Part 2

Of course the dog, the ape, the horse and man do not perfectly agree in their corresponding parts and in their natures--if they did they would belong to the same species--but their similarities are so remarkable that they have a profound meaning for the thoughtful, however meaningless they may be to the thoughtless and the prejudiced.

In embryonic development are found evidences not only of man’s close relationship with all animals but of the long, long route he and they have travelled in their common descent from the simpler forms of life. Darwin says that the whole process of reproduction, from the first act of courtship by the male to the birth and nurturing of the young, is very much the same in all mammals.

The lowest forms of animal life, the one-celled animals, are without sex, and multiply by dividing into half, each half developing into a complete cell, which in turn is subjected to the same dividing process. Many species of these lowly organisms still exist, never having developed further than the unicellular stage. All higher forms, as of fishes, reptiles, birds, mammals, begin life at this point--as a single cell. The cell, germ, or ovum of an embryo (the young of a mammal before birth) when fertilized divides, forming two cells, the two divide into four, the four into eight, and so on, until there is a colony of similar cells enmassed, and with a little rod of tissue--the beginnings of the spinal column--running through. The embryo at this stage is passing beyond the lowest grand division, the invertebrates. Entering the vertebrate division the embryo passes into the fish group. Deep grooves, gill slits, appear on the side of the neck of the embryo and six pairs of arched branches of arteries arise, just as in fishes, as if to give blood to the gills. Later all but one of these pairs disappear. The arms and legs of the child, like the legs of all other embryos, begin to develop, and continue to do so for some time, on the same plan as the fins of fishes.

Further along in its development the embryo assumes all the characteristics of the quadruped even to the tail which in the human embryo at this stage is longer than its legs. During the sixth month the entire body of the human foetus, except the palms and soles, is covered with fine, woolly hair.

Thus far the human embryo has developed in the same way, has undergone the same changes, has passed through precisely the same stages as the embryo of other animals. In its further development it leaves them all behind except those nearest man. Its tail disappears, and it now has an opposable or thumb-like great toe which with the monkey and the ape is a permanent characteristic. It is only in the latest stages of development that the human embryo presents marked differences from the embryonic ape.

Of the fact that the embryo in its development from a single fertilized cell passes through all the stages representative of the principal animal divisions, and in a progressive order from the simple to the complex and highly developed, there is no explanation but that of heredity and descent--of descent of the higher animals from the lower with heredity transmitting the records of the remote ancestral stages. Each stage, as of the fish, the quadruped, the ape, is a sign board along the route of man’s descent. The nine months’ embryonic period of each of us is an epitome of the history of the race down to the human period.

Nor do the evidences of race-history as revealed by the child cease with its birth. The babe is nearer the lower mammals than is the adult man. When it acquires the use of its limbs it begins life as a quadruped. Its blundering attempts in learning to stand erect and walk is evidence of the fact that man’s peculiar mode of locomotion is a late acquirement. Like the lower animals the babe makes known its wants by means of natural language; it later acquires artificial or spoken language in the same slow, laborious way that it was acquired by the race. At the average age of three years the child has become self-conscious; his mind has passed the mental stage of all animals below man. Psychically he has become man.

In certain periods of youth the child is a tree-climber, a cave-digger, childish sports that hark back to periods passed through hundreds of thousands of years ago in the childhood of the race. At a certain stage his emotional nature has developed to the point that he is conscious of wrong-doing. This is what the old theologians called “the age of accountability.” If there is a grain of truth in the chaff-heap of Mosaic mythology the fall of Adam indicates the point in the development of the race when conscience had dawned and feelings of remorse had begun to stir within. Man had reached the age of accountability. But prior to the “fall” there was a rise.

Rudiments or vestiges are also evidences of the descent (or ascent) of the higher forms of life from the lower. Rudiments are incomplete parts of the body which have become arrested in their development, and which are now of no use, nor would now be of use if fully developed. They are relics handed down to us by the laws of heredity from a long-past age when they were well developed and useful to our lowly ancestors. Though we outgrow primitive conditions and stages of development we can not get rid of the past, but must drag it around with us as the snail drags its shell.

