34 



THE AMERICAN NATURALIST [Yol. LYI 



The fact that the genes have this autocatalytic power 

 is in itself sufficiently striking, for they are undoubtedly 

 complex substances, and it is difficult to understand by 

 what strange coincidence of chemistry a gene can happen 

 to have just that very special series of physico-chemical 

 effects upon its surroundings which produces — «f all pos- 

 sible end-products— just this particular one, whicli is 

 identical with its own complex structure. But the most 

 remarkable feature of the situation is not this oft-noted 

 autocatalytic action in itself— it is the fact that, when the 

 structure of the gene becomes changed, through some 

 " chance variation," the catalytic property of the gene 

 may - become correspondingly changed, in such a way as 

 to leave it still aw^ocatalytic. In other words, the change 

 in gene structure— accidental though it was— has some- 

 how resulted in a change of exactly appropriate nature 

 in the catalytic reactions, so that the new reactions are 

 now accurately adapted to produce more material just 

 like that in the new changed gene itself. It is this para- 

 doxical phenomenon which is implied in the expression 

 " variation due to change in the individual gene," or, as 

 it is often called, " mutation." 



What sort of structure must the gene possess to permit 

 it to mutate in this way! Since, through change after 

 change in the gene, this same phenomenon persists, it is 

 evident that it must depend upon some general feature of 

 gene construction— common to all genes— which gives 

 each one a general autocatalytic power— a "carte 

 blanche "— io build material of whatever specific sort it 

 itself happens to be composed of. This general principle 

 of gene structure might, on the one hand, mean nothing 

 more than the possession by each gene of some very 

 simple character, such as a particular radicle or side- 

 chain "-alike in them all- which enables each gene to 

 enter into combination with certain liiirlily oruanized 

 materials in the outer protoplasm, in <u?-U n w;iy' a- to 

 result in the formation, " by " the i>i-<il npln^m /,f „,,)^.^, 

 material like this gene which'is in conibinat ion wit li it ' In 



