Part 5

An irrefutable proof that such single-celled primæval animals like the amoeba really existed as the direct ancestors of man, is furnished, according to the fundamental law of biogeny, by the fact that the human egg is nothing more than a simple cell.

The next step taken in advance is the division of the cell in two;--there arise from the single germinal spot two new kernel specks, and then, in like manner, out of the germinal vesicle two new cell-kernels. The same process of cell-division now repeats itself several times in succession, and the products of the division form a perfect union. This organism may be called a community of amoebæ (synamoebæ).

From the community of amoeba morula, now arose ciliated larvæ. The cells lying on the surface extended hair-like processes or fringes of hair, which, by striking against the water, kept the whole body rotating--the lanceolate animals or amphioxus were thus first produced. Here we find from the synamoebæ which crept about slowly at the bottom of the Laurentian primeval ocean by means of movements like those of an amoeba, that the newly-formed planæa by the vibrating movements of the cilia, the entire multicellular body acquired a more rapid and stronger motion, and passed over from the creeping to the swimming mode of locomotion. The planæa consisted, then, of two kinds of cells--inner ones like the amoebæ, and external "ciliated cells." The ancestors of man, which possessed the form value of the ciliated larva, is, of course, extinct at the present day.

Out of the planula, then, develops an exceedingly important animal form--the gastrula (that is, larva with a stomach or intestine), which resembles the planula, but differs essentially in the fact that it encloses a cavity which opens to the outside by a mouth. The wall of the progaster (primary stomach) consists of two layers of cells: an outer layer of smaller ciliated cells (outer skin or ectoderm), and of an inner layer of large non-ciliated cells (inner skin or entoderm). This exceedingly important larval form, the "gastrula," makes its appearance in the ontogenesis of all tribes of animals. These gastræada must have existed during the older primordial period, and they must have also included the ancestors of man. A certain proof of this is furnished by the amphioxus, which, in spite of its blood relationship to man, still passes through the stage of the gastrula with a simple intestine and a double intestinal wall. By motion of the cilia or fringes of the skin-layer, the gastræa swam freely about in the Laurentian ocean.

The development of the gastræa now deviated in two directions--one branch of gastræads gave up free locomotion, adhered to the bottom of the sea, and thus, by adopting an adhesive mode of life, gave rise to the proascus, the common primary form of the animal plants (zoophyta). The other branch was originated by the formation of a middle germ-layer or muscular layer, and also by the further differentiation of the internal parts into various organs; more especially, the first formation of a nervous system, the simplest organs of sense, the simplest organs for secretion (kidneys), and generation (sexual organs)--this branch is the prothelmis, the common primary worms (vermes). Like the turbellaria of the present day, the whole surface of their body was covered with cilia, and they possessed a simple body of an oval shape, entirely without appendages. These acoelomatous worms did not as yet possess a true body cavity (coelom) nor blood. No member of the next higher animals are in existence, neither are there any fossil remains, owing to the soft nature of their body. They are therefore called soft worms, or scoleceda. They developed out of the turbellaria of the sixth stage by forming a true body cavity (a coelom) and blood in their interior. The nearest still living coelomati is probably the acorn worms (balanoglossus). The form value of this stage must, moreover, have been represented by several different intermediate stages.

Out of the four different groups of the worm tribe, the four higher tribes of the animal kingdom were developed--the star-fishes (echinoderma) and insects (arthropoda) on the one hand, and the molluscs (mollusca) and vertebrated animals (vertebrata) on the other. Out of certain coelomati, the most ancient skull-less vertebrata were directly developed. Among the coelomati of the present day, the ascidians are the nearest relatives of this exceedingly remarkable worm, which connect the widely differing classes of invertebrate and vertebrate animals. To these animals have been given the name of sack-worms (himatega). They originated out of the worms of the seventh stage by the formation of a dorsal nerve marrow (medulla tube), and by the formation of the spinal rod (chorda dorsalis) which lies below it. It is just the position of this central spinal rod or axial skeleton, between the dorsal marrow on the dorsal side and the intestinal canal on the ventral side, which is most characteristic of all vertebrate animals, including man, but also of the larvæ of the ascidia.

We now come to the second half of the series of human ancestors. The skull-less animal lancelet, which is still living, affords a faint idea of the members of this group (acrania). Since this little animal, in its earliest embryonic state, entirely agrees with the ascidia, and in its further development shows itself to be a true vertebrate animal, it forms a direct transition from the vertebrata to the invertebrata.

