In our last lesson we led you by successive steps from the beginnings of Life in living forms up to the creatures closely resembling the family of vertebrates–the highest family of living forms on this planet. In this present lesson we take up the story of the “Ascent of Man” from the lowly vertebrate forms.
The large sub-family of forms called “The Vertebrates” are distinguished from the Invertebrates by reason of the former possessing an internal bony skeleton, the most important feature of which is the vertebra or spinal column. The vertebrates, be it remembered, possess practically the same organs as the lower forms of life, but differ from them most materially by the possession of the internal skeleton, the lower forms having an external or outside skeleton, which latter is merely a hardening of the skin.
The flexibility of the vertebra creates a wonderful strength of structure, combined with an ease of movement peculiar to the vertebrates, and which renders them the natural forms of life capable of rapid development and evolution. By means of this strength, and ease, these forms are enabled to move rapidly in pursuit of their prey, and away from their pursuers, and also to resist outside pressure or attack. They are protected in a way similar to the invertebrates having shells, and yet have the additional advantage of easy movement. Differing in shape and appearance as do the numerous members of the sub-family of vertebrates, still their structure is easily seen to spring from a single form–all are modifications of some common pattern, the differences arising from the necessities of the life of the animal, as manifested through the desire and necessities of the species.
Science shows the direct relationship between the Vertebrates, and the Invertebrates by means of several connecting-links, the most noticeable of which is the Lancelot, a creature resembling the fish-form, and yet also closely resembling the lower (invertebrate) forms of life. This creature has no head, and but one eye. It is semi-transparent, and possesses cilia for forcing in the water containing its food. It has something like gills, and a gullet like the lower forms. It has no heart, the blood being circulated by means of contracting vessels or parts. Strictly speaking, it has no back-bone, or vertebra, but still Science has been compelled to class it among the vertebrates because is has a gristly cartilage where the back-bone is found in the higher forms. This gristle may be called an “elementary spine.” It has a nervous system consisting of a single cord which spreads into a broadened end near the creature’s mouth, and which may therefore be regarded as “something like a brain.” This creature is really a developed form of Invertebrate, shaped like a Vertebrate, and showing signs of a rudimentary spine and nervous system of the latter. It is a “connecting-link.”
The lowest forms of the true Vertebrates are the great families of Fishes. These Fish families include fishes of high and low degree, some of the higher forms being as different from the lowest as they (the highest) are different from the Reptile family. It is not necessary to go into detail regarding the nature of the fish families, for every student is more or less familiar with them.
Some peculiar forms of fish show a shading into the Reptile family, in fact they seem to belong nearly as much to the latter as to their own general family. Some species of fish known as the Dipnoi or “double-breathers,” have a remarkable dual system of breathing. That is, they have gills for breathing while in the water, and also have a primitive or elementary “lung” in the shape of an air-bladder, or “sound,” which they use for breathing on land. The Mud-fish of South America, and also other forms in Australia and other places, have a modification of fins which are practically “limbs,” which they actually use for traveling on land from pond to pond. Some of these fish have been known to travel enormous distances in search of new pools of water, or new streams, having been driven from their original homes by droughts, or perhaps by instincts similar to the migrating instinct of birds.
Eels are fish (although many commonly forget this fact) and many of their species are able to leave the water and travel on land from pond to pond, their breathing being performed by a peculiar modification of the gills. The climbing perch of India are able to live out of water, and have modified gills for breathing purposes, and modified fins for climbing and walking. So you see that without leaving the fish family proper, we have examples of land living creatures which are akin to “connecting links.”
But there are real “connecting-links”‘ between the Fish and the Reptiles. Passing over the many queer forms which serve as links between the two families, we have but to consider our common frog’s history for a striking example. The Tadpole has gills, has no limbs, uses its tail like a fish’s fin, eats plants, etc. Passing through several interesting stages the Tadpole reaches a stage in which it is a frog with a tail–then it sheds its tail and is a full fledged Frog, with four legs; web-feet; no tail; and feeding on animals.
The Frog is amphibious, that is, able to live on land or in water–and yet it is compelled to come to the surface of the water for air to supply its lungs. Some of the amphibious animals possess both lungs and gills, even when matured; but the higher vertebrates living in the water breathe through lungs which are evolved from the air-bladder of fishes, which in turn have been evolved from the primitive gullet of the lower forms. There are fishes known which are warm-blooded. Students will kindly remember that the Whale is not a fish, but an aquatic animal–a mammal, in fact, bringing forth its young alive, and suckling it from its breasts.
