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130 THE ORIGIN OF SPECIES 



there must be much fortuitous destraction, which can 

 have little or no influence on the course of natural selec- 

 tion. For instance, a vast number of eggs or seeds are 

 annually devoured, and these could be modified through 

 natural selection only if they varied in some manner 

 which protected them from their enemies. Yet many of 

 these eggs or seeds would perhaps, if not destroyed, have 

 yielded individuals better adapted to their conditions of 



^ life than any of those which happened to survive. So 

 again a vast number of mature animals 'and plants, 

 whether or not they be the best adapted to their condi- 

 tions, must be annually destroyed by accidental causes, 

 which would not be in the least degree mitigated by cer- 

 tain changes of structure or constitution which would in 

 other ways be beneficial to the species. But let the de- 

 struction of the adults be ever so heavy, if the number 

 which can exist in any district be not wholly kept down 

 by such causes — or again let the destruction of eggs or 



' , seeds be so great that only a hundredth or a thousandth 



i 



(' part are developed — yet of those which do survive, the 

 best adapted individuals, supposing that there is any wa,- 

 n\^ riability in a favorable direction, will tend to propagate 

 \> ,- their kind in larger numbers than the less well adapted. 

 (r If the numbers be wholly kept down by the causes just 



indicated, as will often have been the case, natural selec- 

 tion will be powerless in certain beneficial directions; but 

 this is no valid objection to its efficiency at other times 

 and in other ways; for we are far from having any rea- 

 son to suppose that many species ever undergo modifica- 

 tion and improvement at the same time in the same area. 