At this stage, most probably, the separation of the two sexes began. The simpler and most ancient form of sexual propagation is through double-sexed individuals (hermaphroditismus). It occurs in the great majority of plants, but only in a minority of animals; for example, in the garden-snails, leeches, earth-worms and many other worms. Every single individual among hermaphrodites produces within itself materials of both sexes--egg and sperm. In most of the higher plants every blossom contains both the male organs (stamen and anther) and the female organs (style and germ). Every garden-snail produces in one part of its sexual gland eggs, and in another sperm. Many hermaphrodites can fructify themselves; in others, however, copulation and reciprocal fructification of both hermaphrodites are necessary for causing the development of the eggs. This latter case is evidently a transition to sexual separation (gonoehorismus).

Out of the members of the last group arose animals with skulls or craniata, having round mouths, and which are divided into hags and lampreys. The hags (myxinoides) have long cylindrical worm-like bodies. The lampreys (petromyxontes) includes those well known "nine eyes" common at the seaside.

These single-nostril animals (monorrhina) arose during the primordial period out of the skull-less animals by the anterior end of the dorsal marrow developing into the brain, and the anterior end of the dorsal skull into the skull. By the division of the single nostril of the members of the last group into two lateral halves, by the formation of a sympathetic nervous system, a jaw skeleton, a swimming bladder and two pairs of legs (breast fins or fore-legs, and ventral fins or hind-legs), arose the primæval fish (selachii), which is best represented by the still-living shark (squalacei).

Out of the primæval fish arose the mud-fish (dipneusta), which is very imperfectly represented by the still-living salamander fish; the primæval fish adapting itself to land, and by the transforming of the swimming bladder into an air-breathing lung, and of the nasal cavity (which was now open into the mouth cavity) into air-passages. Their organization might, in some respect, be like the ceratodus and proloptems; but this is not certain.

The dipneusta is an intermediate stage between the selachii and amphibia. Out of the dipneusta arose the class of amphibia, having five toes (the pentadactyla). The gill amphibians are man's most ancient ancestors of the class amphibia. Besides possessing lungs as well as the mud-fish, they retain throughout life regular gills like the still-living proteus and axolotl. Most gilled batrachia live in North America. The paddle-fins of the dipneusta changed into five-toed legs, which were afterwards transmitted to the higher vertebrata up to man.

The gilled amphibia (sozobrachia) of the last group finally lost their gills but retained their tail, and tailed amphibians (sozura) were produced, such as the salamander and newt of the present day. Out of the sozura originated the primæval amniota (protamnia) by the complete loss of the gills by the formation of the amnion of the cochlea, and of the round window in the auditory organ, and of the organ of tears. Out of the protamnia originated the primary mammals (promammalia). The most closely related were the ornithostoma; they differed through having teeth in their jaws.

No fossil remains of the primary mammals have as yet been found, although they lived during the trias period--they possessed a very highly developed jaw. From the primary mammal arose the pouched animals (marsupialia). Numerous representatives of this group still exist: kangaroos, pouched rats and pouched dogs. The marsupial animals developed, very probably, in the mesolithic epoch (during the Jura) out of the cloacal animals; by the division of the cloaca into the rectum and the urogenital sinus, by the formation of a nipple on the mammary gland, and the partial suppression of the clavicles.

From the marsupialia originated a most interesting small group of semi-apes (prosimiæ), for they are the primary forms of genuine apes and consequently of man. They developed out of handed or ape-footed marsupials (pedumana), of rat-like appearance, by the formation of a placenta, the loss of the marsupium and the marsupial bones, and by the higher development of the commissures of the brain. The still-living short-footed semi-ape (brachytarsi), especially the muki, indie and lori, possess possibly a faint resemblance.

Out of the semi-apes developed two classes of genuine apes; but as the narrow-nosed or catarrhini class are the only ones related to man, the others will not be considered. These narrow-nosed apes originated by the transformation of the jaw, and by the claws on the toes changing into nails. The still-living long-tail nose-apes and holy apes (semnopithecus) probably resembled the oldest ancestors of this group.

The tailed apes by the loss of their tail and some of their hair covering, and by the excessive development of that portion of their brain above the facial portion of the skull, developed into the man-like apes (anthropoides)--such as the gorilla and chimpanzee of Africa, and the orang and gibbon of Asia. The human ancestors of this group existed during the miocene period. From the anthropoides developed the ape-like men (pithecanthropi) during the tertiary period. The speechless primæval men (alali), then, is the connecting link between the man-like apes and man. The fore-hand of the anthropoides became the human hand, their hinder-hand a foot for walking. They did not possess the articulate human language of words and the higher developments, as consciousness and the formation of ideas must have been very imperfect.

