Our comparative investigation of the anatomy and ontogeny of the
Amphioxus and Ascidia has given us invaluable assistance. We have, in
the first place, bridged the wide gulf that has existed up to the
present between the Vertebrates and Invertebrates; and, in the second
place, we have discovered in the embryology of the Amphioxus a number
of ancient evolutionary stages that have long since disappeared from
human embryology, and have been lost, in virtue of the law of
curtailed heredity. The chief of these stages are the spherical
blastula (in its simplest primary form), and the succeeding
archigastrula, the pure, original form of the gastrula which the
Amphioxus has preserved to this day, and which we find in the same
form in a number of Invertebrates of various classes. Not less
important are the later embryonic forms of the coelomula, the
chordula, etc.
Thus the embryology of the Amphioxus and the Ascidia has so much
increased our knowledge of man's stem-history that, although our
empirical information is still very incomplete, there is now no defect
of any great consequence in it. We may now, therefore, approach our
proper task, and reconstruct the phylogeny of man in its chief lines
with the aid of this evidence of comparative anatomy and ontogeny. In
this the reader will soon see the immense importance of the direct
application of the biogenetic law. But before we enter upon the work
it will be useful to make a few general observations that are
necessary to understand the processes aright.
We must say a few words with regard to the period in which the human
race was evolved from the animal kingdom. The first thought that
occurs to one in this connection is the vast difference between the
duration of man's ontogeny and phylogeny. The individual man needs
only nine months for his complete development, from the fecundation of
the ovum to the moment when he leaves the maternal womb. The human
embryo runs its whole course in the brief space of forty weeks (as a
rule, 280 days). In many other mammals the time of the embryonic
development is much the same as in man--for instance, in the cow. In
the horse and ass it takes a little longer, forty-three to forty-five
weeks; in the camel, thirteen months. In the largest mammals, the
embryo needs a much longer period for its development in the womb--a
year and a half in the rhinoceros, and ninety weeks in the elephant.
In these cases pregnancy lasts twice as long as in the case of man, or
one and three-quarter years. In the smaller mammals the embryonic
period is much shorter. The smallest mammals, the dwarf-mice, develop
in three weeks; hares in four weeks, rats and marmots in five weeks,
the dog in nine, the pig in seventeen, the sheep in twenty-one and the
goat in thirty-six. Birds develop still more quickly. The chick only
needs, in normal circumstances, three weeks for its full development.
The duck needs twenty-five days, the turkey twenty-seven, the peacock
thirty-one, the swan forty-two, and the cassowary sixty-five. The
smallest bird, the humming-bird, leaves the egg after twelve days.
Hence the duration of individual development within the foetal
membranes is, in the mammals and birds, clearly related to the
absolute size of the body of the animal in question. But this is not
the only determining feature. There are a number of other
circumstances that have an influence on the period of embryonic
development. In the Amphioxus the earliest and most important
embryonic processes take place so rapidly that the blastula is formed
in four hours, the gastrula in six, and the typical vertebrate form in
twenty-four.
In every case the duration of ontogeny shrinks into insignificance
when we compare it with the enormous period that has been necessary
for phylogeny, or the gradual development of the ancestral series.
This period is not measured by years or centuries, but by thousands
and millions of years. Many millions of years had to pass before the
most advanced vertebrate, man, was evolved, step by step, from his
ancient unicellular ancestors. The opponents of evolution, who declare
that this gradual development of the human form from lower animal
forms, and ultimately from a unicellular organism, is an incredible
miracle, forget that the same miracle takes place within the space of
mine months in the embryonic development of every human being. Each of
us has, in the forty weeks--properly speaking, in the first four
weeks--of his development in the womb, passed through the same series
of transformations that our animal ancestors underwent in the course
of millions of years.
It is impossible to determine even approximately, in hundreds or even
thousands of years, the real and absolute duration of the phylogenetic
period. But for some time now we have, through the research of
geologists, been in a position to assign the relative length of the
various sections of the organic history of the earth. The immediate
data for determining this relative length of the geological periods
are found in the thickness of the sedimentary strata--the strata that
have been formed at the bottom of the sea or in fresh water from the
mud or slime deposited there. These successive layers of limestone,
sandstone, slate, marl, etc., which make up the greater part of the
rocks, and are often several thousand feet thick, give us a standard
for computing the relative length of the various periods.
To make the point quite clear, I must say a word about the evolution
of the earth in general, and point out briefly the chief features of
the story. In the first place, we encounter the principle that on our
planet organic life began to exist at a definite period. That
statement is no longer disputed by any competent geologist or
biologist. The organic history of the earth could not commence until
it was possible for water to settle on our planet in fluid condition.
Every organism, without exception, needs fluid water as a condition of
existence, and contains a considerable quantity of it. Our own body,
when fully formed, contains sixty to seventy per cent of water in its
tissues, and only thirty to forty per cent of solid matter. There is
even more water in the body of the child, and still more in the
embryo. In the earlier stages of development the human foetus contains
more than ninety per cent of water, and not ten per cent of solids. In
the lower marine animals, especially certain medusae, the body
consists to the extent of more than ninety-nine per cent of sea-water,
and has not one per cent of solid matter. No organism can exist or
discharge its functions without water. No water, no life!