All the higher animals bear within their bodies the reminders of a humble origin, some of which are: The incisor teeth of certain grass-eating animals, so rudimentary as never to cut through; the small hoof points of the cow which do not touch the ground, and the rudimentary fifth and sixth teats on the hinder part of her udder; the splint bones in the horse’s leg--vestiges of toes when he was a three-toed animal; the scanty, downy hair that covers the human body.

Certain muscles by which animals can twitch the skin are inherited by some persons who can move the scalp and the ears. The sense of smell in civilized man has become almost rudimentary. The vermiform appendix is not only useless but often injurious. It points back to the time when our ancestors were strict vegetarians--grass-eaters. In the os coccyx man carries about with him the rudimentary bones of a tail. This, with the fact that the human embryo at one stage has a tail longer than its legs, is Nature’s everlasting reminder that proud man’s remote ancestor was adorned with a tail.

In order to get as clear an idea as possible of man’s exact place in the animal scale we should note the points wherein man differs from his nearest relatives--the orang, the gorilla, the chimpanzee, the gibbon--as well as the points wherein he agrees with them. Here are the most obvious points of dissimilarity. Man walks erect, though in his first year he goes on all fours, while apes only occasionally walk, and that in a semi-erect position, their arms, longer than their legs, reaching the ground, knuckles touching. The nose of the ape is small, undeveloped; the canine teeth are very large; the mouth projects, and there is no chin. The entire body except the palms and soles is covered with hair. The brain capacity of the ape is less than half that of man.

On the other hand there are more points of similarity than of dissimilarity between man and the apes; and if the points wherein they differ be examined they will be found to be differences in degree rather than in kind. The higher apes are entirely without tails; the embryo of the ape, like the human foetus, loses its tail sometime before birth. The young ape (monkey also) is born in almost as helpless a condition as is the human babe. The female ape has two mammary glands (udders) and they are always on the chest. Adult apes have the same teeth as man--thirty-two in number, incisors, canines, premolars, molars. They have the same 200 bones, the same 500 muscles, the same organs and glands. On their toes and fingers they have flat nails, like man, instead of claws. On account of the ape’s opposable great toe they were formerly classed as four-handed; but this was an error. In all essential respects their legs terminate in feet. Like man they are bipeds, and like man they have two hands. The brain of the ape, though much smaller than man’s, as we would expect it to be, is constructed on the same general plan as his with the same main fissures and the same groups of cells. There is no “missing link” in the plan and structure of man’s brain, whatever difference there may be between his and the ape’s in capacity.

No scientist has ever been so foolish as to say that man and the apes belong to the same species. There are four species of the higher apes and one of man, though the one species of man is divided into five varieties, called “races.” Varieties differ less widely than species. Individuals within a variety also differ. Differences are no bar to unity if they are nullified and outweighed by similarities.

Finally, let us keep in mind that while man has departed from the ancestral type, developing in one direction, the apes have gone off in another and have acquired characteristics peculiarly their own. Resemblance in a babe and a young ape is far greater than in a man and an adult ape. The same is true of the young of all allied species. This divergence from birth of the adults of different species is strong evidence of a common origin.

These are only a few of the hundreds of evidences proving that man fits into the same creative scheme with the lower animals--proving that he, in common with them, has developed from still lower forms, and that, as a product of the creative forces of Nature, he is wholly subject to her laws.

CONNECTING LINKS

There is a greater unity of all life than the many divisions and sub-divisions of the analyst would seem to warrant. The dividing lines between the different classes, orders, families and species are more apparent than real, the barriers of separation not so impassable as appear at first sight.