Out of the pithecanthropi men developed genuine man, by the development of the animal language of sounds into a connected or articulate language of words--the brain also developed higher and higher. This transition took place, probably, at the beginning of the quaternary period, or possibly in the tertiary.

We have now very briefly reviewed the principal outlines of the ancestors of man, showing that man has developed from the little mass of protoplasm, as have all animals and plants. He therefore was not spontaneously created, but was developed. The question is often asked by simple-minded people, with much delight, Why do we not behold the interesting spectacle of the transformation of a chimpanzee into a man, or conversely of a man by retrogression into an orang?--it only shows that they are not acquainted with the first principles of the Doctrine of Descent. "Not one of the apes," says Schmidt, "can revert to the state of his primordial ancestors, except by retrogression--by which a primordial condition is by no means attained--he cannot divest himself of his acquired characters fixed by heredity, nor can he exceed himself and become man; for man does not stand in the direct line of development from the ape. The development of the anthropoid apes has taken a lateral course from the nearest human progenitors, and man can as little be transformed into a gorilla as a squirrel can be changed into a rat."

"Feeling evidently," says Haeckel, "rather than understanding, induces most people to combat the theory of their 'descent from apes.' It is simply because the organism of the ape appears a caricature of man, a distorted likeness of ourselves in a not very attractive form; because the customary æsthetic ideas and self-glorification of man are touched by this in so sensitive a point, that most men shrink from recognizing their descent from apes. It seems much pleasanter to be descended from a more highly developed divine being, and hence, as is well known, human vanity has from the earliest times flattered itself by assuming the original descent of the race from gods or demi-gods."

EVOLUTION.

In the last chapter a description was given of the various stages in man's development, from the microscopic monad up. It will be necessary now to describe briefly the various laws which have governed this evolutionary chain from the monad to man. But before proceeding directly to the subject, let us look at the doctrine of evolution as a whole, and trace it first in the formation of the world.

The doctrine of evolution is also called the theory of development--it must not, however, be confused with Darwinism--for they are not exactly synonymous. Darwinism is an attempt to explain the laws or manner of evolution. Strictly speaking, only the theory of selection should be called Darwinism, which was established in 1859. The theory of descent, or transmutation theory, or doctrine of filiation, should properly be called Lamarckism, who for the first time worked out the theory of descent as an independent scientific theory of the first order, and as the philosophical foundation of the whole science of biology.

"According to the theory of development (evolution) in its simplest form," says Henry Hartshorne, "the universe as it now exists is a result of 'an immense series of changes,' related to and dependent upon each other as successive steps, or rather growths, constituting a progress; analogous to the unfolding or evolving of the parts of a growing organism." Herbert Spencer defined evolution as consisting in a progress from the homogeneous to the heterogeneous, from general to special, from the simple to the complex; and this process is considered to be traceable in the formation of worlds in space, in the multiplication of the types and species of plants and animals on the globe, in the origination and diversity of languages, literature, arts and sciences, and in all changes of human institutions and society.

Let us now apply this theory of evolution to the physical world. No determined opposition by the mass of people is likely to be manifested to the doctrine of evolution as applied to the physical world, or even to the vegetable or animal world up to man; but the minute man is included--then is a voice raised up against it, and it was for this reason that Darwin in his first work on the "Theory of Descent" did not mention man as being included in the evolutionary series. He knew too well the foolish human weakness that existed.

In a recent work by Prof. Challes, he states that he regards the material universe as "a vast and wonderful mechanism of which the least wonderful thing is its being so constructed that we can understand it."

The following is a brief description of the various theories of the world's formation:

First Theory.--By the first theory the world is supposed to have existed from eternity under its actual form. Aristotle embraced this doctrine, and conceived the universe to be the eternal effect of an eternal cause; maintaining that not only the heavens and the earth, but all animate and inanimate beings, are without beginning. To use Huxley's illustration: If you can imagine a spectator on the earth, however far back in time, he would have seen a world "essentially similar, though not perhaps in all its details, to that which now exists. The animals which existed would be the ancestors of those which now exist, and like them; the plants in like manner would be such as we have now, and like them; and the supposition is that, at however distant a period of time you place your observer, he would still find mountains, lands, and waters, with animal and vegetable products flourishing upon them and sporting in them just as he finds now." This theory being perfectly inconsistent with facts, had to be abandoned.