But fluid water, on which the existence of life primarily depends,
could not exist on our planet until the temperature of the surface of
the incandescent sphere had sunk to a certain point. Up to that time
it remained in the form of steam. But as soon as the first fluid water
could be condensed from the envelope of steam, it began its geological
action, and has continued down to the present day to modify the solid
crust of the earth. The final outcome of this incessant action of the
water--wearing down and dissolving the rocks in the form of rain,
hail, snow, and ice, as running stream or boiling surge--is the
formation of mud. As Huxley says in his admirable Lectures on the
Causes of Phenomena in Organic Nature, the chief document as to the
past history of our earth is mud; the question of the history of past
ages resolves itself into a question about the formation of mud.
As I have said, it is possible to form an approximate idea of the
relative age of the various strata by comparing them at different
parts of the earth's surface. Geologists have long been agreed that
there is a definite historical succession of the different strata. The
various superimposed layers correspond to successive periods in the
organic history of the earth, in which they were deposited in the form
of mud at the bottom of the sea. The mud was gradually converted into
stone. This was lifted out of the water owing to variations in the
earth's surface, and formed the mountains. As a rule, four or five
great divisions are distinguished in the organic history of the earth,
corresponding to the larger and smaller groups of the sedimentary
strata. The larger periods are then sub-divided into a series of
smaller ones, which usually number from twelve to fifteen. The
comparative thickness of the groups of strata enables us to make an
approximate calculation of the relative length of these various
periods of time. We cannot say, it is true, "In a century a stratum of
a certain thickness (about two feet) is formed on the average;
therefore, a layer 1000 feet thick must be 500,000 years old."
Different strata of the same thickness may need very different periods
for their formation. But from the thickness or size of the stratum we
can draw some conclusion as to the RELATIVE length of the period.
The first and oldest of the four or five chief divisions of the
organic history of the earth is called the primordial, archaic, or
archeozoic period. If we compute the total average thickness of the
sedimentary strata at about 130,000 feet, this first period comprises
70,000 feet, or the greater part of the whole. For this and other
reasons we may at once conclude that the corresponding primordial or
archeolithic period must have been in itself much longer than the
whole of the remaining periods together, from its close to the present
day. It was probably much longer than the figures I have quoted (7 :
6) indicate--possibly 9 : 6. Of late years the thickness of the
archaic rocks has been put at 90,000 feet.
SYNOPSIS OF THE PALEONTOLOGICAL FORMATIONS, OR THE FOSSILIFEROUS
STRATA OF THE CRUST.
COLUMN 1 : Groups (V. down to I.).
COLUMN 2 : Systems (XIV. down to I.).
COLUMN 3 : Formations (38 down to 1).
COLUMN 4 : Synonyms of Formations.
V. Anthropolithic group, or anthropozoic (quaternary) group of strata
: XIV. Recent (alluvium) : 38. Present : Upper alluvial.
V. Anthropolithic group, or anthropozoic (quaternary) group of strata
: XIV. Recent (alluvium) : 37. Recent : Lower alluvial.
V. Anthropolithic group, or anthropozoic (quaternary) group of strata
: XIII. Pleistocene (diluvium) : 36. Post-glacial : Upper diluvial.
V. Anthropolithic group, or anthropozoic (quaternary) group of strata
: XIII. Pleistocene (diluvium) : 35. Glacial : Lower diluvial.
IV. Cenolithic group, or cenozoic (tertiary) group of strata : XII.
Pliocene (neo-tertiary) : 34. Arverne : Upper pliocene.
IV. Cenolithic group, or cenozoic (tertiary) group of strata : XII.
Pliocene (neo-tertiary) : 33. Subapennine : Lower pliocene.
IV. Cenolithic group, or cenozoic (tertiary) group of strata : XI.
Miocene (middle tertiary) : 32. Falun : Upper miocene.
IV. Cenolithic group, or cenozoic (tertiary) group of strata : XI.
Miocene (middle tertiary) : 31. Limbourg : Lower miocene.
IV. Cenolithic group, or cenozoic (tertiary) group of strata : Xb.
Oligocene (old tertiary) : 30. Aquitaine : Upper oligocene.
IV. Cenolithic group, or cenozoic (tertiary) group of strata : Xb.
Oligocene (old tertiary) : 29. Ligurium : Lower oligocene.
IV. Cenolithic group, or cenozoic (tertiary) group of strata : Xa.
Eocene (primitive tertiary) : 28. Gypsum : Upper eocene.
IV. Cenolithic group, or cenozoic (tertiary) group of strata : Xa.
Eocene (primitive tertiary) : 27. Coarse chalk : Middle eocene.
IV. Cenolithic group, or cenozoic (tertiary) group of strata : Xa.
Eocene (primitive tertiary) : 26. London clay : Lower eocene.
III. Mesolithic group, or mesozoic (secondary) group of strata : IX.
Chalk (cretaceous) : 25. White chalk. : Upper cretaceous.
