170 GENERAL DISCUSSION [ch. xiv 



the reverse. Also evolution could only go on provided that 

 natural selection could act as desired, another assumption. Then 

 the freedom of action of selection was destroyed by Fleeming 

 Jenkin's criticism, though the fact was hardly realised. Finally, 

 selection proved itself incapable of explaining many of the facts 

 of geographical distribution, a subject which is completely 

 bound up with evolution. 



Immense effort was put into the study of adaptation fifty to 

 sixty years ago (p. 52), but with little or no result other than to 

 show that no one in his wildest dreams could attach adaptational 

 value to the bulk of the structural characters that distinguish 

 one plant from another, and show that evolution has really gone 

 on. There was also no doubt that what little adaptation did show 

 decreased rapidly as one went up the scale above the rank of 

 genus ; but the higher divisions were supposed to be made by the 

 killing out of transitions, which would imply that selection came 

 more and more into play to make larger and larger divisions. The 

 facts, when judged in the light of the theory of natural selection, 

 are evidently somewhat incompatible. 



Early in this century de Vries brought in the theory of muta- 

 tion or sudden change, which in many respects got over the worst 

 difficulties of Darwinism, and would have surmounted more had 

 not people taken up a somewhat illogical attitude with regard to it. 

 It was admitted that small mutations could take place, but people 

 were averse to admitting large ones, for that would probably 

 remove any effect of natural selection in guiding evolution. It 

 would be almost absurd to suppose that it showed its work by the 

 production of large and sudden differences, though it is not im- 

 possible, for one may imagine it perhaps selecting slight genie 

 changes, and these being added up till the strain in the nucleus 

 produced some kind of kaleidoscopic effect by a readjustment. 

 The writer suggested in 1907 that "a group of allied species 

 represents so many more or less stable positions of equilibrium in 

 cell division" (70). But though by the adoption of small muta- 

 tions the power as a determinant of evolution was taken away 

 from natural selection, so that it could no longer start the im- 

 proved adaptations, it was expected to carry them on and to 

 increase them, gradually or by further mutation. Of course it 

 would only carry on those which had, so to speak, passed through 

 its sieve, and had proved to be of definite value. We were still, 

 however, without any indication that the characters produced in 

 the small mutation had any adaptational value, so that their 

 survival would usually be due simply to the fact that natural 



