying too much. It is true, however, 



that the inquiring mind of the poet certainly recognized in the 



structure of 'related' animals the marvellous general resemblances 



amid all the difterences in detail, and he probed for the reason of 



these form-relations. Through the science of ' comparative anatomy,' 



as it was taught at the close of the century by Kielmeyer, Cuvier's 



teacher, and later by Cuvier himself, Blumenbach, and others, 



numerous facts had become known, which paved the way for such 



questions. It had, for instance, been recognized that the arm of man, 



the wing of the bird, the paddle of the seal, and even the foreleg of 



the horse, contain essentially the same chain of bones, and Goethe had 



already expressed these relations in his well-know^n verse, 



' Alle Gestalten sind ahnlich, cloch keine gleichet der andern, 

 Und so deutet der Chor auf ein geheimes Gesetz.' 



As to what this law was he did not at that time pronounce an opinion, 

 though he may even then have thought of the transformation of species. 

 At first he contented himself with seeking for an ideal archetype or 

 ' L"rtjT)us ' which was supposed to lie at the foundation of a larger or 

 smaller group. He discovered the archetypal plant or ' L'rpflauze,' when 

 he rightly recognized that the parts of the flower are nothing more 

 than modified leaves. He spoke plainly of the 'metamorphosis of 

 plants,' meaning by that the transformation of his ' archetype ' into the 



