« ПредыдущаяПродолжить »
ROM the earliest living material, the primeval grain of protoplasm that came to earth we
know not how, some million forms of life have evolved, the lower and simpler forms being ever succeeded by the higher and more complex. From the green cells that multiplied on the tepid mud that fringed the oceans came all the plants that have existed in the past and that now clothe the dry land or live in the water. Family after family arose, more complex and more perfect in structure than those that had preceded it, and dominated the plant world until another appeared with some adaptation to environment which made it better fitted to thrive and multiply. At last the higher flowering plants, the crown of plant evolution, came, with their varied and exquisite devices for securing the continuance of their species, dominated all the earlier evolved families, and filled the earth with their beauty.
From the single cells that were the first animals came all the families that, increasing in complexity and perfection of structure, successively dominated the animal world-all from first to last dependent upon plants for their life. Man, the highest manifestation of life upon this earth, arose from the same lowly beginnings as the humblest form of it. So much the mo wonderful is his development at its highest.
“Man," says Darwin, “bears in his bodily structure clear traces of his descent from lower forms." He is formed on the same general plan as other mammals. His bones can be compared with the corresponding bones of a monkey, dog, bat, or whale. Going outside the special group to which he belongs, we find the most striking structural resemblances through all the backboned animals. The arm of a frog, the wing of a bird, the fore-leg of a dog, the wing of a bat, the flipper of a seal, and the arm of a man are essentially the same, not only in bones but in muscles, nerves, and blood-vessels. Environment has resulted in the evolution from the same structural plan and out of the same material of the form of limb that will serve its possessor best. That the brain of all animals should have arisen probably out of a habit formed by worms of moving with one part of the body always foremost is not more difficult to conceive than that the first glimmerings of animal intelligence should have developed by infinitely slow stages into the highly organized brains of birds and mammals or that the brain of modern man should differ as greatly in power as that of a Newton, for instance, from that of an Australian aboriginal.
Man's first origin among the mammals is obscure, but there seems no doubt that he sprang from the stock from which lemurs, apes, and monkeys are also derived. His nearest relations are the man-like apes, the gorilla, chimpanzee, gibbon, and orang. He is not descended from these but from a stock common to him and them, and apart from his adaptation to an always upright gait his skeleton is essentially identical with theirs.
The ancestors of all the mammals, as has been said, were probably little lemur-like tree-dwellers living in swampy forests. Their descendants who clung to the forest instead of taking to a life on the plains gave rise to ape-like animals from which were derived monkeys,
apes, and, in all probability, man. Just as all the mammal group arose with a tendency to great increase in the size and complexity of the brain, so, we may reasonably believe, in a particular branch of the stock from which the ape-like animals all arose this tendency
was so strong that it produced a brain incomparably superior to that of any other animal, and thus made man. Development in the apes and monkeys took the form of a slow improvement in the brain and a great increase in the power for offence and defence of jaws, teeth, and
Man's intelligence taught him to fashion and use more effective weapons than his natural ones, and his development along ape
lines was checked. LEMUR
The fossil remains of the early forest mammals show that most of them at any rate were essentially similar to the lemurs which still exist in the forests of Southern Africa, Southern Asia, and Madagascar. Modern lemurs are small, but the skull of one extinct species is fifteen inches in length, and many lemurs which survived till recent times were comparatively large. They vanished from the Northern Hemisphere early in mammal history, and in the southern parts of Europe and North America their place was taken by monkeys, animals of distinctly greater brain-power.
American monkeys differ from those of the Old World in their teeth, their prehensile tails, and the flattening and widening of the nose. They never produced great apes or made any approach to the human stock. All the Old World monkeys resemble man in their teeth and in their comparatively narrow nose, with the nostrils opening downward. None of them have prehensile tails, and many have no tails at all. One family, the manlike apes, represented at the present time by the gorillas and chimpanzees of tropical Africa, and the orangs and gibbons of South-east Asia, resembles man very closely in many respects. In the earlier days of the family it spread as far north as the middle of Europe, for the fossil remains of several man-like apes are found in the rocks of France, Northern Spain, Germany, and Austria. The climate of Europe cooled, becoming temperate and then passing through an ice period, and the apes retreated southward to warmer lands. As they disappeared from Europe long before the appearance of man, it is in the rocks of more tropical countries that we must look for the links between man and the early apes. So far only one discovery of this kind has been made in the tropics, and the interpretation of the remains found in river-drift in Java remains doubtful.
They consist of the roof of a skull, two grinding teeth, and a thigh-bone, and they are considered by some to represent a link between the gibbons and man. The roof of the skull is very like that of the existing gibbons of Java. It has a low crown and prominent browridges, but it is almost as large as the skull of a small man and the brain capacity is almost human. On the other hand, the teeth are more like those of a gibbon than those of a man. The thigh-bone is adapted for upright gait, but is not completely human. It is
doubtful whether these fragmentary remains are those of an ancestral man or of a very large and highly developed gibbon. The direct progenitors of man have yet to be discovered, but somewhere the rocks hold their remains, as well as those of the ancestors of men and apes alike.
Even the largest man-like apes are much inferior to man in brain capacity. In modern Europeans this averages 1480 c.c. ; in the largest ķnown gorilla it is not more than 600 c.c. Brain development is often found accompanying increased powers of balance and locomotion, and man's adoption of an upright gait was probably the most decisive step in his evolution, since it freed his hands first to fashion and use weapons instead of being dependent upon his own jaws, teeth, and muscular grip for fighting purposes, and secondly to acquire in due course all the manual arts. As he gradually formed the habit of fighting his enemies with stones and clubs the great canine teeth which are characteristic of apes and monkeys would become reduced in size, and the jaws would be modified so that articulate speech became possible. Adaptations of structure would take place as an upright posture became habitual, rendering it more easy to maintain, in particular, a curving of the backbone and a poise of the head different from that of apes. In the man-like species, though an upright gait is possible, the straight spine, the overweighted front portion of the head, and the over-developed arms cause them to vary in their mode of progression between the use of hind-legs only and of all-fours. Lastly, though they have been known to unite in repelling an attack, the man-like apes do not, as some monkeys do, live in societies, and it is man's social habits that more than any other factor in his