It is curious how deeply imbedded in ordinary discourse are traces of the conviction that childhood, maturity, and old age, are stages in the corporate, as they are in the individual, life. “A young and vigorous nation,” “a decrepit and moribund civilisation”--phrases like these, and scores of others containing the same implication, come as trippingly from the tongue as if they suggested no difficulty and called for no explanation. To Macaulay (unless I am pressing his famous metaphor too far) it seemed natural that ages hence a young country like New Zealand should be flourishing, but not less natural that an old country like England should have decayed. Berkeley, in a well-known stanza, tells how the drama of civilisation has slowly travelled westwards to find its loftiest development, but also its final catastrophe, in the New World. While every man who is weary, hopeless, or disillusioned talks as if he had caught these various diseases from the decadent epoch in which he was born. But why _should_ civilisations thus wear out and great communities decay? and what evidence is there that in fact they do? These questions, though I cannot give to them any conclusive answers, are of much more than a merely theoretic interest. For if current modes of speech take decadence more or less for granted, with still greater confidence do they speak of Progress as assured. Yet if both are real they can hardly be studied apart, they must evidently limit and qualify each other in actual experience, and they cannot be isolated in speculation. Though antiquity, Pagan and Christian, took a different view, it seems easier, _a priori_, to understand Progress than Decadence. Even if the former be limited, as presumably it is, by the limitation of human faculty, we should expect the ultimate boundary to be capable of indefinite approach, and we should _not_ expect that any part of the road towards it, once traversed, would have to be retraced. Even in the organic world, decay and death, familiar though they be, are phenomena that call for scientific explanation. And Weismann has definitely asked how it comes about that the higher organisms grow old and die, seeing that old age and death are not inseparable characteristics of living protoplasm, and that the simplest organisms suffer no natural decay, perishing, when they do perish, by accident, starvation, or specific disease. The answer he gives to his own question is that the death of the individual is so useful to the race, that Natural Selection has, in all but the very lowest species, exterminated the potentially immortal.