204 LECTURES ON BIOLOGY 



if artificial selection could not point to any successes, i.e., if their 

 supporters could employ here, too, their only strategic method of 

 defending themselves behind the fortifications of the impossibility 

 of controlling their hypotheses. But in no case can the facts 

 of artificial selection be employed for proving empirically the 

 doctrine of natural selection, for all that they can do is to render 

 possible the idea of natural selection and its explanation.' 



' Never was there a theory so completely without proofs taken 

 from experience. All hypotheses of the doctrine are put for- 

 ward as self-evident, and are thus so much without an empirical 

 foundation that even the first hypothesis of the theory, the 

 survival of the fittest in the struggle for existence, is an assump- 

 tion which is supported by no observation and the justification of 

 which is confuted by everything that experience may ascertain.' 



These are grave accusations made by a serious thinker who 

 certainly cannot be suspected of dogmatic prejudice. Let us now 

 consider what are the grounds upon which Wolff takes up his 

 hostile attitude. 



If we recall the many results of artificial selection, if we think 

 of the various races of pigeon, or of the pheasant in which 

 Japanese breeders have produced tail-feathers 4 metres long, it 

 would seem as if a natural limit did not exist ; as if, in fact, the 

 organism were ' like clay in the hands of the potter,' to which 

 selection can impart any desired form. But if we examine with- 

 out prejudice the various factors we shall observe everywhere 

 lines of demarcation beyond which selection is not able to pass. 



When, in 1850, the systematic cultivation of the sugar-beet 

 was taken up in this country, the sugar in the beet-root 

 (Beta vulgaris) from which the sugar-beet had been produced by 

 artificial selection was at that time not more than 7 to 8 per 

 cent. To-day it is 14 to 16 per cent. Beyond this it has been 

 found impossible to increase the percentage of sugar, even in 

 spite of determined efforts and the most careful selection. 



The weight of a gooseberry was towards the end of the 

 eighteenth century about 15 grammes. In the course of seventy 

 years this was increased to 60 grammes, but since then the weight 

 has remained at that point, though theoretically there is no 

 reason why gooseberries should not reach the size of apples or 

 pears. A similar limitation is apparent in other cases, but are 



