10 VARIATION UNDER DOMESTICATION. [CHAP. 



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 ancestor ; why : 

 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 exclu- 

 sively or in a much greater degree, to the males alone. A much 

 more important rule, which I think maybe trusted, is that, at what- 

 ever 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 offspring 

 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 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 which may have acted on 

 the ovules or on the male element ; in nearly the same manner as 

 the increased length of the horns in the offspring from a short- 

 horned cow by a long-horned bull, though appearing late in life, is 

 clearly due to the male element. 



Having alluded to the subject of reversion, I may here refer to a 

 statement often made by naturalists namely, that our domestic 

 varieties, when run wild, gradually but invariably revert in cha- 

 racter to their aboriginal stocks. Hence it has been argued that no 

 deductions can be drawn from domestic races to species in a state 

 of nature. I have in vain endeavoured to discover on what decisive 

 facts the above statement has so often and so boldly been made. 

 There would be great difficulty in proving its truth : we may safely 

 conclude that very many of the most strongly marked domestic 

 varieties could not possibly live in a wild state. In many cases we 

 do not know what the aboriginal stock was, and so could not tell 

 whether or not nearly perfect reversion had ensued. It would be 

 necessary, in order to prevent the effects of intercrossing, that only 

 a single variety should Ks-ve been turned loose in its new home. 

 Nevertheless, as our varieties certainly do occasionally revert in 



