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power to do, it must necessarily succumb and take its fate. Unless 

 its constitution can get accustomed to a warmer or colder, a drier 

 or wetter climate, or to some different food from what it has been 

 used to, or its young can be reared in some different way from 

 formerly with precautions against its coming to harm, or the 

 animal can contrive some new stratagems for evading its enemies, 

 as the case may be, it can never hold its place long where it is. 

 What evidence have we then to shew that with very many animals 

 there is that elasticity of constitution, if we may use the expression, 

 as opposed to anything rigid and unalterable in their nature, which 

 enables them to meet and get over the difficulty 1 We might 

 appeal in the first instance to the case of domestic animals, which, 

 from long living under the care and tutelage of man, have some of 

 them become so different in their habits and even in structural 

 characters, that we can no longer point with certainty to the stocks 

 from which they originally sprung ; as on the other hand, if after 

 long domestication, they are neglected and turned adrift, they lose 

 the characteristics they had acquired in their reclaimed state, and 

 gradually reassume their feral habits. 



Though not dii'ectly connected with our subject, it might be men- 

 tioned that it is the same with the Cerealia among plants. Either 

 the original stocks of some species have passed away altogether, or 

 they are become so metamorphosed by continued cultivation as to 

 be no longer recognizable. Here, too, cultivation being withheld, 

 the plants fall back in luxuriance and fertility, making probably an 

 approach to their original condition. 



But not to dwell upon the case of domestic animals we have 

 plenty of instances of changed instincts among the wild ones. 

 And it is worthy of note that many such changes must have 

 occurred in the case of species, which though not kept or cared for 

 by man have long attached themselves to his dwelling or its 

 immediate neighbourhood. Such are the rat and mouse, the house 

 sparrow, chimney swallow, and several others. The rat and the 

 mouse have been carried by man im wittingly all over the world. 

 The sparrow which now generally places its nest under the eaves 

 of buildings, no doubt in former ages built in trees, which it still 

 does occasionally, the nest in such cases being better constructed, 



