CHARLES DARWIN 233 



life, if of high importance to it, might be modified to any extent by 

 natural selection; for instance, the great jaws possessed by certain 

 insects, used exclusively for opening the cocoon — or the hard tip of 

 the beak of unhatched birds, used for breaking the egg. It has been 

 asserted, that of the best short-beaked tumbler-pigeons a greater 

 number perish in the egg than are able to get out of it; so that 

 fanciers assist in the act of hatching. Now if nature had to make 

 the beak of a full-grown pigeon very short for the bird's own ad- 

 vantage, the process of modification would be very slow, and there 

 would be simultaneously the most rigorous selection of all the young 

 birds within the egg, which had the most powerful and hardest beaks, 

 for all with weak beaks would inevitably perish; or, more delicate 

 and more easily broken shells might be selected, the thickness of 

 the shell being known to vary like every other structure. 



It may be well here to remark that with all beings there must be 

 much fortuitous destruction, which can have little or no influence on 

 the course of natural selection. 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 conditions, must be annually 

 destroyed by accidental causes, which would not be in the least degree 

 mitigated by certain changes of structure or constitution which would 

 in other ways be beneficial to the species. But let the destruction 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 part are developed, — yet of those which do survive, the 

 best adapted individuals, supposing that there is any variability in a 

 favourable direction, will tend to propagate their kind in larger num- 

 bers than the less well adapted. If the numbers be wholly kept down 

 by the causes just indicated, as will often have been the case, natural 

 selection 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 reason to suppose that many species 



