ZOOGENESIS 



we cannot make any really definite statement about 

 their ancestry. 



But regarding bull-dogs, pugs and hairless dogs we 

 can say with reasonable certainty that they do not 

 intergrade, and also that there are now no intergrades, 

 and there never have been any intergrades, between 

 these and any other types of dogs, or wolves. 



They therefore furnish an excellent and obvious 

 illustration of unbroken continuity of descent, from 

 wolves through other types of dogs, which is coupled 

 with abrupt change or discontinuity in bodily form 

 and in mental attributes. So far as we know, the 

 greyhounds, the hounds, and many other forms of 

 dogs had a similarly abrupt and discontinuous origin. 



The question naturally arises, is it permissible to 

 use the domestic dogs to illustrate the course of 

 animal evolution during geologic time? 



It is generally agreed that the changes in animal 

 life which took place from one geological epoch to 

 another occurred as a response to changes in the en- 

 vironment of the animals concerned — in other words 

 to changes in the conditions any given animal type 

 was forced to meet. Varieties or forms which were 

 best suited to meet the new conditions survived, and 

 the rest died out. The successful varieties or forms, 

 in the absence of competition, branched out into many 

 different forms which became more and more distinct 

 from each other until, with further geological 

 changes, most or all of these died out. 



Domestication means a change in the environment 

 of all animals which are subjected to its influence. 



[187] 



