The Fifth Kingdom refers to a transhuman state of higher Consciousness that is achieved via a process of "intentional evolution" This Fifth Kingdom is presumably achieved only when one's "animal nature" is thoroughly subdued via an uncompromising suppression of the emotional, passion, irrational, and animalistic side of the Physical Unit. As Lomas writes:
Darwin tells us that in Nature we find our kingdoms of consciousness, three prehuman and one human. It is unthinkable that evolution should stop and come to a cul-de-sac in the human, so we can visualize a fifth kingdom. This is the kingdom of Initiates. At present we are animals with divine possibilities, and the savage legacy of our primeval origins must be driven below the threshold of our consciousness before those possibilities can come into play.
In Christianity the Fifth Kingdom is revealed in one of Nebuchadnezzar's prophetic dreams. Interpreting the king's dream, Daniel says that the Fifth Kingdom is a Kingdom created by God (i.e. created by high Consciousness) that "crushes" the previous four Kingdoms (gold, clay, bronze, and iron) and endures forever on Earth.
In the time of those kings, the God of heaven will set up a kingdom that will never be destroyed, nor will it be left to another people. It will crush all those kingdoms and bring them to an end, but it will itself endure forever. This is the meaning of the vision of the rock cut out of a mountain, but not by human hands—a rock that broke the iron, the bronze, the clay, the silver and the gold to pieces. Daniel 2:44-5.