198 MENTAL EVOLUTION IN ANIMALS. 



But the force or influence of heredity in the domain of 

 instinct (whether of the primary or secondary class) is per- 

 haps most strongly manifested in the effects of crossing. It 

 is not, indeed, easy to obtain this class of evidence in the 

 case of wild species, because hybrid forms in a state of nature 

 are rare. But when a wild species is crossed with a tame 

 one, it usually happens that the hybrid or mongrel progeny 

 present a blended psychology. And still more cogent is the 

 evidence of such blending when two different breeds of 

 domesticated animals are crossed, having diverse hereditary 

 habits, or as Mr. Darwin calls them, " domestic instincts." 

 Thus a cross-breed between a setter and a pointer will blend 

 the movements and habits of working peculiar to these two 

 breeds; Lord Alford's celebrated strain of greyhounds ac- 

 quired much courage from a single cross wdth a bull-dog ; * 

 and a cross with a beagle " generations back will give to a 

 spaniel a tendency to hunt hares."t 



Again, Knight says : — " In one instance I saw a very 

 young dog, a mixture of the Springing Spaniel and Setter, 

 which dropped upon crossing the track of a Partridge, as its 

 male parent w^ould have done, and sprang the bird in silence ; 

 but the same dog, having a couple of hours afterwards found 

 a Woodcock, gave tongue very freely, and just as its female 

 parent would have done. Such cross-bred animals are, how- 

 ever, usually worthless, and the experiments and observations 

 I have made upon '1 ein have not been very numerous or 

 interesting." 



On this point Mr. Darwin writes: — "These domestic 

 instincts, when thus tested by crossing, resemble natural 

 instincts, which in like manner become curiously blended 

 together, and for a long time exhibit traces of the instincts of 

 either parent ; for example, Le Eoy describes a dog, whose 

 great-grandfather w^as a wolf, and this dog showed a trace of 

 its wild parentage only in one way, by not coming in a 

 straight line to his master when called.":]: Some further 

 remarks on this subject will be found in Mr. Darwin's 

 appended essay on instinct ; and here I may fitly conclude 

 the present chapter by quoting the following paragraph 

 which occurs in another part of his MSS. 



* Youatt on Dog, p. 311. 



t Blaine, Rural Sports, p. 863, quoted by Darwin. 



X Origin of Specie-t, p. 210. 



