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on evolution as thus defined is therefore on its upward passage.

Thus what from our point of view is essential to the idea of evolution is upward passage by progressive steps (sometimes very little steps, sometimes big jumps) along definite, recognisable lines of advance, with continuity of progress from lower to higher. And of evolution in this sense there is evidence in molecules, in organisms, in minds, and in social institutions.

No doubt, when we come down to adjectival details, we shall find special features that are distinctive of each group, and some difficulty may still be felt in defining advance. I have spoken of advance to what is higher; and to illustrate what may be taken as a criterion of higher, I selected complexity. But this is not the only criterion, perhaps not the most important criterion. For, in the upper reaches of evolution, what is higher may be higher in quality. Thus one man’s treatment of a subject may be higher than that of another man not in complexity but in what we commonly speak of as “quality.” A little dinner may be higher in quality than an elaborate banquet. This distinction may be hard to define, but most people will understand what is meant.

If, with a little attentive thought, one has grasped this idea or concept of evolution as upward and progressive advance, the next thing to realise is that, throughout nature, including human nature, there is by no means always progressive advance. In every field of inquiry we find abundant evidence of that which is the very opposite of evolution and is sometimes called “degeneration” or “devolution.” I shall speak of it as dissolution. Evolution is progress, dissolution is regress. What we have now to grasp is that we find throughout nature not only upward passage from lower to higher but downward passage from higher to lower—some-