PROBLEM 



tJ What Puzzling Facts May Be Explained 

 by Our Theory of the Origin of New 

 Organisms? 



Resemblances in structure. It has been 

 known for a long time that animals as 

 different in their outward appearance and 

 in their way of life as birds, cats, codfish, 

 and snakes, for example, have similar skel- 

 etons. You will recall that each of these 

 animals has a backbone composed of 

 many short bones called vertebrae. Each 

 vertebra has a large hole through it; the 

 spinal cord passes through this hole. The 

 skulls of all these animals are much alike; 

 many of the bones that make up the skull 

 are similar in structure and position. The 

 bones attached to the backbone, such as 

 the ribs, the hip girdles, and the append- 

 ages (legs and arms) are strikingly alike. 

 See the photographs of skeletons in Fig- 

 ure 499. When you examine the front ap- 

 pendage of two mammals that are as dif- 

 ferent as man and the whale you will be 

 struck by the similarity in bony struc- 

 ture. See Figure 498. In fact the arm of 

 the monkey, the wing of the bat, the 

 front leg of the cat, and the flipper of the 

 seal are all similar in bony structure, yet 

 these animals live in different environ- 

 ments and use their appendages in very 

 different ways. See Figure 500, page 548. 

 Animals as different as fish, frogs, tur- 

 tles, birds, and cats are similar in other 

 ways. In Figure 257, page 273, are draw- 

 ings of the brains of several vertebrates. 

 Note the similarities and differences. Al- 



most all the organs of one vertebrate re- 

 semble those of the other vertebrates even 

 though the animals are different in out- 

 ward appearance and in their modes of 

 living. You will find it interesting to sum- 

 marize this paragraph by doing Exer- 

 cise I. 



Arm of man 



Fig. 498 Although the whale and man have 

 different habits of life and are different in ap- 

 pearance, the bones of the whale's flipper are 

 much like the bones of a man's arm. What re- 

 semblances do you find? 



