The first forms of animal life were, in all probability, minute one-celled organisms; these left no visible fossil remains. As soon as animals developed hard parts in their bodies, such as shells and bones, we find a record of their existence as fossils. The earliest recorded forms of life were various kinds of sea-creatures, of which the modern crustacea (lobsters, etc.), snails, clams, and various shell-fishes are types. Later were developed boneless fishes, on the order of skates. After these came true fishes; then amphibia (frogs, etc.); then reptiles, birds, and, last of all, mammals, including man.
The facts are the same, whether we take the history of the successive forms as recorded as fossils in the rocks, or the living representatives that remain to tell the story in another form.
The single cell is the nucleus
The third proof, which is the story of evolution recorded in the growth and development of the individual, is yet more interesting. As life developed from simpler forms, each individual animal or plant became more complex, or carried a little further the process of growth. But the method of reproduction of new individuals remained fundamentally the same. Each individual began, like its ancestors, as a single-cell being. By the process of nutrition these single cells in each case would grow, divide, and produce various tissues and organs, but always repeating the general story of the development of the race.
Gills in the human embryo
The growth of the human embryo offers many proofs of evolution, which are wholly unexplainable upon any other theory of the origin of man, and would in themselves prove the truth of this view of man's creation were the proofs of geology entirely lacking. A single example will serve as an illustration. The human embryo at a certain period develops gill slits in the neck, the same as the embryo of a fish. This formation of unused or rudimentary organs which are afterwards outgrown, is very common throughout the animal world. In the upper jaw of a calf there are formed at a certain period incisor teeth, which never grow through the gums, but are reabsorbed and disappear as the calf develops.
I will not go further into the proofs and facts of the general theory of the evolution of animal life, but will now consider the later period of the development of man, which will show us his relation to other animals, and from which we can derive much valuable information regarding his natural physiological requirements.
MAN'S ANIMAL KINSHIP
The conception of man being descended from a monkey has been the subject of much wit and mirth.