X PREFACE 



scepticism. Thus the long period of observation, experiment, 

 and reasoning which began with the French natural philosopher 

 Buffon, one hundred and fifty years ago, ends in 1916 with the 

 general feeling that our search for causes, far from being near 

 completion, has only just begun. 



Our present state of opinion is this: we know to some 

 extent how plants and animals and man evolve; we do not 

 know why they evolve. We know, for example, that there 

 has existed a more or less complete chain of beings from monad 

 to man, that the one-toed horse had a four-toed ancestor, that 

 man has descended from an unknown ape-like form somewhere 

 in the Tertiary. We know not only those larger chains of 

 descent, but many of the minute details of these transforma- 

 tions. We do not know their internal causes, for none of the 

 explanations which have in turn been olTered during the last 

 hundred years satisfies the demands of observation, of experi- 

 ment, of reason. It is best frankly to acknowledge that the 

 chief causes of the orderly evolution of the germ are still en- 

 tirely unknown, and that our search must take an entirely 

 fresh start. 



As regards the continuous adaptability and fitness of liv- 

 ing things, we have a reasonable interpretation of the causes 

 of some of the phenomena of adaptation, but they are the 

 smaller part of the whole. Especially mysterious are the chief 

 phenomena of adaptation in the germ; the marvellous and 

 continuous fitness and beauty of form and function remain 

 largely unaccounted for. We have no scientific explana- 

 tion for those processes of development from within, which 

 Bergson^ has termed "revolution creatrice," and for which 

 Driesch- has abandoned a natural explanation and assumed 



' Bergson, Henri, 1907, U Evolution Creatrice. 



' Driesch, Hans, 1908, The Science and Philosophy of the Organism. 



