Chapter III 



THE EYIDEXCE FOR ORGANIC 



EVOLUTIOX 



Four branches of study have furnished the evidence 

 of organic evolution: Com^^arative anatomy; Em- 

 bryology; Paleontology; and Experimental Breed- 

 ing or Genetics. 



The Evidence from Comparaiive 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 comparative anat- 

 omy, which is only an accurate study of facts that 

 are superficially obvious to everyone. 



The groups are based not on a single difference, 

 but on a very large number of resem])lances. Let us 

 take for example the group of vertebrates. 



The hand and the arm of man are similar to the 

 hand and arm of the ape {jig. 4) . The legs of man, 

 monkey, dog, sheep, and the horse are made up of 

 similar bones {jig, 5) . The same parts are found in 

 the leg of the lizard, the frog, and, even though less 

 certainly, in the fins of fishes. Comparsion does not 

 end here. We find similarities in the skull and back- 

 bones of these same animals ; in the brain ; in the di- 

 gestive system; in the heart and blood vessels; in 

 the muscles. 



Each of these systems is very complex, but the 



