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formation. The pedigrees of the horse, camel and elephant are fairly complete. One of the first criticisms of the theory of evolution concerned the so-called "missing links" which should be forms intermediate between various types of life. True enough there are links missing and missing links also. The chance of survival of representatives of any type of life over vast ages is small enough, and the chance that they may be discovered in fossil form by a man informed enough to understand is perhaps even less. Nevertheless, connecting links are known, some of them among living animals. The Dinophilus lies between the flatworms and the annelids (such as earthworms). There are primitive centipedes connecting worms and centipedes. The lung fishes may live out of water and breathe air. The monotremes of Australia remind us of reptiles as well as birds. Attention was called earlier in the chapter to the difficulties of classification due to the presence of intermediate forms between the species. Even the oldest fossil remains of the human family differ widely from present skeletons.

In the history written in the rocks a history not written by man, inspired or uninspired, but written in a language man can read-long ages pass ere warm-blooded mammals are found. As earlier noted, Asia appears to have been their distribution center. The primates first appear in the lower Eocene deposits both of Europe and North America. These rocks in Wyoming and New Mexico contain many remains. They disappear at the close of the Eocene, to reappear and survive in South America. The history of Europe is similar except that Europe is invaded by the Barbary ape of Africa in the Miocene which disappears at the close of the Pliocene save in Gibraltar where it still survives.

Morphology or Comparative Anatomy

The architect of organic life has used certain structural plans over and over. All fish have a similar structure in spite of wide specific differences. The same is true of mammals whether they walk on one toe like the horse, or flat-footed, like man. Common observation tells us that the greater the resemblance in details the closer the actual relationship. Identical twins are more nearly alike than ordinary brothers, cousins vary still more. The Yankee and the Eskimo are far apart yet it is evident that they are cast in the same pattern. From the standpoint of structure there is no question as to the position of man. Bone for bone and muscle for muscle he resembles the apes, and the finger prints of the chimpanzee cannot be distinguished from human prints. These primates are classified as follows:

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I. Lemurs: really connecting links between insectivora and primates.

II. Anthropoids: Broad-nosed monkeys, tails often prehensile; spider monkeys, marmosets.

III. Narrow-nosed Apes:

I. Tailed apes: Chests narrow. No vermiform ap

pendix. Baboons.

2. Tailless apes: Broad breastbones. Opposable thumbs. Gibbon, orang-utan, gorilla, chim

3. Man.

panzee.

Of the great apes classified next to man, the gibbon has the longest arms and is a great tree-traveler. It is found in southeast Asia and adjacent islands. It stands erect, using its long arms to balance it as it walks. The orang-utan of Sumatra and Borneo is a heavy, sluggish, ground-dweller. On all fours it can scarcely bend back its head far enough to look straight ahead. The gorilla of Africa is the largest of all, weighing up to 360 pounds with a height of 5 feet 7 inches. Its life is almost wholly terrestrial. The chimpanzee of Africa, often 5 feet tall, has short arms, and stands next to the gibbon in time spent in the trees. Like the other apes its skull is short and that of the female most closely resembles the human skull.

Aside from the absence of a hairy covering man differs from the apes chiefly in his brain development. He stands more erect. The brains of the apes are well developed, averaging between 400 and 500 c.c. though chimpanzees with brains of only 200 c.c. have been found while the gorilla is known to have 610 c.c. at times. To meet human demands, brains of at least 960 c.c. are required.

Serology

Blood tests. Not long ago it was discovered that if human blood were injected into rabbits an anti-human serum would develop which would produce a white precipitate if brought into contact with human blood. This has proved to be a most efficient means of testing relationships. If this serum is put in contact with the blood of the apes a precipitate is formed, less quickly and in smaller amount. The blood of monkeys reacts still more slowly and to a smaller degree but the reaction may be traced even in the lemurs. No other blood gives the reaction.

Geographical Distribution

Similar regions in different parts of the earth have varying faunas and floras even though the same types of life be present. The elephants of Asia and Africa are not identical. The monkeys of Africa and South America are different. The desert regions of North America offer many local races of birds with color schemes peculiar to the area, such as the horned larks. Unless we assume special creations for the different continents we must assume some common ancestors and different variations. This is seen most clearly in isolated islands, a fact which early impressed Darwin when he visited the Galapagos. It is claimed that on Saint Helena, a thousand miles from Africa, there are: 129 species of beetles (all but one unique), belonging to 29 genera, of which 25 are unique; 20 species of land snails, of which 17 are unique; 26 species of ferns, of which 17 belong to unique genera.

Embryology

The science of development. Every one knows that an individual starts as a single cell and develops to mature form. The adult could not live under the conditions of its early existence. The growth of the organs of the body, such as the heart, curiously approximates the forms found in lower organisms. Hence arises the "recapitulation theory" which suggests that the individual recapitulates the history of the race. Often these early traits survive as vestigial organs of no present value or use. The horse shows its useless toes. At one stage the human embryo has a fish-like heart, brain, muscles, alimentary tract and even gill slits in the side of the neck. Later on it closely resembles the embryo of the rabbit or cat. Still later it is like the embryo of the ape and is covered with a coat of hair, which is shed, ordinarily, before birth. After birth the child holds its legs just as do the apes, and the spinal column is a single curve, as that of the ape, while in the adult man it has a double curve. The hairs of the human body have the same slant as those on the ape. The human infant for a few weeks after birth has a marked power of supporting itself by hanging on a stick with its hands.

Save in rare cases the human adult is tailless and the four or five lower vertebræ are fused but in fetal life the tail develops much as in other mammals and at one stage is longer than the legs. It is claimed that man has some 184 vestigial structures among which are the muscles which move the ears and the skin, the traces of an extra eyelid, the pineal gland, and, best known of all, the vermiform appendix, a doubtful honor which man shares with the simians. All animals have such vestigial organs and no explanation of their presence can be given save in terms of the evolutionary

theory.

Genetics

The science of breeding. In as much as this is the center of interest in biology to-day its discussion cannot be limited to a paragraph and must form the subject of the next chapter. Suffice it to say that all the evidence it offers supports the idea of evolution.

Finally it should be noted that the dependence of the higher upon the lower organisms gives a certain support to a theory of evolution. Obviously, lower forms may live as parasites on higher animals and might conceivably arise later in some cases but the development of the higher forms without the prior presence of the lower to modify the environment and make the higher forms possible is simply unthinkable.

THE LADDER OF LIFE

At the bottom of the ladder of animal life we find the single-celled forms, such as the ameba common in vinegar, a membrane filled with liquid and enclosing a nucleus. In the ordinary sense of the term there is no specialization of organs.

Higher than the amœba stand the animals made up of many cells arranged in two layers. The hydra is a cylinder closed at one end where it is fastened to the rocks. At the open end of the cylinder are tentacles which by their motion cause currents of water to enter, thus introducing particles of food. The outer cells are protective, the inner layer digests the food.

Next in the scale are the worms in which we find a series of cylinders fastened together. These segments are much alike in structure and function, but with increasing specialization. This form characterizes the great mass of invertebrates. Crabs and lobsters as well as beetles and butterflies are built

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