THEORY OF EVOLUTION 7 



tion is not necessary to account for such kinds 

 of histories. 



We are concerned here more particularly 

 with the biologists' ideas of evolution. My in- 

 tention is to review the evidence on which the 

 old theory rested its case, in the light of some 

 of the newer evidence of recent years. 



Four great branches of study have fur- 

 nished the evidence of organic evolution. They 

 are: 



Comparative anatomy. 



Embryology. 



Paleontology. 



Experimental Breeding or Genetics. 



The Evidence from Comparative Anatomy 

 When we study animals and plants we find 

 that they can be arranged in groups according 

 to their resemblances. This is the basis of com- 

 parative anatomy, which is only an accurate 

 study of facts that are superficially obvious to 

 everyone. 



The groups are based not on a single differ- 

 ence, but on a very large number of resem- 

 blances. Let us take for example the group of 

 vertebrates. 



