418 DARWINISM chap. 



not have been effected by " simultaneous fortunate spontaneous 

 variations." But this difficulty is fully disposed of by the 

 facts of simultaneous variation adduced in our third chapter, 

 and has also been specially considered in Chapter YI, p. 127. 

 The best answer to this objection may, perhaps, be found in 

 the fact that the very thing said to be impossible by variation 

 and natural selection has been again and again effected by 

 variation and artificial selection. Diu'ing the process of forma- 

 tion of such breeds as the greyhound or the bull-dog, of the 

 race-horse and cart-horse, of the fantail pigeon or the otter- 

 sheep, many co-ordinate adjustments have been produced ; and 

 no difficulty has occurred, whether the change has been effected 

 by a single variation — as in the last case named — or by slow 

 steps, as in all the others. It seems to be forgotten that most 

 animals have such a surplus of vitality and strength for all the 

 ordinary occasions of life that any slight superiority in one 

 part can be at once utilised ; while the moment any want of 

 balance occurs, variations in the insufficiently developed parts 

 will be selected to bring back the harmony of the Avhole 

 organisation. The fact that, in all domestic animals, variations 

 do occur, rendering them swifter or stronger, larger or smaller, 

 stouter or slenderer, and that such variations can be separately 

 selected and accumulated for man's purposes, is sufficient to 

 render it certain that similar or even greater changes may be 

 effected by natural selection, which, as Dar^\^n well remarks, 

 "acts on every internal organ, on every shade of constitu- 

 tutional difference, on the whole machinery of life." The 

 difficulty as to co-adaptation of parts by variation and natural 

 selection appears to me, therefore, to be a wholly imaginary 

 difficulty which has no place whatever in the operations of 

 nature. 



Direct Action of the Environment. 



JVIr. Spencer's last objection to the "^vide scope given by 

 Dar-\vinians to the agency of natural selection is, that organisms 

 are acted upon by the environment, which produces in them 

 definite changes, and that these changes in the indi^ddual are 

 transmitted by inheritance, and thus become increased in 

 successive generations. That such changes are produced in 

 the individual there is amjDle evidence, but that they are in- 



