And yet the advance of the different functions is not altogether successive.  Muscle and nerve do not wait for digestion and reproduction to show signs of halting before they begin to advance.  They all advance at once.  But the progress of reproduction and digestion is most rapid at first, and it appears as if they would outrun the others.  But in the ascending series the others follow after, and soon overtake and pass by them.  And these lower functions, when out-marched, do not lag behind, but keep in touch with the others, forming the rear-guard and supply-train of the army.  And notice that each organ holds the predominance about as long as it shows the power of rapid improvement.  The length of its reign is pretty closely proportional to its capacity of development.  The digestive system reaches that limit early, the muscular system is capable of indefinitely higher complexity, as we see in our hand.  But the muscular system has nearly or quite reached its limit.  The body had seen its day of dominance before man arrived on the globe.

But where is the limit to man’s mental or moral powers?  Every upward step in knowledge, wisdom, and righteousness only opens our eyes to greater heights, before unperceived and still to be attained.  These capacities, even to our dim vision, are evidently capable of an indefinite, perhaps infinite, development.  What, as yet only partially developed, faculty remains to supersede them?  As being capable of an endless development and without a rival, may we not, must we not, consider them as ends in themselves?  They are evidently what we are here for.  Everything points to a spiritual end in animal evolution.  The line of development is from the predominantly material to the predominance of the non-material.  Not that the material is to be crowded out.  It is to reach its highest development in the service of the mind.  The body must be sustained and perfected, but it is not the end.  The goal is mind, the body is of subordinate importance.

But if this is true, we must study carefully the development of mind in the animal.  The question presses upon us; if there is a sequence of physical functions in animal development, is there not perhaps also a sequence in the development of the mental faculties?  What is the crowning faculty of the human mind and how is its fuller development to be attained?  Let us pass therefore to the question of mind in the animal kingdom.

CHAPTER V

THE HISTORY OF MENTAL DEVELOPMENT AND ITS SEQUENCE OF FUNCTIONS