GENERAL CONCLUSIONS 309 



but it would be extremely difficult, if not impossible, to 

 show that they do not arise. To the ancients it seemed not 

 incredible that worms and eels arose from the river's 

 slime, and that vermin in general arose in dark dusty 

 corners. The origin of bacterial life from putrefying sub- 

 stances was believed in only one generation ago, and it 

 was extremely difficult to prove that this does not happen. 

 It may be equally difficult to prove convincingly, to one 

 who insists on believing the contrary, that genes arise 

 independently of other genes ; but the genetic theory need 

 not be anxious concerning this question until it meets 

 with a situation where such a postulate becomes neces- 

 sary. At present we find no need of interpolating new 

 genes in the linkage series, or at the ends of the series. 

 If the same number of genes is present in a white blood 

 corpuscle as in all the other cells of the body that con- 

 stitutes a mammal, and if the former makes only an 

 amoeba-like cell and the rest collectively a man, it 

 scarcely seems necessary to postulate fewer genes for an 

 amoeba or more for a man. 



Are Genes of the Order of Organic Molecules? 



The only practical interest that a discussion of the 

 question as to whether genes are organic molecules might 

 have would relate to the nature of their stability. By 

 stability we might mean only that the gene tends to vary 

 about a definite mode, or we might mean that the gene is 

 stable in the sense that an organic molecule is stable. The 

 genetic problem would be simplified if we could establish 

 the latter interpretation. If, on the other hand, the gene 

 is regarded as merely a quantity of so much material, we 

 can give no satisfactory answer as to why it remains so 

 constant through all the vicissitudes of outcrossing, un- 

 less we appeal to mysterious powers of organization out- 

 side the genes that keep them constant. There is little 



