230 OBJECTIONS TO THE THEORY [Chap. VIII. 



members of insect-communities : the difficulty lies in understanding 

 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 characterised 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 extra- 

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

 watching which individual bulls and cows, when matched, produced 

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

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

 ing to M. Verlot, some varieties of the double annual Stock from 

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

 produce 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 insects, selection 

 has been applied to the family, and not to the individual, for the 

 sake of gaining a serviceable end. Hence we may conclude that 

 slight modifications of structure or of instinct, correlated with the 

 sterile condition of certain members of the community, have proved 

 advantageous : consequently the fertile males and females have 

 flourished, and transmitted to their fertile offspring a tendency to 

 produce sterile members with the same modifications. This pro- 

 cess must have been repeated many times, until that prodigious 

 amount of difference between the fertile and sterile females of the 

 same species has been produced, which we see in many social 

 insects. 



But we have not as yet touched on the acme of the difficulty ; 

 namely, the fact that the neuters of several ants differ, not only 

 from the fertile females and males, but from each other, sometimes 

 to an almost incredible degree, and are thus divided into two or even 

 three castes. The castes, moreover, do not commonly graduate 

 into each other, but are perfectly well defined ; being as distinct 

 from each other as are any two species of the same genus, or rather 

 as any two genera of the same family. Thus in Eciton, there are 

 working and soldier neuters, with jaws and instincts extraordinarily 



