II. Paleolithic group, or paleozoic (primary) group of strata : VIa.

Carboniferous (coal-measures) : 12. Carboniferous sandstone : Upper carboniferous.

II. Paleolithic group, or paleozoic (primary) group of strata : VIa.

Carboniferous (coal-measures) : 11. Carboniferous limestone : Lower carboniferous.

II. Paleolithic group, or paleozoic (primary) group of strata : V.

Devonian : 10. Pilton : Upper devonian.

II. Paleolithic group, or paleozoic (primary) group of strata : V.

Devonian : 9. Ilfracombe : Middle devonian.

II. Paleolithic group, or paleozoic (primary) group of strata : V.

Devonian : 8. Linton : Lower devonian.

II. Paleolithic group, or paleozoic (primary) group of strata : IV.

Silurian : 7. Ludlow : Upper silurian.

II. Paleolithic group, or paleozoic (primary) group of strata : IV.

Silurian : 6. Wenlock : Middle silurian.

II. Paleolithic group, or paleozoic (primary) group of strata : IV.

Silurian : 5. Llandeilo : Lower silurian.

I. Archeolithic group, or archeozoic (primordial) group of strata : III. Cambrian : 4. Potsdam : Upper cambrian.

I. Archeolithic group, or archeozoic (primordial) group of strata : III. Cambrian : 3. Longmynd : Lower cambrian.

I. Archeolithic group, or archeozoic (primordial) group of strata : II. Huronian : 2. Labrador : Upper laurentian.

I. Archeolithic group, or archeozoic (primordial) group of strata : I.

Laurentian : 1. Ottawa : Lower laurentian.

The primordial period falls into three subordinate sections--the Laurentian, Huronian, and Cambrian, corresponding to the three chief groups of rocks that comprise the archaic formation. The immense period during which these rocks were forming in the primitive ocean probably comprises more than 50,000,000 years. At the commencement of it the oldest and simplest organisms were formed by spontaneous generation--the Monera, with which the history of life on our planet opened. From these were first developed unicellular organisms of the simplest character, the Protophyta and Protozoa (paulotomea, amoebae, rhizopods, infusoria, and other Protists). During this period the whole of the invertebrate ancestors of the human race were evolved from the unicellular organisms. We can deduce this from the fact that we already find remains of fossilised fishes (Selachii and Ganoids) towards the close of the following Silurian period. These are much more advanced and much younger than the lowest vertebrate, the Amphioxus, and the numerous skull-less vertebrates, related to the Amphioxus, that must have lived at that time. The whole of the invertebrate ancestors of the human race must have preceded these.

The primordial age is followed by a much shorter division, the paleozoic or Primary age. It is divided into four long periods, the Silurian, Devonian, Carboniferous, and Permian. The Silurian strata are particularly interesting because they contain the first fossil traces of vertebrates--teeth and scales of Selachii (Palaeodus) in the lower, and Ganoids (Pteraspis) in the upper Silurian. During the Devonian period the "old red sandstone" was formed; during the Carboniferous period were deposited the vast coal-measures that yield us our chief combustive material; in the Permian (or the Dyas), in fine, the new red sandstone, the Zechstein (magnesian limestone), and the Kupferschiefer (marl-slate) were formed. The collective depth of these strata is put at 40,000 to 45,000 feet. In any case, the paleozoic age, taken as a whole, was much shorter than the preceding and much longer than the subsequent periods. The strata that were deposited during this primary epoch contain a large number of fossils; besides the invertebrate species there are a good many vertebrates, and the fishes preponderate. There were so many fishes, especially primitive fishes (of the shark type) and plated fishes, during the Devonian, and also during the Carboniferous and Permian periods, that we may describe the whole paleozoic period as "the age of fishes."

Among the paleozoic plated fishes or Ganoids the Crossopterygii and the Ctenodipterina (dipneusts) are of great importance.

