The wheel of evolution is such that the consciousness gradually evolves through rock, tree, animal, to man. When it reaches man it cannot manifest further toward the surface, because through this journey all its force is spent. Man is the most active being, he has to do with most things. A rock has very little activity; it lasts long. A tree has a little more activity, and its life is not so long as that of the rock. There are many animals which live much longer than man. Man has the most activity, and in him the consciousness reaches the highest point of manifestation.