I 



VARIATION UNDER DOMESTICATION 31 



appears, and we see it in the father and child, we cannot tell 

 whether it may not be due to the same cause having acted on 

 both ; but when amongst individuals, apparently exposed to 

 the same conditions, any very rare deviation, due to some 

 extraordinary combination of circumstances, appears in the 

 parent — say, once amongst several million individuals — and 

 it reappears in the child, the mere doctrine of chances almost 

 compels us to attribute its reappearance to inheritance. 

 Every one must have heard of cases of albinism, prickly 

 skin, hairy bodies, etc., appearing in several members of the 

 same family. If strange and rare deviations of structure are 

 really inherited, less strange and commoner deviations may 

 be freely admitted to be inheritable. Perhaps the correct 

 way of viewing the whole subject would be, to look at the 

 inheritance of every character whatever as the rule, and 

 non-inheritance as the anomaly. 



The laws governing inheritance are for the most part 

 unknown. No one can say why the same peculiarity in dif- 

 ferent individuals of the same species, or in different species, 

 is sometimes inherited and sometimes not so; why the child 

 often reverts in certain 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 commonly but not exclusively to the like sex. 

 It is a fact of some importance to us, that peculiarities ap- 

 pearing in the males of our domestic breeds are often trans- 

 mitted, 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 pecu- 

 liarities in the horns of cattle could appear only in the off- 

 spring when nearly mature ; peculiarities in the silkworm 

 are known to appear at the corresponding caterpillar or 

 cocoon stage. But hereditary diseases and some other facts 

 make me believe that the rule has a wider extension, 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 



