10 VARIATION UNDER DOMESTICATION. [Chap. I 



doubts how strong is the tendency to inheritance ; that like pro- 

 duces like is his fundamental belief: doubts have been thrown on 

 this principle only by theoretical writers. When any deviation of 

 structure often 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, &c 3 appearing 

 in several members of the same family. If strange and rare 

 deviations of structure are really inherited, less strange and com- 

 moner 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 different 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 ances- 

 tor ; 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 

 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, ia 

 that, at whatever period of life a peculiarity first appears, it tends 

 to re-appear in the offspring at a corresponding age, though some- 

 times eariier. In many cases this could not be otherwise ; thus 

 the inherited peculiarities 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 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 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 confined to the 

 first appearance of the peculiarity, and not to the primary cause 