So we readily see that it is but a step, and a short step at that, between the land-traveling and climbing fishes and the lower forms of Reptiles. The Frog shows us the process of evolution between the two families, its life history reproducing the gradual evolution which may have required ages to perfect in the case of the species. You will remember that the embryo stages of all creatures reproduce the various stages of evolution through which the species has passed–this is true in Man as well as in the Frog.
We need not tarry long in considering the Reptile family of living forms. In its varieties of serpents, lizards, crocodiles, turtles, etc., we have studied and observed its forms. We see the limbless snakes; the lizards with active limbs; the huge, clumsy, slow crocodiles and alligators–the armor-bearing turtles and tortoises–all belonging to the one great family of Reptiles, and nearly all of them being degenerate descendants of the mighty Reptile forms of the geological Age of Reptiles, in which flourished the mighty forms of the giant reptiles–the monsters of land and water. Amidst the dense vegetation of that pre-historic age, surrounded by the most favorable conditions, these mighty creatures flourished and lived, their fossilized skeleton forms evidencing to us how far their descendants have fallen, owing to less favorable conditions, and the development of other life-forms more in harmony with their changed environment.
Next comes the great family of Birds. The Birds ascended from the Reptiles. This is the Eastern Teaching, and this is the teaching of Western Science It was formerly taught in the text-books that the line of ascent was along the family of winged reptiles which existed in the Age of Reptiles, in the early days of the Earth. But the later writers on the subject, in the Western world, have contradicted this. It is now taught that these ancient winged-reptiles were featherless, and more closely resembled the Bat family than birds. (You will remember that a Bat is neither a reptile nor a bird–it is a mammal, bringing forth its young alive, and suckling them at its breast. The Bat is more like a mouse, and its wings are simply membrane stretched between its fingers, its feet, and its tail.)
The line of ascent from Reptile to Bird was along the forms of the Reptiles that walked on land. There are close anatomical and physiological relations and correspondences between the two families (Reptiles and Birds) which we need not refer to here. And, of course, many modifications have occurred since the “branching-out.” The scales of the reptiles, and the feathers of the birds, are known to be but modifications of the original outer skin, as are also the hair, claws, hoofs, nails, etc., of all animals. Even teeth arose in this way, strange as it may now seem–they are all secreted from the skin. What a wonderful field for thought–this gradual evolution from the filmy outer covering of the lowest living forms to the beautiful feathers, beaks, and claws of the bird!
The evolving of wings meant much to the ascending forms of life. The Reptiles were compelled to live in a narrow circle of territory, while the Birds were able to travel over the earth in wide flights. And travel always develops the faculties of observation, memory, etc., and cultivates the senses of seeing, hearing, etc. And the creature is compelled to exercise its evolving “thinking” faculties to a greater extent. And so the Birds were compelled by necessity of their travels to develop a greater degree of thinking organism. The result is that among birds we find many instances of intelligent thought, which cannot be dismissed as “mere instinct.” Naturalists place the Crow at the head of the family of Birds, in point of intelligence, and those who have watched these creatures and studied the mental processes, will agree that this is a just decision. It has been proven that Crows are capable of counting up to several figures, and in other ways they display a wonderful degree of almost human sagacity.
Next above the Bird family comes the highest form of all–the Mammals. But before we begin our consideration of these high forms, let us take a hasty glance at the “connecting-links” between the Birds and the Mammals. The lowest forms of the Mammals resemble Birds in many ways. Some of them are toothless, and many of them have the same primitive intestinal arrangements possessed by the birds, from which arises their name, Monotremes. These Monotremes may be called half-bird and half-mammal. One of the most characteristic of their family is the Ornithorhynchus, or Duck-bill, which the early naturalists first thought was a fraud of the taxidermists, or bird-stuffers, and then, when finally convinced, deemed it a “freak-of-nature.” But it is not a freak creature, but a “connecting-link” between the two great families of creatures. This animal presents a startling appearance to the observer who witnesses it for the first time. It resembles a beaver, having a soft furry coat, but also has a horny, flat bill like a duck, its feet being webbed, but also furnished with claws projecting over the edge of the web-foot.
It lays eggs in an underground nest–two eggs at a time, which are like the eggs of birds, inasmuch as they contain not only the protoplasm from which the embryo is formed, but also the “yolk.” on which the embryo feeds until hatched. After the young Duck-bill is hatched, it feeds from teatless glands in the mother’s body, the milk being furnished by the mother by a peculiar process. Consider this miracle—an animal which lays eggs and then when her young are hatched nourishes them with milk. The milk-glands in the mother are elementary “breasts.”
The above-mentioned animal is found in Australia, the land of many strange forms and “connecting-links,” which have survived there while in other parts of the globe they have vanished gradually from existence, crowded out by the more perfectly evolved forms. Darwin has called these surviving forms “living fossils.” In that same land is also found the Echidna or spiny ant-eater, which lays an egg and then hatches it in her pouch, after which she nourishes it on milk, in a manner similar to that of the Duck-bill. This animal, like the Duck-bill, is a Monotreme.
