Chap. IV.] RESULTS OF NATURAL SELECTION. 125 



profitable variations, will compensate for a lesser amount 

 of variability in each individual, and is, I believe, a 

 highly important element of success. Though Nature 

 grants long periods of time for the work of natural selec- 

 tion, she does not grant an indefinite period; for as all 

 organic beings are striving to seize on each place in the 

 economy of nature, if any one species does not become 

 modified and improved in a corresponding degree with 

 its competitors, it will be exterminated. Unless fa- 

 vourable variations be inherited by some at least of the 

 offspring, nothing can be effected by natural selection. 

 The tendency to reversion may often check or prevent 

 the work; but as this tendency has not prevented man 

 from forming by selection numerous domestic races, 

 why should it prevail against natural selection? 



In the case of methodical selection, a breeder selects 

 for some definite object, and if the individuals be al- 

 lowed freely to intercross, his work will completely fail. 

 But when many men, without intending to alter the 

 breed, have a nearly common standard of perfection, and 

 all try to procure and breed from the best animals, im- 

 provement surely but slowly follows from this uncon- 

 scious , process of selection, notwithstanding that there 

 is no separation of selected individuals. Thus it will be 

 under nature; for within a confined area, with some 

 place in the natural polity not perfectly occupied, all the 

 individuals varying in the right direction, though in 

 different degrees, will tend to be preserved. But if the 

 area be large, its several districts will almost certainly 

 present different conditions of life; and then, if the 

 same species undergoes modification in different dis- 

 tricts, the newly-formed varieties will intercross on the 

 confines of each. But we shall see in the sixth chapter 



