68 SPECIES NOT 



the black grouse of peaty earth/' These act 

 as preservatives; they are exemplifications of 

 "natural selection." I pass over the fact that 

 4 'smooth-skinned fruits suffer more from beetles 

 than downy ones; and that purple plums are 

 less liable to disease than yellow ones," in order 

 that I may mention a modification of the utmost 

 importance to Mr. Darwin's theory, produced by 

 natural selection, namely, that "variations which 

 under domestication appear at any particular 

 period of life, tend to re-appear in the offspring 

 at the same period." 



Mr. Darwin hereafter founds some serious 

 arguments on this assumed power of natural 

 selection. It will also "modify the structure of 

 the young in relation to the parent, and of the 

 parent in relation to the young," but it cannot 

 "modify the structure of one species, without 

 giving it any advantage for the good of another 

 species." (Pages 86-7.) 



Further, "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, 

 as the great jaws of certain insects, used only 

 for opening the cocoon, or the hard tip to the 

 beak of nestling birds, used for breaking the 

 egg. Thus, if nature wanted to make (for the 

 bird's own advantage) the beak of a full-grown 

 pigeon very short, the process of modification 

 % would be very slow, and there would be simul- 

 taneously the most rigorous 'selection' of the 

 young birds within the egg which had the 



