33 THE EVOLUTION THEORY 



have at the present day no fewer than seven main breeds, each of 

 which has its sub-brfeeds, often numerous. Thus there are forty-eight 

 sub-breeds which are used as guardians of our houses, ' house-dogs ' 

 in the restricted sense, thirty sub-breeds of dogs with silk-like hair 

 (King Charles dogs, Newfoundland dogs, &c.), twelve of terriers, 

 and thirty-five of sporting dogs, among them such different forms 

 as the deerhound and the pointer. We have further nineteen sub- 

 breeds of bulldogs, thirty-five of greyhounds, and six of naked or hair- 

 less dogs. Not only the main breeds, but even the sub-breeds often 

 differ as markedly from one another as wild species do, and the 

 question must first be decided whether each of the very distinct 

 breeds has not a special wild species as ancestor. 



Obviously, however, this cannot be maintained, for so many 

 species of wild dog have never existed on the earth at any time. We 

 know, too, that 4,000 or 5,000 years ago a large number of breeds 

 of dogs were in existence in India and Egypt. There were Pariah 

 dogs, coursers, greyhounds, mastiffs, house-dogs, lapdogs and terriers. 

 It is not possible that the products of all lands could, at that time, 

 have been gathered into one, and it is inconceivable that so many 

 wild species could have existed in the one country of India. 



On the other hand, however, it cannot be maintained that all 

 our present breeds have descended from a single wild species ; it is 

 much more probable that several wild species were domesticated in 

 different countries. 



It has often been supposed that the manifold diversity of our 

 present breeds has been brought about by crossing the various tamed 

 species. That cannot be the case, however, because crossing gives 

 rise only to hybrid mongrel forms, not to distinct breeds with quite 

 new characters. It is true that all breeds of dogs can be very readily 

 crossed with each other, but the result is not new breeds, but those 

 numberless and transient intermediate forms which the dog-breeder 

 despises as worthless for his purpose. It must therefore have been 

 through the influence of domestication, combined with crossing, that 

 a few wild species gave rise to the various breeds of dogs. 



The pedigree of the horse is rather more clear than that of 

 the dog. Even in this ease, indeed, one cannot definitely name 

 the ancestral wild form, but it is very probable that it was of a grey- 

 brown colour, and similar to the wild horses of our own day. Darwin 

 supposes that it must also have had the black stripe on the back 

 which is exhibited by the domestic ass, and by several wild species of 

 ass, basing his opinion on the fact that the spinal stripe often occurs 

 in foals, especially in those of a grey -brown colour. 



