Chap. I.J CHARACTER OF DOMESTCC VAEIETIES. 19 



much in determining what characters are of generic 

 value ; all such valuations being at present empirical. 

 When it is explained how genera originate under 

 nature, it will be seen that we have no right to expect 

 often to find a generic amount of difference in our 

 domesticated races. 



In attempting to estimate the amount of structural 

 difference between allied domestic races, we are soon 

 involved in doubt, from not knowing whether they are 

 descended from one or several parent species. This 

 point, if it could be cleared up, would be interesting ; 

 if, for instance, it could be shown that the greyhound, 

 bloodhound, terrier, spaniel, and bull-dog, winch we 

 all know propagate their kind truly, were the offspring 

 of any single species, then such facts would have great 

 weight in making us doubt about the immutability of 

 the many closely allied natural species — for instance, 

 of the many foxes — inhabiting different quarters of the 

 world. I do not believe, as we shall presently see, that 

 the whole amount of difference between the several 

 breeds of the dog has been produced under domesti- 

 cation ; I believe that a small part of the difference is 

 due to their being descended from distinct species. In 

 the case of strongly marked races of some other domes- 

 ticated species, there is presumptive or even strong 

 evidence, that all are descended from a single wild 

 stock. 



It has often been assumed that man has chosen for do- 

 mestication animals and plants having an extraordinary 

 inherent tendency to vary, and likewise to withstand 

 diverse climates. I do not dispute that these capacities 

 have added largely to the value of most of our domes- 

 ticated productions • but how could a savage possibly 



