308 THE THEORY OF THE GENE 



ad absurdum that that process has been a steady drain 

 on the original storehouse of genes wherever they existed. 



In chapter VI the genetic evidence at hand that bears 

 on this question has been considered, and it is unneces- 

 sary to summarize again what was there said, but I may 

 be allowed to repeat that it is not justifiable to conclude 

 from the fact that many mutant characters are defective, 

 or even partial or complete losses, that they must, there- 

 fore, be due to absences of a corresponding gene in the 

 germ material. So far as there is any direct evidence that 

 bears on this question, quite aside from the arbitrariness 

 of the absence hypothesis, it does not, as I have at- 

 tempted to show, support such a point of view. 



There remains, however, a problem of some interest, 

 namely, whether some or many of the changes in the 

 genes that lead to the occurrence of mutant characters 

 (whether recessive, intermediate, or dominant makes 

 little difference) may not be due to a breaking up of a 

 gene, or to its reconstitution into another element pro- 

 ducing somewhat different effects. There is, however, no 

 reason for assuming that such change, if it occurs, is a 

 downhill one rather than the development of a more com- 

 plex gene, unless it appears more probable, a priori, that 

 a highly complex stable compound is more likely to break 

 down than to build up. Until we know more concerning 

 the chemical constitution of the genes, and how they grow 

 and divide, it is quite futile to argue the merits of the two 

 sides of the argument. For the genetic theory it is only 

 necessary to assume that any kind of a change may suffice 

 as a basis for what is observed to take place. 



It is equally futile to discuss, at present, whether new 

 genes arise independently of the old ones, and worse than 

 futile to discuss how the genes arose in the first instance. 

 The evidence that we have furnishes no grounds whatso- 

 ever for the view that new genes independently arise, 