To begin at the bottom, there is no hard and fast line drawn between living and non-living matter--or at least it is not always easy to say where the line should be drawn. Tyndall says, “The tendency of modern science is to break down the wall of partition between the organic and the inorganic, and to reduce both to the operation of forces which are the same in kind, but which are differently compounded.”

Passing on to the first grand division of life, it would seem that nothing could be plainer than the line of cleavage between vegetable and animal life. Yet there is a twilight zone between the two where each shades off toward the other, and which is inhabited by several living species of so doubtful a nature that scientists cannot agree as to which of the two great kingdoms they belong. These doubtful organisms are claimed by both the botanist and the geologist and are described in the textbooks of both. Really they do not belong to either division, but are simply organisms that have not risen in the scale of life to the diverging point of the animal and vegetable kingdoms.

Ascending the animal scale we come to the line separating the invertebrates from the vertebrates. Here, on the invertebrate side are species that have the beginnings of a backbone--an elastic smooth cord--and gill-slits, thus proving their relationship with the fishes, the lowest of the vertebrates.

The connecting link between the fish and the reptile groups is the amphibians--frogs, newts, salamanders, etc. The frog in its tadpole stage is a fish, but acquiring legs and lungs it becomes an air-breather, a land animal.

Between the reptile and the bird, and having certain characteristics of both, there are at least three extinct species, known by their fossils. One of these, archaeopteryx, had the skeleton and feathers of a bird and a reptile tail composed of twenty vertebrae. Another was a flying reptile with a bird-shaped head.

Reptiles (snakes, lizards, turtles, aligators, etc.) are cold-blooded, egg-laying animals. Birds retain the egg-laying characteristic of reptiles but are warm-blooded like the mammals. The latter differ from both birds and reptiles in producing their young alive and suckling them. Between the mammal and its ancestor, the reptile, but classed with the former is the duck-mole of Australia. It is an egg-laying, web-footed, duck-billed quadruped. After its young are hatched they are suckled in a sort of mammary pouch which is without nipples. Above the duck-mole, but so low in the mammal group that they are not really mammals are the marsupials (kangaroos, opossums, etc.). Their young are so immature at birth that they are for some time carried in a pouch by the mother.

We have now come to the last great chasm--that between man and the other mammals. As man belongs in the same group with them the chasm is not so great in the sum of physical characters as is that between the fish and the reptile groups, or between the reptiles and the mammals. In regard to man and the higher apes the dividing line, viewed from the stand-point of descent, is vertical rather than horizontal--like that between mammals and birds.

There are no species, extinct or extant, between man and the ape. It is not necessary for the proof of evolution that there should be. “Missing links” are not more required here than they are between birds and mammals which were evolved side by side from reptiles. If ten feet below the topmost bough of a tree there is another branch it is not necessary to show that there are, or have been, intermediate branches to prove that both grew from the same trunk. Missing links are required only in the line of descent.

Discoveries of the fossil remains of man are rare for many reasons. (1) Land animals rarely leave their remains in the sediment of sea and lake. (2) There is small chance of the sediment containing the fossils of recently arrived animals--more especially of man, the latest arrival--being lifted above the water level because of the slow movements of the earth’s crust. (3) Only those animal remains that are buried in localities where they will be impregnated with certain mineral salts will be preserved. (4) They must be able to resist those destructive agencies (especially erosion by water) that disintegrate the rock in which they are embedded if they are to come down to us as evidence. (5) Only a small part of the earth as yet has been searched, and nearly all the fossil discoveries have been accidental. For these reasons the geological record in respect to fossil evidences is far from complete. Yet from time to time new discoveries are filling in the gaps in the record.

Anthropologists present us with evidences of pre-historic races that were far lower than the lowest savage of today. Some of the evidences of man’s existence tens of thousands of years ago were known before Darwin set the world astir with his revolutionary discovery, and the old school geologists, like Hugh Miller, who had not been entirely weaned from scriptural literalism were sadly puzzled in regard to the evidences of these “pre-Adamites.”