196 



HABIT AND INTELLIGENCE. 



[chap. 



Inter- 

 mediate 

 breeds are 

 difficult to 

 obtain. 



Reversion 

 common 

 ill mixed 

 breeds. 



Otter 

 sheep. 



Variation 

 usually 

 slow 

 among 

 animals : 



often sud- 

 den among 

 plants. 



wear out, but appears to increase in the first few genera- 

 tions. When the breeds that are crossed are very different, 

 the variation is so great that it is nearly impossible to 

 obtain a permanent breed of character intermediate between 

 the two parent breeds.^ 



Mixture of race, which is thus a stimulus to variation, 

 also facilitates reversion to ancestral characteristics. Thus, 

 in all the domestic varieties of the pigeon, birds are occa- 

 sionally found that have reverted to the blue colour, with 

 black bars on the wings, and other characters of the wild 

 rock-pigeon, from Avhich the domestic breeds are descended ; 

 and such specimens are particularly abundant where the 

 breeds have been mixed.^ Sometimes, where very unlike 

 breeds have been mixed, the offspring are neither inter- 

 mediate between the parents nor irregularly variable ; but 

 some of them resemble one parent, and some the other. 

 Something of this is very common in families of children, 

 where some generally resemble the father's family, and 

 some the mother's. But the most remarkable instance I 

 know is that of the otter, or Ancon sheep, an accidental 

 variety that appeared at one time in North America, and 

 was preserved by the farmers, in consequence of its being 

 unable to leap fences. It began with a single lamb ; and 

 when the otter sheep were crossed with the common kind, 

 some of the lambs resembled the ram, and others the ewe ; 

 but no mixed breed was ever produced. 



Variation among animals is usually gradual, being but 

 slight in a single generation, though, under favourable cir- 

 cumstances, it may accumulate through successive genera- 

 tions. When it is considerable, as in the case of the 

 otter sheep just mentioned, it is usually in some degree 

 monstrous.^ Sudden variation is much commoner anions 

 plants, as in the case of " sporting " plants. The following 

 cases of the sudden origin of what appear to be permanent 



1 Darwin's Origin of Species, p. 21. ^ n,iQ_ p igg_ 



^ It is impossible to draw the line where mere variation ends and 

 monstrosity begins. A variation of a degree that would be called a 

 monstrosity in an animal, would be called only a "sport," or a singular 

 variety, in a plant. 



