WHY WE MUST BE EVOLUTIONISTS 



the evolutionary wind has blown. In a great many ways 

 the individual animal climbs up its own genealogical tree, 

 but we must be careful not to think that an embryo mammal 

 is at an early stage of its development like a little fish, as 

 some writers have carelessly said. Each living creature, 

 from the very first stage of its development, is itself and no 

 other; and though the tadpole of a frog has for some weeks 

 certain features like that of a fish, especially a larval mud- 

 fish, it is an amphibian from first to last. The embryo is the 

 memory of a fish or of a reptile-like ancestor. There is no 

 doubt that the hand of the past is upon the present, living 

 and working; and this is evolution. 



Many living creatures today are like ever-changing foun- 

 tains; they are continually giving rise to something new. 

 The beautiful evening primrose (Oenothera) and the 

 American fruit-fly {Drosophila) are notable examples of 

 changeful types; they are always giving birth to novelties 

 or new forms, technically called "variations" or "mutations"; 

 but the fact of variability is widespread. 



In some forms the breeder or the cultivator is able to pro- 

 voke great changes, for instance, by altering surroundings 

 and food; but he usually has to wait for what the natural 

 fountain of change supplies. This has been our experience 

 with the domesticated animals and cultivated plants that 

 interested Darwin so much. All the domestic pigeons have 

 been derived, under man's care, from the blue rock dove; 

 and there is strong evidence that the multitudinous breeds 

 of poultry are all descended from the Indian jungle-fowl. 

 What Darwin said was this: If man can kii and foster this 

 and that novelty and make it the basis of a true-breeding 

 race, and all in a comparatively short time, what may Nature 

 not have accomplished in an unthinkably long time? And 

 when it was objected: But what is there in Nature corre- 



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