214 THE GENESIS OF SPECIES. [Ciiap 



incestuous unions to disappear by degrees, in favour of the 

 descendants (greater both in number and strength) of indi- 

 viduals who naturally, from some cause or other, as he 

 sufjcjests, preferred to mate with stram^ers rather than with 

 close blood- relations; this preference being transmitted 

 and becoming thus instinctive, or habitual, in remote 

 descendants. 



But on ]\lr. Darwin's own ground, it maybe objected 

 tliat this notion fails to account for "abhorrence," and 

 " moral reprobation ; " for, as no stream can rise higher 

 than its source, the original " slight feeling " which was 

 useful would have been perpetuated, but would never have 

 been augmented beyond the degree requisite to ensure 

 this beneficial preference, and therefore would not certainly 

 have become magnified into " abhorrence." It will not 

 do to assume that the union of males and females, each 

 possessing the required " slight feeling," must give rise to 

 ott'spring with an intensified feeling of the same kind; for, 

 apart from reversion, Mr. Darwin has called attention to 

 the unexpected modifications which sometimes result from 

 the union of similarly constituted parents. Thus, for 

 example, he tells us : ^ "If two top-knotted canaries are 

 matched, the young, instead of having very fine top-knots, 

 are generally bald." From examples of this kind, it is 

 fair, on Darwinian principles, to infer that the union (if 

 parents who possessed a similar inherited aversion might 

 result in phenomena quite other than the augmentation of 

 such aversion, even if the two aversions should be alto- 

 gether of the same kind ; while, very probably, they might 

 be so different in their nature as to tend to neutralize each 

 other. Besides, the union of parents so similarly emotional 



* "Animals and riiints under Domestication," vol. i. \\. 205. 



