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Chapter 8 



Experimental Transformation of Species 



THE historian is able to tell us with an adequate degree 

 of accuracy something of the succession of rulers of 

 some ancient nation. Perhaps a full series of coins 

 or of postage stamps will tell us such a consistent and com- 

 plete story. Quite analogous is the significance of a series 

 of fossil plants or animals. The chalk cliffs of England tell 

 us among other things that with the passing of time there 

 appeared a succession of sea urchins having distinct forms. 

 There can be no question about the facts: A preceded B, 

 B preceded C, and so on through the ages. In addition to the 

 difficulties inherent in the historical studies, organic evolu- 

 tion presents the problem of genetic relationships. It is not 

 enough to know that Augustus followed Julius or that 

 Edward followed Victoria. We want to know what rela- 

 tionship there was between one ruler and the next, or be- 

 tween one dynasty and the next. 



In historical studies, such information is generally part 

 and parcel of the record that reveals the succession. In the 

 study of the history of plant and animal forms this is not 

 the case. The succession is at best a presumption of descent 

 and is indeed accepted as such where the resemblances, or 

 rather the differences, do not raise any doubts. But the 

 whole crux of the question lies in the very modifications that 

 do raise such doubts. It is one thing to say that ferns fol- 

 lowed mosses and liverworts, but a very different thing to 

 say that ferns descended frovi mosses and liverworts. It is 

 easy enough to show that deers with large and branched 

 horns succeeded deers with similar and smaller horns, and that 

 these succeeded deers with no horns at all (Fig. 57). It is 



