Page:An Essay on the Principle of Population (1798).djvu/265

 are excited to vigorous mental exertion.

As in these and similar instances, or to take a larger range, as in the great diversity of characters that have existed during some thousand years, no decided difference has been observed in the duration of human life from the operation of intellect, the mortality of man on earth seems to be as completely established, and exactly upon the same grounds, as any one, the most constant, of the laws of nature. An immediate act of power in the Creator of the Universe might, indeed, change one or all of these laws, either suddenly or gradually; but without some indications of such a change, and such indications do not exist, it is just as unphilosophical to suppose that the life of man may be prolonged beyond any assignable