34 EVOLUTION AND GENETICS 



species have been derived is far more probable than 

 any other view that has been proposed. 



With this unrivalled material and splendid series 

 of gradations, paleontology has constructed many 

 stages in the past history of the globe. But paleon- 

 tologists have sometimes gone beyond this descrip- 

 tive phase of the subject and have attempted to for- 

 mulate the "causes," "laws" and "principles" that 

 have led to the development of their series. It has 

 even been claimed that paleontologists are in a much 

 better position than are zoologists to discover such 

 principles, because they know both the beginning 

 and the end of the evolutionar}^ series. The reply is 

 obvious. In his sweeping and poetic vision the pale- 

 ontologist may fail completely to find out the nature 

 of the pigments that have gone into the painting of 

 his picture, and he may confuse a familiarity with 

 the different views he has enjoyed of the canvas, with 

 a knowledge of how the painting was done. 



When the modern student of variation and he- 

 redity — the geneticist — looks over the different 

 continuous" series, from which certain "laws" and 

 principles" have been deduced, he is struck by two 

 facts : that the gaps, in some cases, are enormous as 

 compared with the single changes with which he is 

 familiar, and (what is more important) that they 

 involve numerous parts in manv wavs. Since the 

 paleontologist does not know, and from the nature 

 of the case cannot know whether the differences are 



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