There is, however, another set of relations which have been hitherto very little studied--those between the organic and the inorganic worlds in their broader aspects. These are now found to be very much more complex and more remarkable than is usually supposed, and they also have an important bearing upon the great problem of the origin and destiny of man. This is a subject which opens up a variety of considerations of extreme interest, showing that the exact adaptations of our earth--and presumably of any other planets--to enable it to sustain organic life, from its first appearance and through its long course of development, is as varied and complex and as much beyond the possibilities of chance coincidences as are any of the individual adaptations of animals and plants to their immediate environment. Most of these latter adaptations have been made known to us by Darwin and his followers, and they have excited the admiration and astonishment of all lovers of Nature. When the antecedent and grander relations of planet to life are studied with equal care, these also will, I believe, excite deeper admiration, still more profound astonishment, because any secondary laws that could have brought them about are less easy to discover, or even to imagine. [Sidenote: Essential Conditions of Life] Before we can form any adequate idea of the nature of a world which shall be able to support and develop organic life, we must consider what are the special conditions that alone render such life possible. We, of course, refer to the whole of the organic world, from the lowest to the highest, not to the few exceptional cases in which life may be possible under conditions that would be fatal to the higher as well as to most of the lower forms. [Sidenote: The Miracle of Human Life]