During this period some of the fishes began to adapt themselves to living on land, and so gave rise to the cla.s.s of the amphibia. We find in the Carboniferous period fossilised remains of five-toed amphibia, the oldest terrestrial, air-breathing vertebrates. These amphibia increase in variety in the Permian epoch. Towards the close of it we find the first Amniotes, the ancestors of the three higher cla.s.ses of Vertebrates. These are lizard-like animals; the first to be discovered was the Proterosaurus, from the marl at Eisenach. The rise of the earliest Amniotes, among which must have been the common ancestor of the reptiles, birds, and mammals, is put back towards the close of the paleozoic age by the discovery of these reptile remains. The ancestors of our race during this period were at first represented by true fishes, then by dipneusts and amphibia, and finally by the earliest Amniotes, or the Protamniotes.

The third chief section of the organic history of the earth is the Mesozoic or Secondary period. This again is subdivided into three divisions Tria.s.sic, Jura.s.sic, and Cretaceous. The thickness of the strata that were deposited in this period, from the beginning of the Tria.s.sic to the end of the Cretaceous period, is altogether about 15,000 feet, or not half as much as the paleozoic deposits. During this period there was a very brisk and manifold development in all branches of the animal kingdom. There were especially a number of new and interesting forms evolved in the vertebrate stem. Bony fishes (Teleostei) make their first appearance. Reptiles are found in extraordinary variety and number; the extinct giant-serpents (dinosauria), the sea-serpents (halisauria), and the flying lizards (pterosauria) are the most remarkable and best known of these. On account of this predominance of the reptile-cla.s.s, the period is called "the age of reptiles." But the bird-cla.s.s was also evolved during this period; they certainly originated from some division of the lizard-like reptiles. This is proved by the embryological ident.i.ty of the birds and reptiles and their comparative anatomy, and, among other features, from the circ.u.mstance that in this period there were birds with teeth in their jaws and with tails like lizards (Archeopteryx, Odontornis).

Finally, the most advanced and (for us) the most important cla.s.s of the vertebrates, the mammals, made their appearance during the mesozoic period. The earliest fossil remains of them were found in the latest Tria.s.sic strata--lower jaws of small ungulates and marsupials.

More numerous remains are found a little later in the Jura.s.sic, and some in the Cretaceous. All the mammal remains that we have from this section belong to the lower promammals and marsupials; among these were most certainly the ancestors of the human race. On the other hand, we have not found a single indisputable fossil of any higher mammal (a placental) in the whole of this period. This division of the mammals, which includes man, was not developed until later, towards the close of this or in the following period.

The fourth section of the organic history of the earth, the Tertiary or Cenozoic age, was much shorter than the preceding. The strata that were deposited during this period have a collective thickness of only about 3,000 feet. It is subdivided into four sections--the Eocene, Oligocene, Miocene, and Pliocene. During these periods there was a very varied development of higher plant and animal forms; the fauna and flora of our planet approached nearer and nearer to the character that they bear to-day. In particular, the most advanced cla.s.s, the mammals, began to preponderate. Hence the Tertiary period may be called "the age of mammals." The highest section of this cla.s.s, the placentals, now made their appearance; to this group the human race belongs. The first appearance of man, or, to be more precise, the development of man from some closely-related group of apes, probably falls in either the miocene or the pliocene period, the middle or the last section of the Tertiary period. Others believe that man properly so-called--man endowed with speech--was not evolved from the non-speaking ape-man (Pithecanthropus) until the following, the anthropozoic, age.

In this fifth and last section of the organic history of the earth we have the full development and dispersion of the various races of men, and so it is called the Anthropozoic as well as the Quaternary period.

In the imperfect condition of paleontological and ethnographical science we cannot as yet give a confident answer to the question whether the evolution of the human race from some extinct ape or lemur took place at the beginning of this or towards the middle or the end of the Tertiary period. However, this much is certain: the development of civilisation falls in the anthropozoic age, and this is merely an insignificant fraction of the vast period of the whole history of life. When we remember this, it seems ridiculous to restrict the word "history" to the civilised period. If we divide into a hundred equal parts the whole period of the history of life, from the spontaneous generation of the first Monera to the present day, and if we then represent the relative duration of the five chief sections or ages, as calculated from the average thickness of the strata they contain, as percentages of this, we get something like the following relation:--

I. Archeolithic or archeozoic (primordial) age : 53 : 6.

II. Paleolithic or paleozoic (primary) age : 32 : 1.

III. Mesolithic or mesozoic (secondary) age : 11 : 5.

IV. Cenolithic or cenozoic (tertiary) age : 2 : 3

V. Anthropolithic or anthropozoic (quaternary) age : 0 : 5.

Total : 100 : 0.

