BUTTERFLIES AND MOTHS
unveiled the glorious spectacle of the Corona, drowned at all times except during total solar eclipse in the overpowering light of the sun.
We cannot expect to find such clear-cut evidence of evolution 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 correct 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 possess 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 composed, 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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