ORIGIN OF SPECIES. 49 



respects, a process of " natural selection " will ensue, whereby 

 those individuals which possess any variation, however slight, 

 favourable to the peculiarities of the life 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, there- 

 fore, composing any species are thus subjected to a rigid pro- 

 cess of sifting, by which those least adapted to their environ- 

 ment 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 pro- 

 duced ; 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 sufficient 

 cause to have given rise to all existing species by a process of 

 evolution from pre-existing forms. In view, however, ot 

 certain objections which had been brought forward, 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 evolution, according to 

 Mr Darwin's views, may be stated in the following two pro- 

 positions : 



a. The males of many species of animals are known to 

 engage in very severe contests for the possession of the 

 females, these latter yielding themselves to the victor. In 

 such contests certain males will inevitably have certain advan- 

 tages over the others, either in point of strength or activity, 

 or in consequence of the possession of more efficient offensive 

 weapons. There will therefore always be a probability that 

 certain males will get possession of the females in preference 

 to others : and thus there will be a tendency in the individuals 



D 



