1909.] COXKLIX— THE WORLD'S DEBT TO DARWIN. xlv 



" natural elimination," but he fondly hoped that in time everyone 

 would come to understand it. Over and over again he recognized 

 that natural selection was a negative, an eliminating factor. He 

 never held that it was anything more than a sieve, as De Vries puts 

 it, to sort out favorable from unfavorble variations. 



The only difference of opinion between Darwinians and anti- 

 Darwinians at present is a purely quantitative one as to the amount 

 of value to be assigned to natural selection. It is perfectly evident 

 that organisms which cannot live must die, and that those which are 

 severely handicapped must, on the whole, perish sooner than those 

 which are not so handicapped. No naturalist will question the fact 

 that many ill-adapted forms are eliminated before they can leave 

 offspring. The real question at issue is whether this elimination is 

 severe enough to weed out all but the most favorable variations, as 

 Darwinians generally assume, or whether it weeds out only the 

 least favorable variations, as anti-Darwinians claim. If variations 

 occur in all directions, as Darwin believed, natural selection must 

 eliminate more than half of these in order to be a truly directive 

 factor in evolution ; and the less severe the elimination is the less 

 directive is this factor. This may be illustrated by a diagram of a 

 radiating figure in which the center of the figure represents the 

 norm of a species from which lines, representing variations, proceed 

 in all directions. If natural selection, or elimination, be represented 

 by portions of a circle inclosing this figure and blocking the radii, 

 then one quarter of the circle will block approximately one quarter 

 of the radii ; a semicircle, one half of the radii ; three quarters of 

 the circle, three quarters of the radii ; and in general the more com- 

 pletely the circle (natural selection) blocks the radii (variations) the 

 more directive it becomes. Many recent studies indicate that the 

 elimination due to natural selection is not so extensive as Darwin 

 and his followers believed, and that therefore it is not so important 

 a factor in directing the course of evolution as they supposed. That 

 Darwin himself was much impressed by some such consideration is 

 shown by the statement made in his later works that he thought the 

 most serious mistake which he had made was in attributing too 

 much influence to natural selection, and too little to the inherited 

 effects of environment and of use and disuse upon organisms. 



