Chap. VII. OF NATURAL SELECTION. 227 



lire or instinct to its proc^ony. It may well be asked how is 

 it possible to reconcile this case with the theory of natural 

 selection ? 



First, let it be remembered that wc have innumeral)le in- 

 stances, both in our domestic productions and in those in a 

 state of nature, of all sorts of differences of inherited structure 

 which are correlated with certain ages, and with either sex. 

 We have differences correlated not only Avith one sex, but 

 with that short period when the reproductive system is active, 

 as in the nuptial plumage of many birds, and in the hooked 

 jaws of the male salmon. We have even slight differences in 

 the horns of diQ'erent breeds of cattle in relation to an artifi- 

 cially imperfect state of the male sex ; for oxen of certain 

 breeds have longer horns than tlie oxen of other breeds, rela- 

 tively to the h'ugth of the horns in both the bulls and cows of 

 these same breeds. Hence I can see no great difficulty in any 

 character becoming correlated with the sterile condition of 

 certain members of insect communities : the difficulty lies in 

 understanding how such correlated modifications of structure 

 could have been slowly accumulated by natural selection. 



Tliis dilficulty, though ajipearing insuperable, is lessened, 

 ' or, as I believe, disajjpears, when it is remembered that selec- 

 tion may l)e applied to the family, as well as to the individual, 

 and may thus gain the desired end. Thus, breeders of cattle 

 wish the flesh and fat to be well marbled together ; the animal 

 has been slaughtered, but the breeder has gone witli confidence 

 to the same stock and has succeeded. Such faith may be 

 placed in the power of selection, that probably a breed of 

 cattle, always yielding oxen Avith extraordinarily long horns, 

 could be slowly formed by carefully Avatching Avhich individual 

 bulls and cows, Avhen matched, produced oxen Avith the longest 

 horns ; and yet no one ox Avould ever have propagated its 

 kind. Here is a better and real illustration : according to M. 

 Vcrlot, some varieties of the double annual stock of various 

 colors, from having been long carefully selected to the right 

 degree, always produce by seed a large projinrtion of plants 

 l)earing double andf|nite sterile floAvers ; so that, if the A'ariety 

 had not likewise yielded others, it Avould at once have become 

 extinct; but it always yields some single and fertile plants, 

 Avhich differ from ordinary single A'arieties only in their power 

 of producing the two forms. Thus the fertile plants producing 

 single flowers may be compared Avith the males and females of 

 an ant-comnumity, and the sterile double-flowered plants, Aviiich 



