It is only when we have such a clear
understanding that we can profitably pursue the further inquiries into the
evidence of evolution. Our first real task, therefore, is an inquiry into
certain fundamental questions about life and living things, upon which we
shall build as we proceed.
* * * * *
All living things possess three general properties which seem to be
unique; these are a peculiar chemical constitution, the power of repairing
themselves as their tissues wear out, and the ability to grow and
multiply. The third property is so familiar that we fail to see how
sharply it distinguishes the creatures of the organic world. To realize
this we have only to imagine how strange it would seem if locomotives and
steamships detached small portions of themselves which could grow into the
full forms of the parent mechanisms. Equally distinctive is the marvelous
natural power which enables an animal to re-build its tissues as they are
continually used up in the processes of living; for no man-made,
self-sustaining mechanism has ever been perfected. The property of chemical
composition is believed by science to be the basis of the second and the
third; but this matter of chemical constitution must take its proper place
in the series of structural characters, which we shall discuss further on
as we develop the conception of organic mechanism.
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