854 THE ORIGIN OF SPECIES 



are certaialy fur less fixed than natural instincts; but 

 tlie}' have been acted on by far less rigorous selection, 

 and have been transmitted for an incomparably shorter 

 period, under less fixed conditions of life. 



Uow strongly these domestic instincts, habits, and dis- 

 positions are inherited, and how curiously they become 

 mingled, is well shown when different breeds of dogs are 

 crossed. Thus it is known that a cross with a bulldog 

 has affected for many generations the courage and obsti- 

 nacy of greyhounds; and a cross with a greyhound has 

 given to a whole family of shepherd-dogs a tendency to 

 hunt hares. These domestic instincts, when thus tested 

 by crossing, resemble natural instincts, which in a like 

 manner become curiously blended together, and for a long 

 period exhibit traces of the instincts of either parent: for 

 example, Le Roy describes a dog, whose great-grandfather 

 was a wolf, and this dog showed a trace of its wild par- 

 entage only in one way, by not coming in a straight 

 line to his master when called. 



Domestic instincts are sometimes spoken of as actions 

 which have become inherited solely from long-continued 

 and compulsory habit; but this is not true. No one 

 would ever have thought of teaching, or probably could 

 have taught, the tumbler-pigeon to tumble — an action 

 which, as I have witnessed, is performed by young birds 

 that have never seen a pigeon tumble. We may believe 

 that some one pigeon showed a slight tendency to this 

 strange habit, and that the long-continued selection of the 

 best individuals in successive generations made tumblers 

 what they now are; and near Glasgow there are house 

 tumblers, as I hear from Mr. Brent, which cannot fly 

 eighteen inches high without going head over heels. It 



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