ly the Study of Domestic Animals. 191 



The distinguishing characters of races, which relate princi- 

 pally in the majority of cases to their colour and dimensions, are 

 in some species very marked and manifest at the first glance ; in 

 others they are observed with greater difficulty, and sometimes 

 can scarcely be discovered. These differences render the gene- 

 ral fact I have just been pointing out somewhat more difficult to 

 determine, but they do not in;iplidate it ; and an explanation of 

 them all may readily be deduced from considerations which are 

 in themselves sufficiently simple. In truth it is sufficient, on 

 the one hand, to think of the very many and great variations 

 which the animals present in their mode of life, and in their 

 habitat, to enable us to perceive that ihey should nc^'^-all be af- 

 fected in the same degree by the influence of climate, the topo- 

 graphical position, and the other local circumstances of the 

 country which they inhabit. On the other hand, observation re- 

 veals to us another cause which is somewhat more difficult to 

 foresee by means of reasoning, and which consists in differences 

 even of organization ; it is, however, true that some types resist 

 more, and others more readily yield to the influence of local cir- 

 cumstances, even when these last are, or at least appear to be, 

 precisely the same in both cases. 



To this opinion, then, that the wild species are variable under 

 the influence of different local circumstances, — that there exists 

 among them hereditary varieties or races as among domesticated 

 animals ; it is moreover necessary to add this other considera- 

 tion, viz. that they are variable in unequal degrees. Both of 

 these opinions are alike inconte&tible. But this inequality should 

 not prevent, and in fact does not, the existence in the limits of 

 variation peculiar to each species, a well determined relation be- 

 twixt the intensity of the modification and that of the differ- 

 ences under the influence of which they are produced. Here, 

 as in every other case, the effect is in the ratio of the cause, and 

 observation as well as theory authorizes us to regard in the wild 

 varieties the differences of the races as proportioned, other things 

 being equal, to the difference of the circumstances in the midst 

 of which the races subsist. 



The application of these sentiments regarding the hereditary 

 varieties or races of wild animals, to the hereditary varieties or 

 races of domesticated animals and to man, is both direct and 



