The boldest and most enthusiastic opponents of evolution have always been those with the least information about it. But the evidence is accumulating so rapidly, and is being drawn up in such unanswerable array, that, if it is not already the case, it will not be many years before it will be an intellectual reproach for anyone to discredit, or to be known to have discredited, this splendid and inspiring revelation.
[1a.] [1b.] Darwin: Descent of Man, 2nd edit.; London, 1874.
[2.] Huxley: Man’s Place in Nature; New York, 1883.
[3a.] [3b.] Thompson: Outlines of Zoology, 3rd edit.; Edinburgh, 1899.
[4.] Drummond: Ascent of Man; New York, 1894.
[5.] See table of geological ages, at the end of the chapter.
[6.] Haeckel: The Riddle of the Universe; New York, 1901.
[7.] Huxley: On the Origin of Species, lecture iv.
X. The Genealogy of Animals.
Life originated in the sea, and for an immense period of time after it commenced it was confined to the place of its origin. The civilisations of the earth were for many millions of years exclusively aquatic. It has, indeed, been estimated that the time required by the life process in getting out of the water—that is, that the time consumed in elaborating the first species of land animals—was much longer than the time which has elapsed since then. I presume that during a large part of this early period it would have seemed to one living at that time extremely doubtful whether there would ever be on the earth any other kinds of life than the aquatic. And if those who to-day weave the fashionable fabrics of human philosophy, and who know nothing about anything outside the thin edge of the present, had been back there, they would no doubt have declared confidently, as they looked upon the naked continents and the uninhabited air and the sea teeming with its peculiar faunas, that life upon solids or in gases, life anywhere, in fact, except in the sea, where it had always existed, and to which alone it was adapted, was absolutely, and would be forever, impossible; and that feathered fishes and fishes with the power to run and skip, and especially ‘sharks’ competent to walk on one end and jabber with the other, were unthinkable nonsense. Life originated in the sea for the same reason that the first of the series of so-called ‘civilisations’ which have appeared in human history sprang from the alluvium of the Euphrates and the Nile, because the conditions for bringing life into existence were here the most favourable. The atmosphere was incompetent to perform such a task as the inventing of protoplasm and there was no land above the oceans.
The first forms of life were one-celled—simple, jelly-like dots of almost homogeneous plasm—the protozoa. These primitive organisms were the common grandparents of all beings. From them evolved, through infinite travail and suffering, all of the orders, families, species, and varieties of animals that to-day live on the earth, and all those that have in the past lived and passed away. By the multiplication and specialisation of cells, and the formation of cell aggregates, the sponges, celenterates, and flat worms were developed from the protozoa.[1] The connecting links between the one-celled and the many-celled animals consist of a series of colonial forms of increasing size and complexity, some of which may be found in every roadside ditch and pool, while others are extinct. The development of these many-celled organisms (metazoa) from one-celled organisms was a perfectly natural process, a process which takes place in the initial evolutions of every embryo. There is no more mystery about it than there is about any other act of association. All association is simply a matter of ‘business.’ Many-celled organisms are colonies, or societies, of more or less closely co-operating one-celled organisms, and they have come into existence in obedience to the same laws of economy and advantage as have those more modern societies of metazoa known as nations, communities, and states, the organised bodies of men, ants, and millionaires.
The sponges are the lowest of the many-celled animals. They consist of irregular masses of loosely associated cells, hopelessly anchored to the sea-floor. They represent the social instinct in embryo. The cells are but slightly specialised, and each cell leads a more or less independent existence. The sponge stands at about that stage of social integration and intelligence represented by those stupendous porifera which cover continents and constitute the ‘social organisms’ of the civilised world. The nutritive system of sponges consists of countless pores opening from the surface into a common canal within, through which ever-waving cilia urge the alimental waters. In the celenterates the cells arrange themselves in the form of a cup with one large opening into and from the vase-like stomach. The unsegmented worms are flat and sac-like, with bilateral symmetry and the power to move about, but not tubular, as are the true worms. They are bloodless, like the celenterates and sponges.
From the flat worms developed the annelid worms, animals perforated by a food canal and possessing a body cavity filled with blood surrounding this canal. The body cavity is the space between the walls of the body and the alimentary canal, the cavity which in the higher animals contains the heart, liver, lungs, kidneys, etc. The worms and all animals above them have this cavity. The worms and all animals above them also have, as an inheritance from the flat worms, bodies with bilateral symmetry—that is, bodies with two halves similar. This peculiarity was probably acquired by the flat worms, and so fastened upon all subsequently evolved species, as a result of pure carelessness. It probably arose out of the habit of using continually, or over and over again, the same parts of the body as fore and aft. It has been facetiously said that if it had not been for this habit, so inadvertently acquired by these humble beings so long, long ago, we would not to-day be able to tell our right hand from our left. In the worm is found the beginning of that wonderful organ of co-ordination, the brain. The brain is a modification of the skin. It may weaken our regard for this imperial organ to know that it is, in its morphology, akin to nails and corns. But it will certainly add to our admiration for the infinite labours of evolution to remember that the magnificent thinking apparatus of modern philosophers was originally a small sensitive plate developed down in the sea a hundred million years ago on the dorsal wall of the mouths of primeval worms.
From the worms developed all of the highest four phyla of the animal kingdom—the echinoderms, the mollusks, the arthropods, and the chordate animals, the last of which were the progenitors of the illustrious vertebrates. The lowest of the mollusks are the snails, and from these humble tenants of our ponds and shores sprang the headless bivalves and the giant jawed cuttles. The mollusks were for a long time after their development the mailed monarchs of the sea, and shared with the worms the dominion of the primordial waters. But after the development of the more active arthropods, especially the crustaceans, the less agile worms and mollusks rapidly declined. Existing worms and mollusks are remnants of once powerful and populous races.
From the worms also developed the arthropods, the water-breathing crustaceans and the air-breathing spiders and insects. The crustaceans came early, away back in the gray of the Silurian period, just about the time North America was born. North America lay, a naked, V-shaped infant, in the regions of Labrador and Canada. The crustaceans rapidly superseded the mollusks as rulers of the sea, attaining, in extreme species, a length of four or five feet. The spiders and Insects came into existence toward the latter part of the Silurian period,[2] probably contemporaneous, or nearly so, with the appearance of land vegetation. The spiders and insects were the aborigines of the land and air. They are the only races of living beings, except the original inhabitants of the sea, who ever invaded and settled an unoccupied world. The earliest land fossils so far found are the fossils of scorpions. But the existence of a sting among the structural possessions of these animals indicates that there were already others who contended with them for supremacy in the new world. The first insects were the masticating insects, insects such as cockroaches, crickets, grasshoppers, dragon-flies, and beetles. They are found abundantly in the Devonian and Carboniferous rocks. The licking insects (bees) and the pricking insects (flies and bugs) appeared first in the Mesozoic Era, and the sipping insects (butterflies) in the Cenozoic. The flower-loving insects (the bees and butterflies) came into the world at the same time as did the flowers. The wings of insects may be modifications of the gills used by insect young in respiration during their aquatic existence. They are, hence, very different in origin from the wings of birds, which are the modified fore-legs of reptiles.