Part 8

When an organism has been subjected to abnormal conditions in life it can transmit any peculiarity it may have acquired. This is, however, not always possible, otherwise descendants of men who have lost their arm or leg would be born without the corresponding arm or leg--this shows that some acquired qualities are more easily transmitted than others--although there are cases, as, for instance, a race of dogs without tails has been produced by cutting off the tails of both sexes of the dog, during several generations. "A few years ago," says Haeckel, "a case occurred on an estate near Jena in which, by the careless slamming of a stable-door, the tail of a bull was wrenched off, and the calves begotten by this bull were all born without a tail. This is certainly an exception; but it is very important to note the fact that under certain unknown conditions such violent changes are transmitted in the same manner as many diseases." The transmission of diseases such as consumption, madness, and albinism form examples. Albinoes are those individuals who are distinguished by the absence of coloring matter from their skins; they are of frequent occurrence among men, animals and plants. Among many animals, such as rabbits and mice, albinoes with white fur and red eyes are so much liked that they are propagated. This would be impossible were it not for the law of the transmission of adaptations. Hornless cattle have descended from a single bull born in 1770 of horned parents, but whose absence of horns was the result of some unknown cause.

The law of interrupted or latent transmission, as illustrated in grandchildren who are like the grandparents, but quite unlike the parents. Animals often resume a form which have not existed for many generations. One of the most remarkable instances of this kind of reversion, or "atavism," is the fact that in some horses there sometimes appear singular dark stripes similar to those of the zebra, quagga, and other wild species of African horse.

Nutrition directly modifies adaptation, as is well illustrated by animals which have been bred for domestic or other purposes. If a farmer is breeding for fine wool he gives much different food to the sheep than he would if he wished to obtain flesh or an abundance of fat. Even the bodily form of man is quite different according to its nutrition. Food containing much nitrogen produces little fat, that containing little nitrogen produces a great deal of fat. People who by means of Banting's system, at present so popular, wish to become thin, eat only meat and eggs--no bread, no potatoes.

Man can breed for milk in cattle, for feathers in pigeons, for colored flowers in plants, and, in fact, for almost any desirable quality.

GEOLOGICAL RECORD.

The Geological Record (palæontology) furnishes weighty evidence of man's descent; for the circumstantial evidence derived from this source is written without the possibility of a mistake, with no chance of error, on the stratified rocks. It is true that the geological record must be incomplete, because it can only preserve remains found in certain favorable localities, and under particular conditions; that this valuable record must be destroyed by processes of denudation, and obliterated by processes of metamorphosis, it cannot be doubted. "Beds of rock of any thickness, crammed full of organic remains, may yet," says Huxley, "by the percolation of water through them, or the influence of subterranean heat (if they descend far enough toward the centre of the earth), lose all trace of these remains, and present the appearance of beds of rock formed under conditions in which there was no trace of living forms. Such metamorphic rocks occur in formations of all ages; and we know with perfect certainty, when they do appear, that they have contained organic remains, and that those remains have been absolutely obliterated." If we look at the geological record, we find:

THE FIRST EPOCH.--The Archilithic, or Primordial Epoch, constitutes the Age of Skull-less Animals and Sea-weed Forests, and is made up of the Laurentian, Cambrian, and Silurian Period.

THE SECOND EPOCH.--The Palæolithic, or Primary Epoch, constitutes the Age of Fishes and Fern Forests, and is made up of the Devonian, Coal, and Permian Period.

THE THIRD EPOCH.--The Mesolithic, or Secondary Epoch, constitutes the Age of Reptiles and Pine Forests, Coniferæ, and is made up of the Triassic, Jurassic, and Chalk Period.

THE FOURTH EPOCH.--The Cænolithic, or Tertiary Epoch, constitutes the Age of Mammals and Leaf Forests, and is made up of the Eocene, Miocene, and Phocene Period.

THE FIFTH EPOCH.--The Anthropolithic, or Quaternary Epoch, constitutes the Age of Man and Cultivated Forests, and is made up of the Glacial and Postglacial Period, and the Period of Culture.

During the archilithic epoch the inhabitants of our planet, as has been already stated, consisted of skull-less animals, or aquatic forms. No remains of terrestrial animals or plants, dated from this period, have as yet been found.

The archilithic period was longer than the whole long period between the close of the archilithic and the present time; for if the total thickness of all sedimentary strata be estimated as about one hundred and thirty thousand feet, then seventy thousand feet belong to this epoch. It was during this epoch that the little mass of protoplasm, which has been so often spoken of, came into existence.

