X PREFACE 



concerning Nature — or at any rate, infinitely less than 

 does any peasant or gardener who is in daily intercourse 

 with her. 



Peasants and gardeners, however, are not students of 

 Nature, unless they happen to have acquired the art of 

 interrogation. 



This art forms the gateway to all knowledge in natural 

 science. In biology it is associated with quite especial 

 difficulties, and so it should occupy the central position 

 in the whole doctrine. 



In the present book I have endeavoured to frame the 

 theoretical considerations concerning biology, in such 

 a way that there can no longer be any doubt that, in 

 their very nature, biological doctrines always remain 

 unsolved problems. 



In Nature everything is certain; in science everything 

 is problematical. Science can fulfil its purpose only 

 if it be built up like a scaffolding against the wall 

 of a house. Its purpose is to ensure the workman a 

 firm support everywhere, so that he may get to any 

 point without losing a general survey of the whole. 

 Accordingly, it is of the first importance that the 

 structure of the scaffolding be built in such a way as to 

 afford this comprehensive view ; and it must never be 

 forgotten that the scaffolding does not itself pertain to 

 Nature, but is always something extraneous. 



From time to time it will always be necessary to 

 renew the scaffolding. And in the present book an 

 attempt of the kind is made. 



The reason for this attempt is that hitherto all the 

 problems dealing with conformity with plan in living 

 Nature have been used simply for the denial of any 

 such conformity. Along such lines it is impossible to 

 make any advance. It used to be assumed that the great 

 majority of animals arose by spontaneous generation 