In any case, the "historical period" is an insignificant quant.i.ty compared with the vast length of the preceding ages, in which there was no question of human existence on our planet. Even the important Cenozoic or Tertiary period, in which the first placentals or higher mammals appear, probably amounts to little over two per cent of the whole organic age.

Before we approach our proper task, and, with the aid of our ontogenetic acquirements and the biogenetic law, follow step by step the paleontological development of our animal ancestors, let us glance for a moment at another, and apparently quite remote, branch of science, a general consideration of which will help us in the solving of a difficult problem. I mean the science of comparative philology.

Since Darwin gave new life to biology by his theory of selection, and raised the question of evolution on all sides, it has often been pointed out that there is a remarkable a.n.a.logy between the development of languages and the evolution of species. The comparison is perfectly just and very instructive. We could hardly find a better a.n.a.logy when we are dealing with some of the difficult and obscure features of the evolution of species. In both cases we find the action of the same natural laws.

All philologists of any competence in their science now agree that all human languages have been gradually evolved from very rudimentary beginnings. The idea that speech is a gift of the G.o.ds--an idea held by distinguished authorities only fifty years ago--is now generally abandoned, and only supported by theologians and others who admit no natural development whatever. Speech has been developed simultaneously with its organs, the larynx and tongue, and with the functions of the brain. Hence it will be quite natural to find in the evolution and cla.s.sification of languages the same features as in the evolution and cla.s.sification of organic species. The various groups of languages that are distinguished in philology as primitive, fundamental, parent, and daughter languages, dialects, etc., correspond entirely in their development to the different categories which we cla.s.sify in zoology and botany as stems, cla.s.ses, orders, families, genera, species, and varieties. The relation of these groups, partly co-ordinate and partly subordinate, in the general scheme is just the same in both cases; and the evolution follows the same lines in both.

When, with the a.s.sistance of this tree, we follow the formation of the various languages that have been developed from the common root of the ancient Indo-Germanic tongue, we get a very clear idea of their phylogeny. We shall see at the same time how a.n.a.logous this is to the development of the various groups of vertebrates that have arisen from the common stem-form of the primitive vertebrate. The ancient Indo-Germanic root-language divided first into two princ.i.p.al stems--the Slavo-Germanic and the Aryo-Romanic. The Slavo-Germanic stem then branches into the ancient Germanic and the ancient Slavo-Lettic tongues; the Aryo-Romanic into the ancient Aryan and the ancient Greco-Roman. If we still follow the genealogical tree of these four Indo-Germanic tongues, we find that the ancient Germanic divides into three branches--the Scandinavian, the Gothic, and the German.

From the ancient German came the High German and Low German; to the latter belong the Frisian, Saxon, and modern Low-German dialects. The ancient Slavo-Lettic divided first into a Baltic and a Slav language.

The Baltic gave rise to the Lett, Lithuanian, and old-Prussian varieties; the Slav to the Russian and South-Slav in the south-east, and to the Polish and Czech in the west.

We find an equally prolific branching of its two chief stems when we turn to the other division of the Indo-Germanic languages. The Greco-Roman divided into the Thracian (Albano-Greek) and the Italo-Celtic. From the latter came the divergent branches of the Italic (Roman and Latin) in the south, and the Celtic in the north: from the latter have been developed all the British (ancient British, ancient Scotch, and Irish) and Gallic varieties. The ancient Aryan gave rise to the numerous Iranian and Indian languages.

