OBJECTIONS TO THE THEORY 295 



been produced in greater and greater numbers, through the 

 survival of the parents which generated them, until none 

 with an intermediate structure were produced. 



An analogous explanation has been given by Mr. Wallace, 

 of the equally complex case, of certain Malayan Butterflies 

 regularly appearing under two or even three distinct female 

 forms; and by Fritz Miiller, of certain Brazilian crustaceans 

 likewise appearing under two widely distinct male forms. 

 But this subject need not here be discussed. 



I have now explained how, as I believe, the wonderful fact 

 of two distinctly defined castes of sterile workers existing in 

 the same nest, both widely different from each other and from 

 their parents, has originated. We can see how useful their 

 production may have been to a social community of ants, on 

 the same principle that the division of labour is useful to 

 civilised man. Ants, however, work by inherited instincts 

 and by inherited organs or tools, whilst man works by 

 acquired knowledge and manufactured instruments. But I 

 must confess, that, with all my faith in natural selection, I 

 should never have anticipated that this principle could 

 have been efficient in so high a degree, had not the case of 

 these neuter insects led me to this conclusion. I have, there- 

 fore, discussed this case, at some little but wholly insufficient 

 length, in order to show the power of natural selection, and 

 likewise because this is by far the most serious special dif- 

 ficulty which my theory has encountered. The case, also, is 

 very interesting, as it proves that with animals, as with 

 plants, any amount of modification may be effected by the 

 accumulation of numerous, slight, spontaneous variations, 

 which are in any way profitable, without exercise or habit 

 having been brought into play. For peculiar habits confined 

 to the workers or sterile females, however long they might 

 be followed, could not possibly affect the males and fertile 

 females, which alone leave descendants. I am surprised that 

 no one has hitherto advanced this demonstrative case of 

 neuter insects, against the well-known doctrine of inherited 

 habit, as advanced by Lamarck. 



