NATURAL SELECTION. 75 



in a state of nature natural selection will be enabled to act 

 on and modify organic beings at any age, by the accumula- 

 tion of variations profitable at that age, and by their inher- 

 itance at a corresponding age. If it profit a plant to have 

 its seeds more and more widely disseminated hj the wind, 

 I can see no greater difficulty in this being effected through 

 natural selection, than in the cotton-planter increasing and 

 improving by selection the down in the pods on his cotton- 

 trees. Natural selection may modify and adapt the larva of 

 an insect to a score of contingencies, wholly different from 

 those which concern the mature insect ; and these modifica- 

 tions may affect, through correlation, the structure of the 

 adult. So, conversely, modifications in the adult may affect 

 the structure of the larva ; but in all cases natural selection 

 will insure that they shall not be injurious : for if they were 

 so, the species would become extinct. 



Natural selection will modify the structure of the young 

 in relation to the parent, and of the parent in relation to 

 the young. In social animals it will adapt the structure of 

 each individual for the benefit of the whole community; 

 if the community profits by the selected change. What 

 natural selection cannot do, is to modify the structure of 

 one species, without giving it any advantage, for the good 

 of another species ; and though statements to this effect 

 may be found in works of natural history, I cannot find one 

 case which will bear investigation. A structure used only 

 once in an animal's 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 to the beak of 

 unhatched birds, used for breaking the eggs. 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 advantage, the process of modifica- 

 tion 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 thick- 

 ness of the shell being known to vary like every other 

 .structure. 



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



