BUTTERFLIES AND MOTHS 



unveiled the glorious spectacle of the Corona, drowned at 

 all times except during total solar eclipse in the overpower- 

 ing light of the sun. 



We cannot expect to find such clear-cut evidence of evolu- 

 tion in the story of life on the earth, but we have abundant 

 opportunities of applying a test that is in principle the same 

 as that which justifies our belief in the astronomical theory. 



If the theory of the movements of the solar system is cor- 

 rect an eclipse will take place at such a time and place; if the 

 theory of evolution is true then certain organs or parts should 

 be found in the ancestors of animals that do not now pos- 

 sess them or perhaps still exist in the early stages of animals 

 of to-day. We search in the rocks, we find and dissect the 

 early stages, and there the missing parts are revealed. The 

 prediction founded on the theory of evolution is verified. 



In order to convince others it is necessary to be convinced 

 oneself, and nothing is so convincing as personal experience. 

 Therefore I will tell of a prediction founded on evolution 

 and its verification nearly forty years ago. 



Few people, I suppose, realize that their teeth are among 

 the most ancient of the parts that make up the human body. 

 They are, for example, older than the hair, which was 

 derived from the horny scales of ancestors much nearer to 

 our own times than those which gave us our teeth. Teeth 

 have come by direct descent from a remote ancestor that 

 was covered with scales like a shark — scales which in this 

 ancestor, as in the shark, passed over the lips into the mouth 

 and, without any essential modification of structure, were 

 used as teeth. The scales and the teeth of sharks are com- 

 posed, like our own teeth, of hard dentine, developed from 

 cells below the epidermis, or surface skin, covered with the 

 much harder enamel, developed, at any rate mainly, from 

 the epidermis itself. Scales of this kind and teeth have the 



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