We have sketched hastily the development of the human body.  This portion of our history is marked by the successive dominance of higher and higher functions.  It is a history treating of successive eras.  There is first the period of the dominance of reproduction and digestion, purely vegetative functions, characteristics of the plant just as truly as of the animal.  This period extends from the beginning of life up to the time when the annelid was the highest living form yet developed.  But in insects and lower vertebrates another system has risen to dominance.  This is muscle.  The vertebrate no longer devotes all, or the larger part, of its income to digestion and reproduction.  If it did, it would degenerate or disappear.  The stomach and intestine are improved, but only that they may furnish more abundant nutriment for building and supporting more powerful muscles better arranged.  The history of vertebrates is a record of the struggle for supremacy between successive groups of continually greater and better applied muscular power.  Here strength and activity seem to be the goal of animal development, and the prize falls to the strongest or most agile.  The earth is peopled by huge reptiles, or mammals of enormous strength, and by birds of exceeding swiftness.  This portion of our history covers the era of muscular activity.

But these huge brutes are mostly doomed to extinction, and the bird fails of supremacy in the animal kingdom.  “The race is not to the swift, nor the battle to the strong.”  All the time another system has been slowly developing.  The complicated nervous system has required ages for its construction and arrangement.  Only in the highest mammals does the brain assert its right to supremacy.  But once established on its throne the brain reigns supreme; its right is challenged by no other organ.  The possibilities of all the other organs, as supreme rulers, have been exhausted.  Each one has been thoroughly tested, and its inadequacy proven beyond doubt by actual experiment.  These formerly supreme lower organs must serve the higher.  The age of man’s existence on the globe is, and must remain, the era of mind.  For the mind alone has an inexhaustible store of possibilities.

The development of all these systems is simultaneous.  From the very beginning all the functions have been represented, all the systems have been gradually advancing.  Hydra has a nervous system just as really as man.  It has no brain, but it has the potentiality and promise of one, and is taking the necessary steps toward its attainment.  But while the development of all is simultaneous, their culmination and supremacy is successive, first stomach and muscle, then brain and mind.  That was not first which is spiritual, but that which is natural; and afterward that which is spiritual.  But now that the mind has once become supreme, man must live and work chiefly for its higher development.  Thus alone is progress possible.