One of the latest authorities[2] on anthropology has told us that 'to develop soul is progress', and he has followed the clue through the meagre relics of Palaeolithic and Neolithic man. So does the last science of the nineteenth century throw light on the dim recesses of the past. For unquestionably psychology is the characteristic science added to the hierarchy in our period; it has crowned biology and is exercising a profound influence on philosophy, literature, and even politics. If Aristotle was its founder, if it was Descartes who first showed its profound connexion with philosophy, it is to workers in our own day that we must look for those methods of accurate observation, comparison, and the study of causes without which it could not advance farther. And modern psychology has advanced far enough to see that we must include in its purview the 'soul' of a minnow as well as of a man. Descartes had stopped too short, for to him animal life, as distinct from human, showed only the movements of automata. But now, just as the biologist conceives man as part of one infinite order of living things, so the psychologist believes that the facts of his consciousness, the crown of life, must find their place somewhere related to the simplest movements of the amoeba. Hence the whole of animate evolution, and not only that part of which Dr. Marett spoke, may be thought of as the growth of soul. But, the objector will inquire, does this imply the enlargement of every individual or even of the average or the typical personality? And if not, what becomes of a 'growth of the soul'? To this we must admit the impossibility of any complete, or even approximate, answer with our present knowledge. We can only note one or two points of certainty or of confident belief. The first, that there have been individual men, an Aristotle or a Shakespeare, in the past, with whom later ages never have, and perhaps never may, compare. The second, that there are good grounds for thinking that the average man has improved in goodness and in knowledge since we first knew him dimly in the dawn of history. But more important and more certain is the fact that the collective soul of man has grown, and all the extensions of knowledge and of power of which our volume speaks bear witness to it. They are essentially social in origin and outlook, and rest on a foundation of common thought immeasurably wider than any in the more distant past.