32 EVOLUTION OF TO-DAY. 



But the evolutionist says that these are the only 

 limits. He tells us, moreover, that in most cases 

 these physical limits are so distant that there is 

 abundant opportunity for many new species to arise 

 before they are reached. 



But those who believe in special creation, and at 

 least one prominent naturalist who accepts evolu- 

 tion, claim that there are other limits. These limits 

 are internal and form the boundary line between 

 species. Animals may, it is said, vary in any direc- 

 tion within these limits, but can never exceed them. 

 A pigeon may vary very much, but it never ceases 

 to be a pigeon. Simple variation can never produce 

 a new species, but only varieties of the old species. 

 And this brings us to the real subject of this chap- 

 ter the immutability of species. 



Are Species Stable? 



The question we are to consider is this : Can 

 variations, by continual accumulations, become so 

 great as to form new species ; or are there boundary 

 lines between species beyond which variation cannot 

 extend ? 



What is a species ? Can this term be so accurately 

 defined as to make it possible to decide whether the 

 variations occurring are always within the limits of 

 the species, or whether they may not exceed them ? 



The answer to this question is, unfortunately, No. 

 Naturalists are unable to tell us what a species is 

 and what a variety. The greatest confusion exists 

 in the various systems of classification. No two 

 systematists agree as to their classification. Forms 



