Use them we must. Man is placed in such a position that he must study what passes round him. Man learns by experience. Instincts are but slightly progressive. Unless brought into contact with man, the animals learn little--perhaps nothing. I do not doubt but that those huge monsters, whose remains we behold in geological museums, were the most dull and stupid creatures possible. I think this simply because I suppose that man did not then exist, and, therefore, that these monsters had nothing to waken them up out of their sluggish torpor. But scientific men[26] tell me that existing mammals actually have larger brains than their ancient tertiary prototypes of the same order. Let man enter the stage, and the instincts of animals are quickened. Nature did not create man without taking care to guard the inferior animals from his destructive powers. But man in himself, essentially, is at once progressive and retrogressive. Bound up with him is an infinite possibility of advance and decay. He is never stationary. Both individuals and communities are perpetually either ascending or descending in the scale, morally and intellectually. But this law of nature obliges man to perpetual mental effort under the usual penalty of degradation. We have not merely to advance, to win new ground. If this were all, at length we should have nothing to do. We have to win back lost ground. Our gains are, I hope, greater than our losses; but the progress of no community will ever be fast enough, continued enough, and assured enough, to justify the members of it in living in a fool's paradise. This, then, was our second point. The first was, that nature has provided us with a proper field for the exercise of our mental faculties; the second, that she imposes upon us the necessity of using them.