One ripple overwhelms or effaces another and a curling breaker leaps up from behind them and sprays the shore far in advance of the main body of invading waters.
Evolution reaches out similarly, now advancing, now retreating in unconsidered wavelets, always gaining, always effacing the old with the new, and inevitably dominating the entire situation at last.
The ebb tide affords a symbol of Involution which lays bare the way for another era of flood, so that every drop in the ocean taking its turn may ultimately rise to its highest mark of attainment.
Involution is usually described as a sort of compensatory process, coördinate with evolution, though not co-incident with it. It is regarded as a return swing of the pendulum of evolution and is sometimes crudely illustrated by comparing the two to the corresponding halves of a circle matched together so as to form a completed ring or hoop. But this symbol though impressive is misleading, for involution matched with evolution can not bring about any condition of finality.
If that were possible evolution would end in extinction—and extinction is unthinkable.
The pairing of the two processes does not complete a circle. One does not match the other and neither can undo the other's work. If there could be a counter-action between them, each would efface the results of the other, as soon as its hour of activity began.
For illustration one may consider the progress of a bud which in due course of evolution unfolds into a rose fully expanded. That rose does not refold and become again a bud.
And if it did, that would not be involution. It would be only retrogression. Involution does not follow upon the heels of evolution to match its movements with opposing influences. It doesn't interfere at all. If it did there would be no unfolding of Nature's plans, for all her efforts would cancel each other.
Doubtless the two processes work towards the same result in obedience to a systematic divine idea and purpose, and, not leading up to any finality, they form a cycle rather than a circle and may be best pictured as a continuous spiral and not as a completed hoop.
It would then be seen that involution and evolution succeed each other in rotation as the night follows day and the day gives place to night. Each period of one followed by the other forms a coil in the spiral. And the spiral is continuous, being itself only one coil in a greater cycle which, in its turn, forms part of a still more extensive series of coils. And thus they go on to infinity, for they can never reach a limit. And the processes of our involution and evolution are only coils of a cycle that has gone on forever and they will continue to form new coils to all eternity.