forms. It is constantly in action, from the germ up to maturity. There is as fierce a battle between germs as between grown animals as to which shall survive. The ill-adapted embryo perishes; the well adapted lives. Of the multitudes of young, only those survive which are best fitted to obtain food and escape peril. There is thus a succession of conditions to which the growing form must be successively adapted, and each mature form is the sole survivor of a myriad of germs which started together in the race of life. It has been sharply selected out as the best adapted.
The law of adaptation thus works vigorously throughout all embryonic development. It works as decisively on mature forms. They must be closely adapted to certain conditions of nature; but the possible variation in conditions is almost boundless. Not only in time have there been constant changes in natural conditions, and not only do they now widely vary in different localities, but even in the same locality a great variety of differing conditions simultaneously exist.
As the simple atoms of the chemical elements unite to form complex compounds, so do simple conditions unite into complex. Numerous sets of minor conditions exist together, from whose combination are formed less numerous major conditions, and from these again a single highest condition which includes all below its level. Thus each locality may possess its many sets of simpler forms, and sets of superior forms narrowing in number as they become adapted to a wider environment, until a highest or most complex form is reached, which is in physical harmony with the totality of existing conditions.
And the question of superiority and inferiority between animals is simply a question of the greater or lesser complexity of the conditions to which they are fitted, the broader or narrower field of adaptation which they occupy.
But, in this quick pressing of new forms into every nook and cranny of nature, there are certain general principles which have a controlling influence over the resulting changes in form. One consideration must always be taken into account, that of the character of organic material—of protoplasm—and the forms it naturally tends to assume. And a second consideration is that of the main end of animal life—the absorption of aliment. From this latter it follows that the basic type of animal form is the stomach; and in viewing the field of animal development we behold only a series of stomachs, provided with various food-taking and danger-escaping appendages.
Evolution, then, means the gaining of superior powers of providing for the needs of this voracious core of all animals, the stomach; and of superior powers of escaping the voraciousness of other armed and perambulatory stomachs.
The aliment on which organisms subsist is of three kinds—mineral, vegetable, and animal. The pursuit of these yields two distinct classes of organisms. Mineral food needs to undergo a high degree of chemi-