96 ORIGIN OF SPECIES 



ations," it must never be forgotten that mere individual dif- 

 ferences are included. As man can produce a great result 

 with his domestic animals and plants by adding up in any 

 given direction individual differences, so could natural selec- 

 tion, but far more easily from having incomparably longer 

 time for action. Nor do I believe that any great physical 

 change, as of climate, or any unusual degree of isolation to 

 check immigration, Is necessary in order that new and un- 

 occupied places should be left, for natural selection to fill up 

 by improving some of the varying inhabitants. For as all 

 the inhabitants of each country are struggling together with 

 nicely balanced forces, extremely slight modifications in the 

 structure or habits of one species would often give it an ad- 

 vantage over others; and still further modifications of the 

 same kind would often still further increase the advantage, 

 as long as the species continued under the same conditions 

 of life and profited by similar means of subsistence and de- 

 fence. No country can be named in which all the native in- 

 habitants are now so perfectly adapted to each other and to 

 the physical conditions under which they live, that none of 

 them could be still better adapted or improved; for in all- 

 countries, the natives have been so far conquered by natural- 

 ised productions, that they have allowed some foreigners to 

 take firm possession of the land. And as foreigners have 

 thus in every country beaten some of the natives, we may 

 safely conclude that the natives might have been modified 

 with advantage, so as to have better resisted the intruders. 



As man can produce, and certainly has produced, a great 

 result by his methodical and unconscious means of selection, 

 what may not natural selection effect? Man can act only on 

 external and visible characters : Nature, if I may be allowed 

 to personify the natural preservation or survival of the fit- 

 test, cares nothing for appearances, except in so far as they 

 are useful to any being. She can act on every internal organ, 

 on every shade of constitutional difference, on the whole 

 machinery of life. Man selects only for his own good: Na- 

 ture only for that of the being which she tends. Every 

 selected character is fully exercised by her, as is implied by 

 the fact of their selection. Man keeps the natives of many 

 climates in the same country; he seldom exercises each se- 



