xii PREFACE 



one now claims for Darwin's law of natural selection a rank 

 equal to that of Newton's law of gravitation. 



If we admit the possibility that Kant was right, and that 

 we can never become sufhciently acquainted with organized 

 creatures and their hidden potentialities by aid of purely 

 natural principles, we may be compelled to regard the origin 

 and evolution of life as an ultimate law like the law of gravita- 

 tion, which may be mathematically and physically defined, 

 but cannot be resolved into any causes. We are not willing, 

 however, to make such an admission at the present time and 

 to abandon the search for causes. 



The question then arises, why has our long and arduous 

 search after the causes of evolution so far been unsuccessful? 

 One reason why our search may have failed appears to be that 

 the chief explorers have been trained in one school of thought, 

 namely, the school of the naturalist. They all began their studies 

 with observations on the external form and color of animals 

 and plants; they have all observed the end results of long 

 processes of evolution. Buffon derived his ideas of the causes 

 of evolution from the comparison of the wild and domestic 

 animals of the Old and New Worlds; Goethe observed the com- 

 parative anatomy of man and of the higher animals; Lamarck 

 observed the higher phases of the vertebrate and invertebrate 

 animals; Darwin observed the form of most of the domestic 

 animals and cultivated plants and, finally, of man, and noted 

 the adaptive significance of the colors of flowers and birds, 

 and the relations of flowers with birds and insects; de Vries 

 compared the wild and cultivated species of plants. Thus all 

 the great naturalists in turn — Buffon, Goethe, Lamarck, Dar- 

 win, and de Vries — have attempted to reason backward, as it 

 were, from the highly organized appearances of form and color 

 to their causes. The same is true of the palaeontologists: 



