INSTINCT 233 



structure or instinct to its progeny. It may well be asked how it is 

 possible to reconcile this case with the theory of natural selection? 



First, let it be remembered that we have innumerable instances, 

 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 cor- 

 related not only with 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 different breeds of cattle in rela- 

 tion to an artificially imperfect state of the male sex, for oxen of 

 certain breeds have longer horns than the oxen of other breeds, 

 relatively to the length 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 understand- 

 ing how such correlated modifications of structure could have been 

 slowly accumulated by natural selection. 



This difficulty, though appearing insuperable, is lessened, or, as 

 I believe, disappears, when it is remembered that selection may be 

 applied to the family, as well as to the individual, and may thus 

 gain the desired end. Breeders of cattle wish the flesh and fat to be 

 well marbled together. An animal thus characterized has been 

 slaughtered, but the breeder has gone with confidence to the same 

 stock and has succeeded. Such faith may be placed in the power of 

 selection, that a breed of cattle always yielding oxen with extraor- 

 dinarily long horns, could, it is probable, be formed by carefully 

 watching which individual bulls and cows, when matched, pro- 

 duced oxen with the longest horns; and yet no one ox would ever 

 have propagated its kind. Here is a better and real illustration: 

 According to M. Verlot, some varieties of the double annual stock, 

 from having been long and carefully selected to the right degree, 

 always produces a large proportion of seedlings bearing double 

 and quite sterile flowers, but they likewise yield some single and 

 fertile plants. These latter, by which alone the variety can be 

 propagated, may be compared with the fertile male and female 

 ants, and the double sterile plants with the neuters of the same 

 community. As with the varieties of the stock, so with social in- 

 sects, selection has been applied to the family, and not to the in- 

 dividual, for the sake of gaining a serviceable end. Hence, we may 

 conclude that slight modifications of structure or of instinct, cor- 

 related with the sterile condition of certain members of the com- 

 munity, have proved advantageous; consequently the fertile males 



