Popular Science Monthly/Volume 50/February 1897/The Animate World a Unity
|THE ANIMATE WORLD A UNITY.|
THE aspect of paleontology has greatly changed since the time of Cuvier, when species were supposed to be fixed, and the curious monsters whose remains were unearthed from time to time were believed to be unchangeable, isolated entities. Now it is shown that fossil species are not thus independent, but are simply phases of development of types which are carrying on their evolution through the immensity of the ages. A plan has ruled in the vast and magnificent history of this evolution, and I purpose to tell what I believe I have discovered of it. I can not conceal that in the present state of science such an essay will be very imperfect. When I was traveling in the East I found the horizons in the morning veiled by the bluish mist which the poets are so fond of, and tried to discover the silhouettes of the beautiful marble mountains through them. So, in the morning of our paleontological science, we look upon the distances of life vaguely sketched, and try to distinguish a few lines of the plan that rules it. We discern but little, but that little is enough to charm us, as a glimpse of sunshine charms in a dark landscape.
It seems to me, further, that besides its philosophical interest, the inquiry into the plan of creation is of importance in practical geology. Up to this time the determination of the age of the earth has been empirical. It will become rational as soon as we are in possession of the plan of creation. Geologists will recognize that one of the best means of fixing the age of a formation is to know the stage of development of the fossils it contains.
The world of life is a grand unity, of which we can follow the development as we do that of an individual. When we follow the course of the immensity of geological times, we meet successive changes, and our mind goes on from surprise to surprise. Each epoch has its own physiognomy, and each phase of each epoch offers some variation; the days of the world follow one another and are not alike. Yet manifest as are the differences, they are not radical. Paleontology has not discovered any new branching or any new class or subclass.
From the primary ages, animated nature has had general traits of resemblance with existing nature. Sponges and polyps were already forming colonies, echinoderms were divided into five parts, insects were provided with three pairs of legs, arachnids had four, and myriapods had a multitude. M. Bernard Renault found in a coal bed an ostracode, the body of which is entirely preserved. A study of it made by M. Charles Brongniart showed the same details of organization as in our days. Numerous brachiopods belonged to genera which exist in our seas—such as Lingula, Rhynchonella, and Terebratula. Besides fishes of special types, we find some with tendencies toward those of to-day. Prof. Vaillant, examining a Permian genus which I had described under the name of Megopleuron, thought it was so nearly like some living ceratodes of Australia that he proposed to describe it under the same generic name. The Primary reptiles, although very different from those of our epoch, have many characters of resemblance to them. For example, having occasion to study in detail the reptiles of the Permian, I was very much struck by seeing that their heads had the same bones, both above and below, as in the existing animals. MM. Marcellin, Boule, and Glangeaud, comparing the paws of a reptile of the same formation with those of a common varanus, remarked their extreme similitude.
When we come to the Secondary formations, we find many invertebrate animals related to living genera. Most of the vertebrate animals are easily distinguished from present genera, though usually not because they present any unknown special features, but because they combine characteristics that are now distributed among distinct classes. M. Seeley has recently described Triassic quadrupeds from Africa which diminish the distance between the reptiles and the mammals; the icthyosaurus, which is cited as one of the most extraordinary fossils, recalls the fish in its vertebrae, the massive mammals in its fore flippers, and the reptiles in its other characteristics. Although the pterodactyl certainly belongs to the class of reptiles, its manner of flying is like that of flying mammals. The iguanodon is a reptile with its hinder limbs forerunners of those of birds. On the other hand, the archæopteryx is a bird with reptilian recollections. The Secondary fossils, which have surprised paleontologists so much by their singular features, in reality establish connections among animated beings instead of disclosing gaps.
In the Tertiary epoch the existing genera—rhinoceros, tapir, boar, gazelle, elephant, hyena, cat, bear, etc.—appear each in its turn. We find species, as well as genera, so near living forms that it is difficult not to suppose their near relationship.
Finally, the species of Quaternary times are for the most part identical with those of to-day, or so little different that they may be considered simply as races. It is impossible to mark a boundary between beings that existed before us and those that live with us.
It must therefore be recognized that the fossil world is not distinct from the existing world; there is only a single world, which has continued from the most ancient ages till our days. It can be studied as if it were an individual; in the same way as we follow the development of an individual through its different ages, we follow the development of the animate world through the phases of its existence that we call the geological ages.
When an old man feels the weight of years, he realizes indeed that his youth has departed from him; but at what moment did he pass from infancy to youth, and then to maturity and old age? He does not know; the phases of his life have unfolded themselves gradually. Things have gone in the same way for all beings. The world has not to-day the physiognomy it once had, but no one can say in what instant it passed from its Primary condition to its Secondary, and from that to its Tertiary, and then to its Quaternary and present. The change of beings has been slow and gradual.
The development of man—that is, of the individual himself—in which the marvels of the animate world are summarized, presents the following phases: 1. Multiplication of constituent parts—that is, numerous points of ossification appear which will become separate bones. 2. Differentiation of parts. As the parts multiply, they differentiate themselves; thus points of ossification similar in the beginning take on differences as they proceed; one becomes the humerus, another the radius, another the orbital bone, etc. 3. Growth of parts. At the same time that they multiply and differentiate themselves they are growing. 4. Progress of activity. Besides material progress, there is progress of a higher order—from the passive existence within his mother's womb till the individual reaches active life and manifests an energy of his own. 5. Progress of sensibility. Sensibility increases at the same time with activity, and sometimes determines it. 6. Progress of intelligence. Finally, intelligence appears. Last come, it also goes away last with sensibility, and will console the old man in the enfeeblement of his other faculties.
The history of the animate world, considered in the aggregate of geological times, is very similar to the history of a man in his brief life. We may study in succession the multiplication of beings on the surface of the globe; their differentiation; their growth; the progress of activity; the progress of sensibility; and the progress of intelligence.—Translated for the Popular Science Monthly from the Revue des Deux Mondes.