ORIGIN OF SPECIES. 137 



6. As these young are none of them exactly alike in all 

 respects, a process of " Natural Selection " will ensue, where- 

 by those individuals which possess any variation, however 

 slight, favourable to the peculiarities of the species, will tend 

 to be preserved. Those individuals, on the other hand, 

 which do not possess any such favourable variation, will be 

 placed at a disadvantage in the " struggle for existence," and 

 will tend to be gradually exterminated. The individuals, 

 therefore, composing any species, are thus subjected to a 

 rigid process of sifting, by which those least adapted to 

 their environment are being perpetually weeded out, whilst 

 " the survival of the fittest " is secured. 



7. Other conditions remaining the same, the individuals 

 which survive in the struggle for existence will transmit the 

 variations, to which they owe their preservation, to future 

 generations. 



8. By a repetition of this process, " varieties " are first 

 established ; these become permanent, and " races " are 

 produced ; finally, in the lapse of time, the differences thus 

 caused become sufficiently marked to constitute distinct 

 " species." 



9. If we grant that past time has been practically infinite, 

 it is conceivable that all the different animals and plants 

 which we see at present upon the globe, may have been 

 produced by the' action of Natural Selection upon the off- 

 spring of a few primordial forms, or, it may be, of a single 

 primitive being. 



Originally, Mr Darwin appears to have believed that 

 " Natural Selection " would alone be found to be a suffi- 

 cient cause to have given rise to all existing species by a 

 process of Evolution from pre-existing forms. In view, 

 however, of certain objections which had been brought for- 

 ward, Mr Darwin seems to have abandoned this position ; 

 and a cause supplementary to " Natural Selection " was 

 sought for in what Mr Darwin terms " Sexual Selection." 

 The action of Sexual Selection in a supposed process of 



