THEORIES OF ORGANIC EVOLUTION 



direction. Regulated in their unions by the pleasure 

 or caprice of their masters, the almost endless varieties 

 of dogs differ from one another in color, in length, and 

 abundance of hair, which is sometimes entirely want- 

 ing ; in their natural instincts ; in size, which varies in 

 measure as one to five, mounting in some instances to 

 more than a hundredfold in bulk ; in the form of their 

 ears, noses, and tails ; in the relative length of their legs ; 

 in the progressive development of the brain, in several 

 of the domesticated varieties occasioning alterations 

 even in the form of the head, some of them having long, 

 slender muzzles with a flat forehead, others having 

 short muzzles with a forehead convex, etc., insomuch 

 that the apparent difference between a mastiff and a 

 water-spaniel and between a greyhound and a pug- 

 dog are even more striking than between almost any 

 of the wild species of a genus. 



"It follows from these observations that animals 

 have certain fixed and natural characters which resist 

 the effects of every kind of influence, whether proceed- 

 ing from natural causes or human interference ; and we 

 have not the smallest reason to suspect that time has 

 any more effect on them than climate. 



" I am aware that some naturalists lay prodigious 

 stress upon the thousands which they can call into 

 action by a dash of their pens. In such matters, how- 

 ever, our only way of judging as to the effects which 

 may be produced by a long period of time is by multi- 

 plying, as it were, such as are produced by a shorter 

 time. With this view I have endeavored to collect all 

 the ancient documents respecting the forms of animals ; 



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