64 DARWINISM STATED BY DARWIN HIMSELF. 



forms of certain existing allied varieties, which have sup- 

 planted their early progenitors. 



UNKNOWN LAWS OP INHERITANCE. 



Origin of ^ ne ^ aws governing inheritance are for the 



Species, most part unknown. No one can say why the 

 page ' same peculiarity in different individuals of the 

 same species, or in different species, is sometimes inherited 

 and sometimes not so ; why the child often reverts in cer- 

 tain characters to its grandfather or grandmother or more 

 remote ancestor ; why a peculiarity is often transmitted 

 from one sex to both sexes, or to one sex alone, more com- 

 monly but not exclusively to the like sex. It is a fact of 

 some importance to us that peculiarities appearing in the 

 males of our domestic breeds are often transmitted either 

 exclusively, or in a much greater degree, to the males 

 alone. A much more important rule, which I think may 

 be trusted, is that, at whatever period of life a peculiarity 

 first appears, it tends to reappear in the offspring at a 

 corresponding age, though sometimes earlier. In many 

 cases this could not be otherwise : thus the inherited pe- 

 culiarities in the horns of cattle could appear only in the 

 offspring when nearly mature ; peculiarities in the silk- 

 worm are known to appear at the corresponding cater- 

 pillar or cocoon stage. But hereditary diseases and some 

 other facts make me believe that the rule has a wider ex- 

 tension, and that, when there is no apparent reason why 

 a peculiarity should appear at any particular age, yet that 

 it does tend to appear in the offspring at the same period 

 at which it first appeared in the parent. I believe this 

 rule to be of the highest importance in explaining the 

 laws of embryology. These remarks are, of course, con- 

 fined to the first appearance of the peculiarity, and not 



