Chap. XXI. CARRIED TO AN* EXTREME. 227 



races. We can thus see how it is that race-horses and dray- 

 horses, greyhounds and mastiffs, which are opposed to each 

 other in every character, — how varieties so distinct as Cochin- 

 china fowls and bantams, or carrier-pigeons with very long 

 beaks, and tumblers with excessively short beaks, have been 

 derived from the same stock. As each breed is slowly im- 

 proved, the inferior varieties are first neglected and finally 

 lost. In a few cases, by the aid of old records, or from inter- 

 mediate varieties still existing in countries where other 

 fashions have pi'evailed, we are enabled partially to trace the 

 graduated changes through which certain breeds have passed. 

 Selection, whether methodical or unconscious, always tending 

 towards an extreme point, together with the neglect and slow 

 extinction of the intermediate and less-valued forms, is the 

 key which unlocks the mystery of how man has produced 

 such wonderful results. 



In a few instances selection, guided by utility for a single 

 purpose, has led to convergence of character. All the im- 

 proved and different races of the pig, as Nathusius has well 

 shown, 59 closely approach each other in character, in their 

 shortened legs and muzzles, their almost hairless, large, 

 rounded bodies, and small tusks. "We see some degree of 

 convergence in the similar outline cf the body in well-bred 

 cattle belonging to distinct races. 60 I know of no other such 

 cases. 



Continued divergence of character depends on, and is indeed 

 a clear proof, as previously remarked, of the same parts con- 

 tinuing to vary in the same direction. The tendency to mere 

 general variability or plasticity of organisation can certainly 

 be inherited, even from one parent, as has been shown by 

 Giirtner and Kolreuter, in the production of varying hybrids 

 from two species, of which one alone was variable. It is in 

 itself probable that, when an organ has varied in any manner, 

 it will again vary in the same manner, if the conditions which 

 first caused the being to vary remain, as far as can be judged, 

 the same. This is either tacitly or expressly admitted by all 



59 'Die Racen des Schweines,' 1860, head by M. de Quatrefages, 'Unite in 

 8. 48. l'Espece Humaine,' 1861, p. 119. 



hQ See some good remarks on this 



Q 2 



