CH. XIV] GENERAL DISCUSSION 165 



mechanism by which these changes were to be effected, i.e. to the 

 struggle for existence that was a famiUar everyday experience, 

 allowing those gifted by nature or by parents, or by chance, to 

 succeed, while the non-gifted usually failed. As every living 

 being tends to produce more offspring than there is room for, 

 some must obviously be picked out, and this selection, or 

 "survival of the fittest", Darwin called natural selection. Being 

 so familiar, it had a great psychological appeal, and was soon 

 taken up in all directions. It was evidently an almost complete 

 reversal of special creation ; instead of being created, beings were 

 evolved, and instead of being discontinuous, the process was 

 continuous. 



Picking out only variations that gave some advantage, natural 

 selection worked by what we may call gradual adaptation 

 (p. 4), which was an essential feature of the theory. But it is 

 clear that a small improvement in adaptation would not be 

 enough to create a new species, which is usually more or less 

 sterile with its near relatives (a functional difference), and shows 

 various structural differences as well. It had to be assumed, 

 therefore, that the process would go on until the line of mutual 

 sterility had been passed, and the differences had become great 

 enough to mark it as a new species. It was the structural dif- 

 ferences that showed that there had been any evolution at all, 

 and so it had to be assumed also that they were adaptational, 

 marking the adaptational advantages that had accrued to the 

 organism. Functional adaptation was ignored, though the mor- 

 phologists had long insisted that structure had little or nothing 

 necessarily to do with function. 



The freedom of the position of natural selection was really lost 

 very early in its history, when Darwin had to give way to the 

 criticism of a well-known professor of engineering, Fleeming 

 Jenkin, who pointed out that unless a great many individuals 

 varied in the same direction over the whole of a considerable 

 area, the improvement would promptly be lost by crossing. 

 Darwin therefore stipulated for such a beginning, which seems 

 only likely to happen under the action of some external force, and 

 which practically excludes the action of biological factors, which 

 are usually local. Improvement seemed unlikely in the fluctuating 

 variation upon which Darwin usually relied, for some might go 

 up when others went down, and crossing would level them. This 

 criticism took much of the spring out of the action of natural 

 selection, for instead of remaining a simple affair of individuals, 