It has been stated above that palæontology is quite deficient. This is not only true of the record, but of the lack as yet of sufficient investigations. The greatest fields of investigation in this department have never been explored. The whole of the petrifactions accurately known do not probably amount to a hundredth part of those which, by more elaborate explorations, are yet to be discovered. The most ancient of all distinctly preserved petrifactions is the Eozoon Canadense, which was found in the lowest Laurentian strata in the Ottawa formation.

Probably no discovery in palæontology ranks higher than the discovery of the descendants of the horse. The horse, for example, as far as his limbs and teeth go, differs far more from extant graminivora than man differs from the ape. Had not fossil ungulates been found, which demonstrate the common origin of the horse with didactyles and multidactyles, some would have deemed the horse a special miraculous creation. But now the links are complete, and the descent of the horse is found to follow exactly what the doctrine of evolution could have predicted.

ONTOGENY.

It has been stated that the palæontological record is quite incomplete, owing to many facts, some of which have been mentioned; fortunately, the history of the development of the organic individual, or ontogeny, comes in to fill up many deficiencies.

Ontogeny is a repetition of the principal forms through which the respective individuals have passed from the beginning of their tribe, and its great advantage is that it reveals a field of information which it was impossible for the rocks to retain; for the petrification of the ancient ancestors of all the different animal and vegetable species, which were soft, tender bodies, was not possible.

The annexed plate illustrates the dog, rabbit, and man in their first stages of development. Illustrations of a fish, an amphibious animal, a reptile, a bird, or any mammal, could also be given; for all vertebrate animals of the most different classes, in their early stages of development, cannot be distinguished, and the nearer the animal approaches man in the ascending scale, the longer does this similarity continue to exist--when reptiles and birds are distinctly different from mammals, the dog and the man are almost identical.

The gill-arches of the fish exist in man, in dogs, in fowls, in reptiles, and in other vertebrate animals during the first stages of their development. Man also possesses, in his first stages, a real tail, as well as his nearest kindred--the tailless apes (orang-outang, chimpanzee, gorilla), and vertebrate animals in general. The tail, as has been stated, man still retains, though hidden as a rudiment.

"Man presents in his earliest stages of embryonic growth, a skeleton of cartilage, like that of the lamprey; also, five origins of the aorta and five slits on the neck, like the lamprey and the shark. Later, he has but four aortic origins, and a heart now divided into two chambers, like bony fishes; the optic lobes of his brain also having a very fish-like predominance in size. Three chambers of the heart and three aortic origins follow, presenting a condition permanent in the batrachia; then two origins with enlarged hemispheres of the brain, as in reptiles. Four heart chambers and one aortic root on each side, with slight development of the cerebellum, agree with the characters of the crocodiles, and immediately present the special mammalian conditions, single aortic root, and the full development of the cerebellum. Later comes that of the cerebrum, also in its higher mammalian or human traits." At no time in the development of the egg, save at the start, do the embryos of the various vertebra assume the exact or entire characteristics of one another, but they assimilate so closely that it requires the eye of the expert to distinguish them; and, as has already been stated, the more closely an animal resembles another, the longer and the more intimately do their embryos resemble one another; so that, for example, the embryo of the snake and of a lizard remain like one another longer than do those of a snake and of a bird; and the embryo of a dog and of a cat remain like one another for a far longer period than do those of a dog and a bird, or a dog and an opossum, or even those of a dog and a monkey.

Surely it must be admitted that the short brief history given by the development of the egg, is far more wonderful than phylogeny or the long and slow history of the development of the tribe, which has taken thousands of years. Compare this time with the time required for the development of the smallest mammals--the harvest mice which develops in three weeks, or the smallest of all birds, the humming-bird, which quits the egg on the twelfth day, or with man who passes through the whole course of his development in forty weeks, or with the rhinoceros who requires 1-1/2 years, or the elephant who requires ninety weeks. How insignificant are these various periods to the long period originally required; yet in these short periods the whole phylogeny is run through in the ontogeny or the history of the development of the egg.

THE ATTRIBUTES OF MAN.

We must now consider briefly some of the attributes of man, and see if he really possesses attributes which are in no inferior degree possessed by animals. Before proceeding directly to the consideration of the attributes of man, it will be best to show the correlation that exists between what are called man's vital forces and the physical forces of nature. To do this let us choose three forms of its manifestation: these shall be heat evolved within the body; muscular energy or motion; and lastly, nervous energy or that form of force which, on the one hand, stimulates a muscle to contract, and on the other appears in forms called mental. It will not take any extensive argument to demonstrate that the heat of the body does not differ from heat from any other source. It is known that the food taken into the body contains potential energy, which is capable of being in part converted into actual heat by oxidation; and since we know that the food taken into the body is oxidized by the oxygen of the air supplied by the lungs, the heat of the body must be due to the slow oxidation of the carbon, perhaps also hydrogen, sulphur, and phosphorus in the food. Now since this so-called vital heat is developed by oxidation, is recognized by the same tests and applied to the same purposes as any other heat, it is as truly correlated to the other forces as when it has a purely physical origin. The amoeboid activity of a white blood corpuscle is stimulated within certain limits by heat. Hatching of eggs and the germination of seeds may be likewise hastened or retarded by access or deprivation of heat. It was considerations such as these which led to the doctrine of correlation of the vital and physical forces.

