204 THE GENESIS OF SPECIES. [CHAP. 



Though Mr. Darwin has not as yet expressly advocated 

 this view, yet some remarks made by him appear to show 

 his disposition to sympathize with it. Thus in his work 

 on " Animals and Plants under Domestication," 2 he asserts 

 that " the savages of Australia and South America hold the 

 crime of incest in abhorrence ; " but he considers that this 

 abhorrence has probably arisen by "Natural Selection," 

 the ill effects of close interbreeding causing the less numer- 

 ous and less healthy offspring of incestuous unions to dis- 

 appear by degrees, in favor of the descendants (greater 

 both in number and strength) or individuals who naturally, 

 from some cause or other, as he suggests, preferred to mate 

 with strangers rather than with close blood-relations ; this 

 preference being transmitted and becoming thus instinc- 

 tive, or habitual, in remote descendants. 



But on Mr. Darwin's own ground, it may be objected 

 that 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 insure 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 pos- 

 sessing the required " slight feeling," must give rise to off- 

 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 ex- 

 ample, he tells us: 3 "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 of parents 



2 Vol. ii., p. 122. 



8 "Animals and Plants under Domestication," vol. i., p. 295. 



