34 ORIGIN OF SPECIES 



but naturalists differ 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 differ- 

 ence 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 

 bulldog, which 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 immuta- 

 bility of the many closely allied natural species — for in- 

 stance, 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 domestication ; 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 domesticated 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 domes- 

 tication 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 domesticated productions; but how 

 could a savage possibly know, when he first tamed an ani- 

 mal, whether it would vary in succeeding generations, and 

 whether it would endure other climates? Has the little 

 variability of the ass and goose, or the small power of en- 

 durance of warmth by the reindeer, or of cold by the com- 

 mon camel, prevented their domestication? I cannot doubt 

 that if other animals and plants, equal in number to our 

 domesticated productions, and belonging to equally diverse 

 classes and countries, were taken from a state of nature, 

 and could be made to breed for an equal number of genera- 