This "comparative anatomy" and evolution of languages admirably ill.u.s.trates the phylogeny of species. It is clear that in structure and development the primitive languages, mother and daughter languages, and varieties, correspond exactly to the cla.s.ses, orders, genera, and species of the animal world. In both cases the "natural"

system is phylogenetic. As we have been convinced from comparative anatomy and ontogeny, and from paleontology, that all past and living vertebrates descend from a common ancestor, so the comparative study of dead and living Indo-Germanic tongues proves beyond question that they are all modifications of one primitive language. This view of their origin is now accepted by all the chief philologists who have worked in this branch and are unprejudiced.

But the point to which I desire particularly to draw the reader's attention in this comparison of the Indo-Germanic languages with the branches of the vertebrate stem is, that one must never confuse direct descendants with collateral branches, nor extinct forms with living.

This confusion is very common, and our opponents often make use of the erroneous ideas it gives rise to for the purpose of attacking evolution generally. When, for instance, we say that man descends from the ape, this from the lemur, and the lemur from the marsupial, many people imagine that we are speaking of the living species of these orders of mammals that they find stuffed in our museums. Our opponents then foist this idea on us, and say, with more astuteness than intelligence, that it is quite impossible; or they ask us, by way of physiological experiment, to turn a kangaroo into a lemur, a lemur into a gorilla, and a gorilla into a man! The demand is childish, and the idea it rests on erroneous. All these living forms have diverged more or less from the ancestral form; none of them could engender the same posterity that the stem-form really produced thousands of years ago.

It is certain that man has descended from some extinct mammal; and we should just as certainly cla.s.s this in the order of apes if we had it before us. It is equally certain that this primitive ape descended in turn from an unknown lemur, and this from an extinct marsupial. But it is just as clear that all these extinct ancestral forms can only be claimed as belonging to the living order of mammals in virtue of their essential internal structure and their resemblance in the decisive anatomic characteristics of each ORDER. In external appearance, in the characteristics of the GENUS or SPECIES, they would differ more or less, perhaps very considerably, from all living representatives of those orders. It is a universal and natural procedure in phylogenetic development that the stem-forms themselves, with their specific peculiarities, have been extinct for some time. The forms that approach nearest to them among the living species are more or less--perhaps very substantially--different from them. Hence in our phylogenetic inquiry and in the comparative study of the living, divergent descendants, there can only be a question of determining the greater or less remoteness of the latter from the ancestral form. Not a single one of the older stem-forms has continued unchanged down to our time.

We find just the same thing in comparing the various dead and living languages that have developed from a common primitive tongue. If we examine our genealogical tree of the Indo-Germanic languages in this light, we see at once that all the older or parent tongues, of which we regard the living varieties of the stem as divergent daughter or grand-daughter languages, have been extinct for some time. The Aryo-Romanic and the Slavo-Germanic tongues have completely disappeared; so also the Aryan, the Greco-Roman, the Slavo-Lettic, and the ancient Germanic. Even their daughters and grand-daughters have been lost; all the living Indo-Germanic languages are only related in the sense that they are divergent descendants of common stem-forms.

Some forms have diverged more, and some less, from the original stem-form.

This easily demonstrable fact ill.u.s.trates very well the a.n.a.logous case of the origin of the vertebrate species. Phylogenetic comparative philology here yields a strong support to phylogenetic comparative zoology. But the one can adduce more direct evidence than the other, as the paleontological material of philology--the old monuments of the extinct tongue--have been preserved much better than the paleontological material of zoology, the fossilised bones and imprints of vertebrates.

We may, however, trace man's genealogical tree not only as far as the lower mammals, but much further--to the amphibia, to the shark-like primitive fishes, and, in fine, to the skull-less vertebrates that closely resembled the Amphioxus. But this must not be understood in the sense that the existing Amphioxus, or the sharks or amphibia of to-day, can give us any idea of the external appearance of these remote stem-forms. Still less must it be thought that the Amphioxus or any actual shark, or any living species of amphibia, is a real ancestral form of the higher vertebrates and man. The statement can only rationally mean that the living forms I have referred to are COLLATERAL LINES that are much more closely related to the extinct stem-forms, and have retained the resemblance much better, than any other animals we know. They are still so like them in regard to their distinctive internal structure that we should put them in the same cla.s.s with the extinct forms if we had these before us. But no direct descendants of these earlier forms have remained unchanged. Hence we must entirely abandon the idea of finding direct ancestors of the human race in their characteristic EXTERNAL FORM among the living species of animals. The essential and distinctive features that still connect living forms more or less closely with the extinct common stem-forms lie in the internal structure, not the external appearance.

