70 THE NEXT GENERATION 



i . Structural evidence derived from the form and general 

 make-up of animals. It is often found in rudimentary bones 

 and organs — leg bones of the whale, for example, toe bones 

 of the horse, etc. Darwin himself was thinking of structural 

 evidence when he wrote, "What can be more curious than that 

 the hand of man, formed for grasping, the leg of the horse, 

 the paddle of the porcupine, and the wing of the bat, should 

 all be constructed on the same pattern, and should include 

 the same bones in the same relative position." 



2. Embryological evidence. This includes such rudiments 

 as are found in the embryo alone — gill-slits, for example. 

 Without this important embryological evidence we should 

 not so much as suspect that in early ages all vertebrates 

 lived in the water. 



3. Geological evidence gathered from fossil bones etc. 

 This gives us the pedigree of the horse back to his five-toed 

 ancestors, and shows what kind of creatures lived on the earth 

 before man himself arrived. 



4. Geographical evidence. This shows that creatures which 

 are most alike are found nearest together. 



5. Experimental evidence. Man gets this for himself 

 when he chooses different. varieties and breeds new species 

 of animals. 



Taken all together, these five kinds of evidence prove that 

 at some time in the past all vertebrates were very much more 

 alike than their descendants are to-day ; and,' as we have seen, 

 these present differences are the result of the combined action 

 of environment and heredity 1 . The two, working together, 

 have caused such specialization along different lines that we 

 now have many different types of vertebrates. Some of these 



1 " By heredity we mean organic resemblance based on descent." — 

 Castle. 



