viii Preface 



when I should only have been justified in stating the different 

 aspects of the question. But this will do little harm provided 

 the issue has been sharply drawn. Indeed, it seems to me 

 that the only scientific value, that a discussion of what the 

 French call "les grands problemes de la Biologie" has, is to 

 get a clearer understanding of the relation of what is known 

 to what is unknown or only surmised. 



In some quarters speculation concerning the origin of the 

 adaptation of living things is frowned upon, but I have failed 

 to observe that the critics themselves refrain entirely from 

 theorizing. They shut one door only to open another, which 

 also leads out into the dark. To deny the right to speculative 

 thought would be to deny the right to use one of the best 

 tools of research. 



Yet it must be admitted that all speculation is not equally 

 valuable. The advance of science in the last hundred years 

 has shown that the kind of speculation that has real worth is 

 that which leads the way to further research and possible 

 discovery. Speculation that leads to this end must be recog- 

 nized as legitimate. It becomes useless when it deals with 

 problems that cannot be put to the actual test of observation 

 or experiment. It is in this spirit that I have approached the 

 topics discussed in the following pages. 



The unsophisticated man believes that all other animals 

 exist to minister to his welfare ; and from this point of view 

 their adaptations are thought of solely in their relation to 

 himself. A step in advance was taken when the idea was 

 conceived that adaptations are for the good of the organisms 

 themselves. It seemed a further advance when the con- 

 clusion was reached that the origin of adaptations could be 

 accounted for, as the result of the benefit that they conferred 

 on their possessor. This view was the outcome of the accep- 

 tation of the theory of evolution, combined with Darwin's 

 theory of natural selection. It is the view held by most 

 biologists at the present time; but I venture to prophesy 



