STABILITY OF THE GENE 299 



selection in the direction of the selection; sometimes 

 abruptly, as in the case of our 'mutant' race, a highly 

 stable plus variation ; but much of tener gradually, as has 

 occurred continuously in both the plus and the minus 

 selection series." 



In the following year he said : ' ' Many students of ge- 

 netics at present regard unit-characters as unchangeable. 

 . . . For several years I have been investigating this 

 question, and the general conclusion at which I have 

 arrived is this, that unit-characters are modifiable as well 

 as recombinable. Many Mendelians think otherwise, but 

 this is, I believe, because they have not studied the ques- 

 tion closely enough. The fact is unmistakable that unit- 

 characters are subject to quantitative variation. . . . 

 Selection, as an agency in evolution, must then be re- 

 stored to the important place which it held in Darwin's 

 estimation, an agency capable of producing continuous 

 and progressive racial changes." 



A careful reading of Darwin's books will fail to fur- 

 nish a single clear statement to the effect that he believed 

 that the selection process determines or influences the 

 direction of future variation, unless we bring into the 

 field another theory held by Darwin, namely, the theory 

 of inheritance of acquired characters. 



Darwin held strongly to the belief in Lamarck's theory. 

 He did not hesitate to make use of it whenever his theory 

 of natural selection was in difficulty. It would be logical, 

 therefore, for anyone who cared to do so (although Dar- 

 Avin himself does not appear to have put the two views 

 together, nor does Castle) to point out that whenever a 

 more advantageous type is selected its germ-cells are 

 exposed, so to speak, to the pangenes produced by its own 

 body, and might be expected to be changed in the direc- 

 tion of the character selected. Hence each new advance 

 would start from a new base, and if scattering variations 



