THE FACTORS OF ORGANIC EVOLUTION. 117 



On the whole, then, I believe the facts which are at 



present at our disposal justify a return to the position 



of Darwin. Neither Weismannism nor 



Return to the Lamarckism alone can explain the causes 



of evolution. But Darwinism can ex- 

 Darwin. 



plain those causes. Darwin endeavoured 



to show that variations, perhaps even adaptations, were 

 the result of extrinsic factors acting upon the organism, 

 and that these variations or adaptations were increased 

 and improved by natural selection. This is, I believe, 

 the only ground which is at present tenable, and it is 

 but another testimony to the greatness of that man of 

 men that, after exploring for a score of years all the 

 ins and outs of pure selection and pure adaptation, men 

 are now coming back to the position outlined and un- 

 swervingly maintained by him. 



Finally, we ought not to suppose that we have al- 

 ready reached a satisfactory solution of the evolution 



problem, or are, indeed, near such a 

 The final word solutioru We must not conceal from 

 still far distant. , .. ,, ... 



ourselves the fact, says Roux, " that 



the causal investigation of organism is one of the most 

 difficult, if not the most difficult, problem which the 

 human intellect has attempted to solve, and that this 

 investigation, like every causaFscience, can never reach 

 completeness, since every new cause ascertained only 

 gives rise to fresh questions concerning the cause of 

 this cause." 



