In these charts we read the story of Evolution. We learn the geography of the world millions of years before the age of history; we know that this land upon which we live has not only once, but often been sunk beneath a deep sea; that during the earliest period of which there is any record unburned, there was no living thing more highly organized than a crab; not a fish nor any animal possessing the backbone that distinguishes the vertebrates to which Man belongs from the invertebrates to which belong the lowest kinds of living thing. We know that later the whole face of the world was changed, and then followed a warm period called Carboniferous, and that just before and during this Carboniferous period there slowly developed fish possessing the backbone that marks one of the great strides in animal development. But at this time we see no trace of the four-footed mammalia which immediately preceded Man.
In the marshes in which forests grew and died during the Carboniferous period, there were piled, one upon another, layers of vegetation that hardened into coal; this coal sank slowly beneath a deepening sea. In this so-called cretaceous sea were deposited, in its deepest parts, huge masses of chalk accumulated from countless shells; and upon its shores crept four-footed things resembling fish, as the seal and the sea-lion resemble them to-day, closely allied to them and clearly developed from them, as if fish stranded upon the shallows had used their fins for motion upon the banks, and out of fins made legs. And from the gigantic lizards of the cretaceous period we find in the overlying tertiary beds the infinite variety of four-legged animals which people our continents to-day.
All this knowledge, full of profound interest to the student of Man, comes from a study of the earth—Geology.
And next comes Zoölogy, telling how this amazing development of life from lower to higher forms proceeded. For centuries Man studied the living things on the earth, and added fact to fact till at last, a few years ago, Darwin, Wallace, and others demonstrated the law according to which this development takes place, the law of Evolution.
Briefly it is this:
All living things prior to the advent of Man tended to adapt themselves to their environment by the process known as the survival of the fit. Only those animals fit to survive, survived; all the rest perished. When there was a change of environment, as, for example, of climate, only those individuals survived that were capable of adapting themselves to this change.
The process by which animals adapt themselves to changes of environment is as follows:
There is in every new generation of animals an infinite variety; some differ enough from the rest to be called "sports." These differences are transmitted to future generations by heredity. Men have used these differences to create types of animals suited to their purpose. Thus by putting stallions built for speed to mares similarly built, Man has produced the race-horse. On the contrary, by putting stallions built for drawing loads to mares similarly built, Man has produced the cart-horse.
Before the advent of man this selection of types was made by the environment or by Nature, as the environment used to be called. Hence the expression, natural selection, is used to describe the process by which Nature or environment selects certain types for survival at the expense of the rest; the process by which animals that live in the desert gradually adapt themselves to endure great heat; and those that live near the Poles gradually adapt themselves to endure great cold.
The environment or Nature uses in this process of selection a very cruel but effectual device: A great many more living things are born into the world than the world can support. In the lower forms of life Nature is wastefully fertile; thousands of herrings' eggs are laid for one herring that grows to maturity. This amazing fertility of Nature results in a struggle for life which condemns the enormous majority of living things born into the world to an early death, but has the singular advantage of allowing only the types most fitted to the environment to survive. And this process of natural selection acting in an environment favorable to development from a lower to a higher type has gradually caused the lowest forms of life, which consist of a mere sac of so-called protoplasm, to develop organs especially adapted to accomplish specific things: a mouth to take in food; a stomach to digest it; bowels to assimilate it; a system of circulation—arms and legs; a nervous system; a brain; ears; a nose; eyes; until at last, in the order of creation as demonstrated in the great Book of the Rocks, and as confirmed by zoölogy and other sciences, Man has evolved out of the original protoplasmic sac.