Scientists are divided in theories as to whether the Monotremes are actually descended directly from the Reptiles or Birds, or whether there was a common ancestor from which Reptiles and Birds and Mammals branched off. But this is not important, for the relationship between Reptiles, Birds and Mammals is clearly proven. And the Monotremes are certainly one of the surviving forms of the intermediate stages.
The next higher step in the ascent of Mammal life above the Monotreme is occupied by the Marsupials, or milk-giving, pouched animals, of which family the opossum and kangaroo are well known members. The characteristic feature of this family of creatures is the possession of an external pouch in the female, in which the young are kept and nourished until they can take care of themselves as the young of other animals are able to do. The young of the Marsupials are brought forth, or born, in an imperfect condition, and undeveloped in size and strength.
There are fossil remains of Marsupials showing that in past ages creatures of this kind existed which were as large as elephants. In the more common form of Mammals the young are brought forth fully formed, they having received “nourishment, before birth, from the mother’s body, through the placenta, the appendage which connects the fetus with the parent. The Placental Mammals were the best equipped of all the life-forms for survival and development, for the reason that the young were nourished during their critical period, and the care that the mammal must of necessity give to her young operated in the direction of affording a special protection far superior to that of the other forms. This and other causes acted to place the Placentals in the “Royal line” from which Man was evolved.
The following families of Placental Mammals are recognized by Science, each having its own structural peculiarities:
The Edentata, or Toothless creatures, among which are the sloths, ant-eaters, armadillos, etc. These animals seem to be closer to the Monotremes than they are to the Marsupials;
The Sirenia, so called by reason of their fanciful resemblance to the sirens of mythology, among which are the sea-cows, manatees, dugongs, etc., which are fish-like in structure and appearance, the fore-limbs being shaped like paddles, or fins, and the hind-limbs being absent or rudimentary;
The Cetacea, or Whale Family, including whales, Porpoises, dolphins, etc., which are quite fish-like in appearance and structure, their forms being adapted for life in the sea, although they are, of course, Mammals, bringing forth matured young which are suckled at the breast;
The Ungulata, or Hoofed Animals, which comprise many varied forms, such as the horse, the tapir, the rhinoceros, the swine, the hippopotamus, the camel, the deer, the sheep, the cow, etc., etc.;
The Hyracoidea, which is a small family, the principal member of which is the coney, or rock rabbit, which has teeth resembling those of the hoofed animals, in some ways, and those of the gnawing animals in the others.
The Proboscidea, or Trunked Animals, which family is represented in this age only by the families of elephants, which have a peculiar appendage called a “trunk,” which they use as an additional limb;
The Carnivora, or Flesh-eaters, represented by numerous and various forms, such as the seal, the bear, the weasel, the wolf, the dog, the lion, the tiger, the leopard, etc. The wolf and similar forms belong to the sub-family of dogs; while the lion, tiger, etc., belong to the sub-family of cats;
The Rodentia, or Gnawers, comprising the rat, the hare, the beaver, the squirrel, the mouse, etc., etc.;
The Insectivora, or Insect Feeders, comprising the mole, the shrew, the hedgehog, etc.;
The Chiroptera, or Finger-Winged Animals, comprising the great family of Bats, etc., which are very highly developed animals;
The Lemuroidea, or Lemurs, the name of which is derived from the Latin word meaning a “ghost,” by reason of the Lemur’s habits of roaming about at night. The Lemur is a nocturnal animal, somewhat resembling the Monkey in general appearance, but with a long, bushy tail and sharp muzzle like a fox. It is akin to a small fox having hands and feet like a monkey, the feet being used to grasp like a hand, as is the case with the true Monkey family. These creatures are classed by some naturalists among the Monkeys by reason of being “four-handed,” while others are disposed to consider as still more important their marked relationship with, and affinity to, the marsupials, gnawers and insect-feeders. On the whole, these creatures are strangely organized and come very near to being a “connecting-link” between other forms. One of the Lemurs is what is known as the colugo, or “flying lemur,” which resembles a squirrel in many particulars, and yet has a membranous web extending from its hands, which enables it to make flying leaps over great distances. This last named variety seems to furnish a link between the insect-feeders and the Primates;
The Primates, which is a large family comprising the various forms of monkeys, baboons, man-apes, such as the gibbon, gorilla, chimpanzee, orang-outang, etc., all of which have big jaws, small brains, and a stooping posture. This family also includes MAN, with his big brain and erect posture, and his many races depending upon shape of skull, color of skin, character of hair, etc.