With respect to the muscular force exerted by an animal, it was supposed that it was created by the animal. Dr. Frankland says to this: "An animal can no more generate an amount of force capable of moving a grain of sand, than a stone can fall upwards or a locomotive drive a train without fuel." As the amount of CO{2} exhaled by the lungs is increased in the exact ratio of work done by the muscle, it cannot be doubted that the actual force of the muscle is due to the converted potential energy of the food. Since every exertion of a muscle and nerves involves the death and decay of those tissues to a certain extent, as shown by the excretions, Prof. Orton has been led to say: "An animal begins to die the moment it begins to live." "A muscle," says Barker, "is like a steam-engine, is a machine for converting the potential energy of carbon into motion; but unlike a steam-engine, the muscle accomplishes this conversion directly, the energy not passing through the intermediate stages of heat. For this reason the muscle is the most economical producer of mechanical force known." The muscles which give the downward stroke of the wing of a bird are fastened to the breastbone, and their power in proportion to the weight of the bird is as 10,000 to 1. This great power is needed, for the air is 770 times lighter than water; the hawk being able to travel 150 miles an hour.

The last of the so-called vital forces under consideration, is that produced by the nerves and nervous centres. Barker says: "In the nerve which stimulates a muscle to contract, this force is undeniably motion, since it is propagated along this nerve from one extremity to the other." This force has been likened unto electricity, the gray or cellular matter being the battery, the white or fibrous matter the conductors. Du Bois Reymond has demonstrated that this force is not electricity, though by showing that its velocity is only ninety-seven feet a second. The velocity varies, though, in different animals; it is, according to Prof. Orton, "more rapid in warm-blooded than in cold-blooded animals, being nearly twice as fast in man as in the frog." Wheatstone, by his method, gives the velocity of electricity in copper wire at 62,000 geographical miles per second; but as neither Fizeau, Gould, Gonnelle and others could arrive at the same result, the method was shown to be incorrect, and it remained for Dr. Siemen to discover the true method, which gives the velocity just one-half that of Wheatstone's estimate, or 31,000 geographical miles per second. In the opinion of Bence Jones, the propagation of a nervous impulse is a sort "of successive molecular polarization, like magnetism." But that this agent is a force as analogous to electricity as is magnetism, is shown not only by the fact that the transmission of electricity along a nerve will cause the contraction of a muscle to which it leads, but also by the important fact discovered by Marshall, that the contraction of a muscle is excited by diminishing its normal electrical current, a result which could take place only with a stimulus, says Barker, "closely allied to electricity. Nerve force must therefore be transmuted potential energy." Prof. Huxley says, "the results of recent inquiries into the structure of the nervous system of animals, converge toward the conclusion that the nerve-fibres which we have hitherto regarded as ultimate elements of nervous tissue, are not such, but are simply the visible aggregations of vastly more attenuated filaments, the diameter of which dwindles down to the limits of our present microscopic vision, greatly as these have been extended by modern improvements of the microscope; and that a nerve is, in its essence, nothing but a linear tract of specially modified protoplasm between two points of an organism, one of which is able to affect the other by means of the communication so established. Hence it is conceivable that even the simplest living being may possess a nervous system."

Herbert Spencer says all direct and indirect evidence "justifies us in concluding that the nervous system consists of one kind of matter. In the gray tissue this matter exists in masses containing corpuscles, which are soft and have granules dispersed through them, and which, besides being thus unstably composed, are placed so as to be liable to disturbances to the greatest degree. In the white tissue this matter is collected together in extremely slender threads that are denser, that are uniform in texture, and that are shielded in an unusual manner from disturbing forces, except at their two extremities."

The last consideration is that form of force (thought power) which appears in manifestations called mental. It must be noticed at the outset, that every external manifestation of thought force is a muscular one, as a word spoken or written, a gesture, or an expression of the face always takes place; hence this force must be intimately correlated to nerve force. It is very certain, then, that thought force is capable in external manifestations of converting itself into actual motion. But here the question arises, can it be manifested inwardly without such a transformation of energy? Or is the evolution of thought entirely independent of the matter of the brain?