The latter has been much modified by adaptation. The former has been more or less preserved by heredity.

Comparative anatomy and ontogeny prove beyond question that man is a true vertebrate, and, therefore, man's special genealogical tree must be connected with that of the other Vertebrates, which spring from a common root with him. But we have also many important grounds in comparative anatomy and ontogeny for a.s.suming a common origin for all the Vertebrates. If the general theory of evolution is correct, all the Vertebrates, including man, come from a single common ancestor, a long-extinct "Primitive Vertebrate." Hence the genealogical tree of the Vertebrates is at the same time that of the human race.

Our task, therefore, of constructing man's genealogy becomes the larger aim of discovering the genealogy of the entire vertebrate stem.

As we now know from the comparative anatomy and ontogeny of the Amphioxus and the Ascidia, this is in turn connected with the genealogical tree of the Invertebrates (directly with that of the Vermalia), but has no direct connection with the independent stems of the Articulates, Molluscs, and Echinoderms. If we do thus follow our ancestral tree through various stages down to the lowest worms, we come inevitably to the Gastraea, that most instructive form that gives the clearest possible picture of an animal with two germinal layers.

The Gastraea itself has originated from the simple multicellular vesicle, the Blastaea, and this in turn must have been evolved from the lowest circle of unicellular animals, to which we give the name of Protozoa. We have already considered the most important primitive type of these, the unicellular Amoeba, which is extremely instructive when compared with the human ovum. With this we reach the lowest of the solid data to which we are to apply our biogenetic law, and by which we may deduce the extinct ancestor from the embryonic form. The amoeboid nature of the young ovum and the unicellular condition in which (as stem-cell or cytula) every human being begins its existence justify us in affirming that the earliest ancestors of the human race were simple amoeboid coils.

But the further question now arises: "Whence came these first amoebae with which the history of life began at the commencement of the Laurentian epoch?" There is only one answer to this. The earliest unicellular organisms can only have been evolved from the simplest organisms we know, the Monera. These are the simplest living things that we can conceive. Their whole body is nothing but a particle of plasm, a granule of living alb.u.minous matter, discharging of itself all the essential vital functions that form the material basis of life. Thus we come to the last, or, if you prefer, the first, question in connection with evolution--the question of the origin of the Monera. This is the real question of the origin of life, or of spontaneous generation.

We have neither s.p.a.ce nor occasion to go further in this Chapter into the question of spontaneous generation. For this I must refer the reader to the fifteenth chapter of the History of Creation, and especially to the second book of the General Morphology, or to the essay on "The Monera and Spontaneous Generation" in my Studies of the Monera and other Protists.* (* The English reader will find a luminous and up-to-date chapter on the subject in Haeckel's recently written and translated Wonders of Life.--Translator.) I have given there fully my own view of this important question. The famous botanist Nageli afterwards (1884) developed the same ideas. I will only say a few words here about this obscure question of the origin of life, in so far as our main subject, organic evolution in general, is affected by it. Spontaneous generation, in the definite and restricted sense in which I maintain it, and claim that it is a necessary hypothesis in explaining the origin of life, refers solely to the evolution of the Monera from inorganic carbon-compounds. When living things made their first appearance on our planet, the very complex nitrogenous compound of carbon that we call pla.s.son, which is the earliest material embodiment of vital action, must have been formed in a purely chemical way from inorganic carbon-compounds. The first Monera were formed in the sea by spontaneous generation, as crystals are formed in the mother-water. Our demand for a knowledge of causes compels us to a.s.sume this. If we believe that the whole inorganic history of the earth has proceeded on mechanical principles without any intervention of a Creator, and that the history of life also has been determined by the same mechanical laws; if we see that there is no need to admit creative action to explain the origin of the various groups of organisms; it is utterly irrational to a.s.sume such creative action in dealing with the first appearance of organic life on the earth.