144 THE EVOLUTION THEORY 



concerned, as, for instance, in the broad-nosed breeds of dog — bull-dog 

 and pug-dog — we may refer the peculiar variation of many parts to 

 disturbances of the equilibrium of the determinant system, which 

 bring to light, not suddenly as in the case of saltatory variations, but 

 gradually and increasingly, the curious complex of characters. 

 Darwin referred such transformations of the whole animal facies, 

 where a single varying character is deliberately selected, to correla- 

 tion, and by this he understood the mutual influence of the parts of 

 an animal upon one another. Such correlation certainly exists, as we 

 have already seen in discussing histonal selection, but here we have 

 rather to do with the correlation of the parts of the germ-plasm, with 

 the efiects of germinal selection, which, aflected by the artificial 

 selection of particular characters, gradually brings about a more 

 marked disturbance in the whole determinant system. 



In the evolution of our breeds of domesticated animals, germinal 

 selection in the negative sense must also have played a part — I mean 

 through the weakening and degeneration of individual determinants. 

 Only in this way, it seems to me, can we explain the tameness of our 

 domestic animals, dogs, cats, horses, &c., in which all the instincts 

 of wildness, fleeing from Man, the inclination to bite, and to attack, 

 have at least partly disappeared. It is, of course, very difiicult to 

 estimate how much of this is to be ascribed to acquired habitude 

 during the individual lifetime. The case of the elephant might be 

 cited in evidence of tameness which arises in the individual lifetime, 

 for all tame elephants are caught wild, but it seems that captured 

 young beasts of prey, such as the fox, wolf, and wild cat, not to speak 

 of lions and tigers, never attain to the degree of tameness exhibited 

 by many of our domesticated dogs and cats. The very considerable 

 difierenees in the degree of tameness of dogs and cats go to show that 

 the case is one of instincts varying in different degree. 



If this be so, then the instinct of wildness, if I may express 

 myself so for the sake of brevity, has degenerated in consequence of 

 its superfluity, and through the process of germinal selection, which 

 allowed the determinants of the brain-parts concerned to set out on 

 a path of downward variation upon which they met with no 

 resistance on the part of personal selection. 



Herbert Spencer adduced against my position the case of the 

 reduction in the size of the jaws in many breeds of dog, especially in 

 pugs and other lap-dogs, which he regarded as evidence of the 

 inheritance of acquired characters. But this and analogous cases of 

 the degeneration of an organ during a long period in which the 

 animal had been withdrawn from the conditions of natural life is 



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