32 ORIGIN OF SPECIES 



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 aversion, I may here 

 refer to a statement often made by naturalists — namely, 

 that our domestic varieties, when run wild, gradually but 

 invariably revert in character 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 

 M-as, and so could not tell whether or not nearly perfect re- 

 version had ensued. It would be necessary, in order to pre- 

 vent the effects of intercrossing, that only a single variety 

 should have been turned loose in its new home. Neverthe- 

 less, as our varieties certainly do occasionally revert in some 

 of their characters to ancestral forms, it seems to me not 

 improbable that if we could succeed in naturalising, or were 

 to cultivate, during many generations, the several races, for 

 instance, of the cabbage, in very poor soil (in which case, 

 however, some effect would have to be attributed to the 

 definite action of the poor soil), that they would, to a large 

 extent, or even wholly, revert to the wild aboriginal stock. 

 Whether or not the experiment would succeed, is not of 

 great importance for our line of argument; for by the ex- 

 periment itself the conditions of life are changed. If it 

 could be shown that our domestic varieties manifested a 

 strong tendency to reversion, — that is, to lose their acquired 

 characters, whilst kept under the same conditions, and whilst 

 kept in a considerable body, so that free intercrossing might 



