Now, the earth as a planet is in process of evolution. Not many things are more certain than this. The earth has come out of fire. It has _grown_ to be what it is. Its mountains, valleys, plains, seas, shores, islands, lakes, rivers, and continents—these were not always here. They have been evolved. Not only the earth, but the entire family of spheres of which the earth is a member—the solar system—are all evolving. Mr. Spencer never did anything more profound than when he demonstrated in his ‘Law and Cause of Progress’ the universal migration of things from a condition of homogeneity toward a condition of greater and greater heterogeneity. The whole universe, or as much of it as can be examined by terrestrial instruments, has probably evolved out of the same primordial matters. The organic part of the earth has evolved, therefore, and is destined to continue to evolve, because it is a part of a whole whose habit or ambition it is to evolve. The evidence is overwhelming. The theory of organic evolution is sustained by a mass of facts not less authoritative and convincing than that which supports the Copernican theory of the worlds. Evolution is, in fact, a doctrine so apparent that it only needs to be honestly and intelligently looked into to be accepted unreservedly. It is, indeed, _more_ than a _doctrine_. It is a _known_ fact. It is a _necessary effect_ of the _conditions known to exist_ among the animals and plants of the earth. If beings _vary_ among themselves generation after generation, if only the _fittest_ of each generation _survive_ and if the survivors tend to _transmit_ to their offspring the qualities of their superiority (and the animals and plants of the earth are known to do continually all of these things), then it follows _with mathematical certainty_ that evolution is going on, and that it will continue to go on as long as these conditions continue. It is inevitable. It could not be otherwise. We would _know_ that evolution were going on among organisms where these conditions existed, even though we had never observed it. The boldest and most enthusiastic opponents of evolution have always been those with the least information about it. But the evidence is accumulating so rapidly, and is being drawn up in such unanswerable array, that, if it is not already the case, it will not be many years before it will be an intellectual reproach for anyone to discredit, or to be known to have discredited, this splendid and inspiring revelation. 1. Darwin: _Descent of Man_, 2nd edit.; London, 1874. 2. Huxley: _Man’s Place in Nature_; New York, 1883. 3. Thompson: _Outlines of Zoology_, 3rd edit.; Edinburgh, 1899. 4. Drummond: _Ascent of Man_; New York, 1894. 5. See table of geological ages, at the end of the chapter. 6. Haeckel: _The Riddle of the Universe_; New York, 1901. 7. Huxley: _On the Origin of Species_, lecture iv. X. The Genealogy of Animals.