890 THE ORIGIN OF SPECIES 



With these facts before me, I believe that natural 

 selection, by acting on the fertile ants or parents, could 

 form a species which shoulel regularly produce neuters, 

 all of large size with one form of jaw, or all of small 

 size with widely different jaws; or lastly, and this is the 

 greatest difficulty, one set of workers of one size and 

 structure, and simultaneously another set of workers of 

 a different size and structure; — a graduated series having 

 first been formed, as in the case of the driver ant, and 

 then the extreme forms having been produced in greater 

 and greater numbers, through the survival of the parents 

 which generated them, until none with an intermediate 

 structure was 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 wonder- 

 ful 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 labor is useful to civilized man. Ants, how- 

 ever, work by inherited instincts and by inherited organs, 

 or tools, while 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 



