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 mudfish, 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 fountains; 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 provoke 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 fix 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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