44 VARIATION. 



which have them from those which lack them. Our example of 

 the gene which distinguishes "fade" from full black mice leads 

 over to the case where a gene had no influence whatever. This 

 same gene, which certainly has an appreciable influence on the 

 colour of agouti mice, but very little on black ones, certainly 

 has no influence on silver-fawn animals, as far as I could de- 

 tect. All this shows, that a gene does not "determine" any 

 character, but that it tends to influence certain definite devel- 

 opmental processes, and that, if these same processes do not 

 take place for any reason, the gene has no influence. But this 

 is something quite different from the assumption, that such a 

 gene is transmitted in a state, which differs from the normal. 



The gene itself is not latent, or dormant, or weakened in any 

 way, for it can remain without influence throughout a number 

 of generations and be as active as ever as soon as it finds the 

 reaction which it influences. If we see that normal chickens 

 give a minority of off-spring with drooping tails, we may as- 

 sume that these normal chickens have a gene more than those 

 with the drooping tail. We can imagine how this gene, which 

 with other things seems to be necessary to make an otherwise 

 drooping tail grow erect, can be transmitted even if the tail 

 of all the chicks is cut off, or if the tail itself is wanting for some 

 other reason. One of us observed a brood of young chicks of 

 which the father was rumpless and the mother had a drooping 

 tail, and which grew up with normal, erect tails. 



The naive idea, that every character or every organ has its 

 own "determinant", makes it necessary to assume that in 

 certain cases in which the characters or organs were not forth- 

 coming, whereas the "determinant" was present (proved by 

 crossing-experiments) this determinant was dormant or latent. 

 I look upon the characters of an organism as upon the result 

 of the whole development, and upon the development as the 

 result of an enormous number of different factors of different 

 kind. 



For the production of bread in a bakery, a number of fact- 

 ors are necessary. We need a number of materials, flour, yeast, 



