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.”
Fossils have been found showing several gradations or stages in development intermediate between man and his pre-human ancestor—evidences which, if they do not completely bridge the chasm, stand as ruined pillars, broken arches, isolated spans of the bridge over which man was many hundreds of thousands of years in crossing.
The first skull discovered (sixty years ago) of the Neanderthal men was so entirely different from other pre-historic skulls that one scientist declared it was a mal-formation; but other fossils were found later that proved the peculiarities to be racial characteristics. These men, who lived in Europe down to thirty thousand years ago, were squat, bent-kneed, thick-skulled, almost chinless, and with ridge-like projections over deep-set eyes. In skull development they were lower than any savage of today.
Older than the Neanderthal race, and lower in the human scale, were the Heidelberg men, said to have been the first really human beings of whom we have fossil evidences. Judging from the age of the fossil beds they existed from 100,000 to 200,000 years ago.
Thirty years ago were found some of the fossil remains of a creature in Java, some forty feet below the surface, that show characters intermediate between the gorilla and the Neanderthal man; “the lowest human cranium yet described, very nearly as much below the Neanderthal as this is below the normal European.” This creature was named Pithecanthropus Erectus (erect ape-man).
Lack of space prevents even a brief description of other and intermediate types of man, such as the man of Spy, of Naulette, of Predmost, etc.
As the more man develops (becomes specialized) the farther he is removed from the lower animals, so, in tracing his descent toward his origin we find him approaching them, apes included, in general characteristics, for we approach the point of divergence.
Evolution is a fact. There is no doubt of that in the minds of those who have investigated the subject without prejudice and with the acquisition of truth as the sole aim. One may dispute a fact, but he cannot deny it out of existence. Those who feel a sense of shame for their close proximity to their cousin, the monkey, are advised to increase that distance by carrying to higher development those traits considered peculiarly human: Reason, a sense of justice, of broader sympathy, and tolerance.
By his great discovery Darwin delivered the heaviest solar plexus blow to human vanity it ever received. For this he deserves, and receives, the eternal gratitude of every right-thinking man and woman.
How was evolution brought about? What are its laws, and how do they work?