THE EVIDENCE FROM DEGENERATION. 



347 



favoured change, and which saw copious modification and progression 

 in other groups of animals, might at first sight be regarded as present- 

 ing a serious obstacle to the doctrine of progressive development on 

 which the whole theory of evolution depends. As such an obstacle, 

 the series of facts in question was long regarded. In this light these facts 

 are sometimes even now advanced, but only by those who imperfectly 

 appreciate and only partially understand what the doctrine of evolu- 

 tion teaches and what its leading idea includes. Even Cuvier him- 

 self, when advancing the case of the apparently unchanged mummies 

 of Egyptian animals against Lamarck's doctrine of descent, failed 

 possibly through the imperfectly discussed stage in which the whole 

 question rested in his day to understand that the very facts of 

 preservation revealed in the monuments of Egypt testified to the 



FIG. 247. PEARLY NAUTILUS. 



absence of those physical changes which could alone have affected 

 the animals of the Nile land. But the fuller consideration of that 

 theory of nature which credits progressive change as the usual way of 

 life, shows us that it is no part of evolution to maintain either that 

 living beings must needs undergo continual change, or that they 

 must change and modify at the same rate. On the contrary, Mr. 

 Darwin, in his classic work, maintains exactly the opposite propo- 

 sition. There are, in fact, two great factors at work in living nature 

 a tendency to vary and change, and the influence of environments or 

 surroundings. Given the first tendency, which is not at all a matter of 

 dispute, the influence of the second is plainly enough discernible in 

 bringing to the front either the original, primitive, or, as it might be 

 named, the parent form, or the varying forms which are produced by 

 modification of the parent. As it has well been put : " Granting the 



