THE PROGRESSION OF LIFE ON EARTH
By Sir Arthur Smith Woodward
Past-President of the Linnaean and Geological Societies
If we compare the various groups of animals of the present day we shall find that they can be arranged in a series that gradually leads from the simplest to the most complicated—from the lowest to the highest. The lowest forms are minute specks of jelly-like substance, in which feeding does little beyond helping multiplication. Next higher we find animals of more elaborate structure, in which feeding is improved by the presence of small muscles that make grasping easier. Muscles next form a greater proportion of the body and are used for moving about; and in forms still higher we find nerves to control them. Muscles for locomotion work better by being attached to a skeleton, and in the early forms of life this is altogether an outside shell like that of a cockle, a lobster, or a fly. The nerves next gradually become more elaborate and usually tend to be thickest in the head.
New possibilities arise in still higher forms, in which the muscles are fixed to an internal skeleton, around a backbone, and the front end of the nervous system becomes a brain. Next, the blood no longer remains of the same temperature as the surrounding water or air, but is warmed by an improvement in the heart. The brain grows in size and complexity, fostering activity and leading to the development of higher intelligence. Finally, there comes Man, mastering the world by his greatly developed brain.
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