EFFECT OF NATURAL SELECTION 



93 



not only to develop still further their naturally valuable qualities, 

 but to bring about more or less radical readjustments occasioned 

 and made necessary by these new demands of ours. 



Natural selection always at work. We must not for a mo- 

 ment suppose that our domestication and the new standards of 

 breeding entirely do away with natural selection. In respect to 

 tooth and claw, of course selection stops the moment we make 

 warfare impossible, but in such 

 fundamental matters as constitu- 

 tional vigor, fecundity, and the 

 vital and reproductive faculties 

 natural selection never surren- 

 ders its hold upon a species. 



Ofttimes we forget this and 

 are brought up standing by the 

 consequences. Sometimes our 

 standards of selection are unwit- 

 tingly at opposites with these 

 fundamental matters, and then 

 the shock and the lesson are 

 severe. For instance, many an 

 amateur breeder will select the 

 fattest and smoothest pigs for 

 breeding purposes, not knowing 

 that these are neither the most 

 prolific nor the hardiest. His 



herd soon runs out. Natural selection has been at work day 

 and night to undermine his herd at the point of infertility. 



Some very favorite strains of cattle or sheep are decidedly 

 " shy breeders." If so, it may as well be understood that they 

 will go down under the relentless work of natural selection, 

 unless indeed the defect can be speedily remedied by finding 

 prolific strains among the favorites. 



Power of selection to modify type. Selection can do far 

 more than develop a single type to conform to some single 



Fig. 13. The passenger pigeon, 



wild parent of all the domesticated 



sorts that have been developed by 



selection (see Figs. 14 and 15) 



