THE STUDY OF HEREDITY 335 



frequently shows in his book towards a belief in some kind of 

 supernatural directive power which regulates evolution, and on 

 these lines is a most desirable asset to his arguments ; but it is 

 not the case that the hypothesis has been accepted by the 

 majority of biologists, indeed many repudiate it altogether. 

 Prof. Thomson is certainly more reasonable in one respect than 

 Prof. Bateson, the apostle in this country of the mutation 

 hypothesis. The latter and his school assume that " all 

 organised nature is arranged in disconnected series of groups, 

 differing from each other by differences which are specific." 1 I 

 think that those biologists who have been largely occupied in 

 the study of species and varieties are unanimously of opinion 

 that so-called species very frequently, if not generally, merge 

 into each other by almost insensible gradations. When these 

 links are not found, their absence may reasonably be accounted 

 for by the fact that enormous numbers of forms have dis- 

 appeared in the past, without leaving any traces. Prof. Thomson 

 realises that " species are often connected by intermediate 

 links," but suggests that these links " may have been formed 

 after the species from which they are theoretically supposed to 

 give rise." To me this explanation appears inconceivable. The 

 intermediate links are admittedly there. Therefore the 

 organisms are obviously capable of producing these links be- 

 tween the two extremes. If they are produced gradually in 

 response to slight changes in the environment, they will not 

 throw the individual out of harmony with it, which any sudden 

 large change must very frequently, if not always, do. Prof. 

 Thomson lays great stress upon the criticism that the theory 

 that evolution has been due to the selection of small variations 

 " places such a heavy burden on the shoulders of natural selec- 

 tion that the idea of a leaping instead of a creeping Proteus has 

 always been welcome." But to me the burden appears to 

 remain the same, whether the intermediate links were produced 

 in the process of species making or afterwards, for they have 

 been produced in either case. 



Whilst then the gradual small change in characters appears 

 to offer so many advantages, the utility of sudden and large 

 changes seems so highly problematical and this hypothesis 

 seems so much in the nature of an intellectual " mutation " on 

 insufficient grounds that I am not inclined to accept it. 



1 Materials for the Study of Variation, p. 17 (London, 1894). 