III. Mesolithic group, or mesozoic (secondary) group of strata : IX.
Chalk (cretaceous) : 24. Green Sand : Middle cretaceous.
III. Mesolithic group, or mesozoic (secondary) group of strata : IX.
Chalk (cretaceous) : 23. Neocomian : Lower cretaceous.
III. Mesolithic group, or mesozoic (secondary) group of strata : IX.
Chalk (cretaceous) : 22. Wealden : Weald-formation.
III. Mesolithic group, or mesozoic (secondary) group of strata : VIII.
Jurassic : 21. Portland : Upper oolithic.
III. Mesolithic group, or mesozoic (secondary) group of strata : VIII.
Jurassic : 20. Oxford : Middle oolithic.
III. Mesolithic group, or mesozoic (secondary) group of strata : VIII.
Jurassic : 19. Bath : Lower oolithic.
III. Mesolithic group, or mesozoic (secondary) group of strata : VIII.
Jurassic : 18. Lias : Liassic.
III. Mesolithic group, or mesozoic (secondary) group of strata : VII.
Triassic : 17. Keuper : Upper triassic.
III. Mesolithic group, or mesozoic (secondary) group of strata : VII.
Triassic : 16. Muschelkalk : Middle triassic.
III. Mesolithic group, or mesozoic (secondary) group of strata : VII.
Triassic : 15. Bunter : Lower triassic.
II. Paleolithic group, or paleozoic (primary) group of strata : VIb.
Permian : 14. Zechstein : Upper permian.
II. Paleolithic group, or paleozoic (primary) group of strata : VIb.
Permian : 13. Neurot sand : Lower permian.
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 class 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 classes 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 Triassic, Jurassic, and Cretaceous. The thickness of the
strata that were deposited in this period, from the beginning of the
Triassic 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-class, the period is
called "the age of reptiles." But the bird-class was also evolved
during this period; they certainly originated from some division of
the lizard-like reptiles. This is proved by the embryological identity
of the birds and reptiles and their comparative anatomy, and, among
other features, from the circumstance 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 class of
the vertebrates, the mammals, made their appearance during the
mesozoic period. The earliest fossil remains of them were found in the
latest Triassic strata--lower jaws of small ungulates and marsupials.
More numerous remains are found a little later in the Jurassic, 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 class, the
mammals, began to preponderate. Hence the Tertiary period may be
called "the age of mammals." The highest section of this class, 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 quantity
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 analogy between the development
of languages and the evolution of species. The comparison is perfectly
just and very instructive. We could hardly find a better analogy 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 gods--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
classification of languages the same features as in the evolution and
classification 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 classify in zoology
and botany as stems, classes, 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 assistance 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 analogous 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 principal
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
illustrates 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 classes, 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 class 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 illustrates very well the analogous 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
class 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 assuming 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 albuminous 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 space 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 plasson, 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
assume 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 assume such creative action in
dealing with the first appearance of organic life on the earth.
This much-disputed question of "spontaneous generation" seems so
obscure, because people have associated with the term a mass of very
different, and often very absurd, ideas, and have attempted to solve
the difficulty by the crudest experiments. The real doctrine of the
spontaneous generation of life cannot possibly be refuted by
experiments. Every experiment that has a negative result only proves
that no organism has been formed out of inorganic matter in the
conditions--highly artificial conditions--we have established. On the
other hand, it would be exceedingly difficult to prove the theory by
way of experiment; and even if Monera were still formed daily by
spontaneous generation (which is quite possible), it would be very
difficult, if not impossible, to find a solid proof of it. Those who
will not admit the spontaneous generation of the first living things
in our sense must have recourse to a supernatural miracle; and this
is, as a matter of fact, the desperate resource to which our "exact"
scientists are driven, to the complete abdication of reason.
A famous English physicist, Lord Kelvin (then Sir W. Thomson),
attempted to dispense with the hypothesis of spontaneous generation by
assuming that the organic inhabitants of the earth were developed from
germs that came from the inhabitants of other planets, and that
chanced to fall on our planet on fragments of their original home, or
meteorites. This hypothesis found many supporters, among others the
distinguished German physicist, Helmholtz. However, it was refuted in
1872 by the able physicist, Friedrich Zollner, of Leipzig, in his
work, On the Nature of Comets. He showed clearly how unscientific this
hypothesis is; firstly in point of logic, and secondly in point of
scientific content. At the same time he pointed out that our
hypothesis of spontaneous generation is "a necessary condition for
understanding nature according to the law of causality."
I repeat that we must call in the aid of the hypothesis only as
regards the Monera, the structureless "organisms without organs."
Every complex organism must have been evolved from some lower
organism. We must not assume the spontaneous generation of even the
simplest cell, for this itself consists of at least two parts--the
internal, firm nuclear substance, and the external, softer cellular
substance or the protoplasm of the cell-body. These two parts must
have been formed by differentiation from the indifferent plasson of a
moneron, or a cytode. For this reason the natural history of the
Monera is of great interest; here alone can we find the means to
overcome the chief difficulties of the problem of spontaneous
generation. The actual living Monera are specimens of such organless
or structureless organisms, as they must have boon formed by
spontaneous generation at the commencement of the history of life.