122 THEORY OF THE EARTH. 



ting and dispersing than the carnivorous species, 

 being influenced both by climate and by the kind 

 of nourishment which they need. 



Nature appears also to have guarded against the 

 alterations of species which might proceed from 

 mixture of breeds, by influencing the various species 

 of animals with mutual aversion from each other. 

 Hence all the cunning and all the force that man 

 is able to exert is necessary to accomplish such 

 unions, even between species that have the near- 

 est resemblances. And when the mule-breeds 

 that are thus produced by these forced con- 

 junctions happen to be fruitful, which is seldom 

 the case, this fecundity never continues beyond a 

 few generations, and would not probably proceed 

 so far, without a continuance of the same cares 

 which excited it at first. Thus we never see in 

 a wild state intermediate productions between 

 the hare and the rabbit, between the stag and the 

 doe, or between the martin and the weasel. But 

 the power of man changes this established order, 

 and contrives to produce all these intermixtures 

 of which the various species are susceptible, but 

 which they would never produce if left to them- 

 selves. 



The degrees of these variations are proportional 

 to the intensity of the causes that produce them, 

 namely, the slavery or subjection under which 

 those animals are to man. They do not proceed 



