The mutation factor in evolution : with particular reference to Oenothera / by R. Ruggles Gates.

  • Reginald Ruggles Gates
Date:
1915
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Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: The mutation factor in evolution : with particular reference to Oenothera / by R. Ruggles Gates. Source: Wellcome Collection.

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    in the infinitely complex result we call evolution. An understanding of the multifarious diversity of the earth's present flora and fauna requires also the recognition of the effects, e.g., of geographical and physiological isolation, and no doubt also many features which have not yet been recognised in the activities of organisms. By evolutionary factors we therefore mean activities, of whatever nature, leading to specific diversity. Though mutations are but one of the diversifying activities of organisms, they have the distinct advantage of being, not linear, but in many directions. Just as an alpine climber dangling over a chasm may, by changing his hold, swing himself on to a shelf from which he can make a fresh start in some other direction, so we may think of the organism trying many unconscious experiments in its offspring, some of which are hurled by the gravita tional effect of natural selection into the abyss of extinc tion, while others with a more fortunate turn rest on a ledge of safety whence new essays of variability begin. The desire of the climber is to get to the top, but we cannot attribute any such fixed purpose to the organism, and it seems more reasonable to ascribe the increase in com plexity associated with much of evolution to the chemical and structural complexity of the protoplasm and espe cially to its unique property of irritability. On the other hand, only a tithe of the evolution we know has been progressive. Much of it has been retro gressive, and still more divergent. The causes of diver gences and of progress are the things to be explained. Aside from the infinitely labyrinthine by-paths of di gression and retrogression, the main high road of evolu tion, if there is one, can only be conjectured in a simplified way by projecting backwards to their hypothetical meeting points the main axes of the various phyla of organisms. When this is done, those meeting points are found to be for the most part lost
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