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 
Lamarckism alone can explain the causes 
of evolution. But Darwinism can ex- 
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 
solution. “We must not conceal from 
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 causal science, can never reach 
completeness, since every new cause ascertained only 
gives rise to fresh questions concerning the cause of 
this cause.” 
Return to the 
position of 
Darwin, 
The final word 
still far distant. 
