This truth will be most clearly seen if we reduce it to its purely abstract form, thus:--Suppose a quite homogeneous species, placed in quite homogeneous conditions; and suppose the constitutions of all its members in complete concord with their absolutely-uniform and constant conditions; what must happen? The species, individually and collectively, is in a state of perfect moving equilibrium. All disturbing forces have been eliminated. There remains no force which can, in any way, change the state of this moving equilibrium; either in the species as a whole or in its members. But we have seen (_First Principles_, § 173) that a moving equilibrium is but a transition towards complete equilibration, or death. The absence of differential or un-equilibrated forces among the members of a species, is the absence of all forces which can cause changes in the conditions of its members--is the absence of all forces which can initiate new organisms. To say, as above, that complete molecular homogeneity existing among the members of a species, must render impossible that mutual molecular disturbance which constitutes fertilization, is but another way of saying that the actions and re-actions of each organism, being in perfect balance with the actions and re-actions of the environment upon it, there remains in each organism no force by which it differs from any other--no force which any other does not meet with an equal force--no force which can set up a new evolution among the units of any other.