two sections of the science of evolution--between the evolution of the
individual and that of his ancestors. We have formulated this
connection in the biogenetic law; the shorter evolution, that of the
individual, or ontogenesis, is a rapid and summary repetition, a
condensed recapitulation, of the larger evolution, or that of the
species. In this principle we express all the essential points
relating to the causes of evolution; and we shall seek throughout this
work to confirm this principle and lend it the support of facts. When
we look to its CAUSAL significance, perhaps it would be better to
formulate the biogenetic law thus: "The evolution of the species and
the stem (phylon) shows us, in the physiological functions of heredity
and adaptation, the conditioning causes on which the evolution of the
individual depends"; or, more briefly: "Phylogenesis is the mechanical
cause of ontogenesis."
But before we examine the great achievement by which Darwin revealed
the causes of evolution to us, we must glance at the efforts of
earlier scientists to attain this object. Our historical inquiry into
these will be even shorter than that into the work done in the field
of ontogeny. We have very few names to consider here. At the head of
them we find the great French naturalist, Jean Lamarck, who first
established evolution as a scientific theory in 1809. Even before his
time, however, the chief philosopher, Kant, and the chief poet,
Goethe, of Germany had occupied themselves with the subject. But their
efforts passed almost without recognition in the eighteenth century. A
"philosophy of nature" did not arise until the beginning of the
nineteenth century. In the whole of the time before this no one had
ventured to raise seriously the question of the origin of species,
which is the culminating point of phylogeny. On all sides it was
regarded as an insoluble enigma.
The whole science of the evolution of man and the other animals is
intimately connected with the question of the nature of species, or
with the problem of the origin of the various animals which we group
together under the name of species. Thus the definition of the species
becomes important. It is well known that this definition was given by
Linne, who, in his famous Systema Naturae (1735), was the first to
classify and name the various groups of animals and plants, and drew
up an orderly scheme of the species then known. Since that time
"species" has been the most important and indispensable idea in
descriptive natural history, in zoological and botanical
classification; although there have been endless controversies as to
its real meaning.
What, then, is this "organic species"? Linne himself appealed directly
to the Mosaic narrative; he believed that, as it is stated in Genesis,
one pair of each species of animals and plants was created in the
beginning, and that all the individuals of each species are the
descendants of these created couples. As for the hermaphrodites
(organisms that have male and female organs in one being), he thought
it sufficed to assume the creation of one sole individual, since this
would be fully competent to propagate its species. Further developing
these mystic ideas, Linne went on to borrow from Genesis the account
of the deluge and of Noah's ark as a ground for a science of the
geographical and topographical distribution of organisms. He accepted
the story that all the plants, animals, and men on the earth were
swept away in a universal deluge, except the couples preserved with
Noah in the ark, and ultimately landed on Mount Ararat. This mountain
seemed to Linne particularly suitable for the landing, as it reaches a
height of more than 16,000 feet, and thus provides in its higher zones
the several climates demanded by the various species of animals and
plants: the animals that were accustomed to a cold climate could
remain at the summit; those used to a warm climate could descend to
the foot; and those requiring a temperate climate could remain
half-way down. From this point the re-population of the earth with
animals and plants could proceed.
It was impossible to have any scientific notion of the method of
evolution in Linne's time, as one of the chief sources of information,
paleontology, was still wholly unknown. This science of the fossil
remains of extinct animals and plants is very closely bound up with
the whole question of evolution. It is impossible to explain the
origin of living organisms without appealing to it. But this science
did not rise until a much later date. The real founder of scientific
paleontology was Georges Cuvier, the most distinguished zoologist who,
after Linne, worked at the classification of the animal world, and
effected a complete revolution in systematic zoology at the beginning
of the nineteenth century. In regard to the nature of the species he
associated himself with Linne and the Mosaic story of creation, though
this was more difficult for him with his acquaintance with fossil
remains. He clearly showed that a number of quite different animal
populations have lived on the earth; and he claimed that we must
distinguish a number of stages in the history of our planet, each of
which was characterised by a special population of animals and plants.
These successive populations were, he said, quite independent of each
other, and therefore the supernatural creative act, which was demanded
as the origin of the animals and plants by the dominant creed, must
have been repeated several times. In this way a whole series of
different creative periods must have succeeded each other; and in
connection with these he had to assume that stupendous revolutions or
cataclysms--something like the legendary deluge--must have taken place
repeatedly. Cuvier was all the more interested in these catastrophes
or cataclysms as geology was just beginning to assert itself, and
great progress was being made in our knowledge of the structure and
formation of the earth's crust. The various strata of the crust were
being carefully examined, especially by the famous geologist Werner
and his school, and the fossils found in them were being classified;
and these researches also seemed to point to a variety of creative
periods. In each period the earth's crust, composed of the various
strata, seemed to be differently constituted, just like the population
of animals and plants that then lived on it. Cuvier combined this
notion with the results of his own paleontological and zoological
research; and in his effort to get a consistent view of the whole
process of the earth's history he came to form the theory which is
known as "the catastrophic theory," or the theory of terrestrial
revolutions. According to this theory, there have been a series of
mighty cataclysms on the earth, and these have suddenly destroyed the
whole animal and plant population then living on it; after each
cataclysm there was a fresh creation of living things throughout the
earth. As this creation could not be explained by natural laws, it was
necessary to appeal to an intervention on the part of the Creator.
This catastrophic theory, which Cuvier described in a special work,
was soon generally accepted, and retained its position in biology for
half a century.
However, Cuvier's theory was completely overthrown sixty years ago by
the geologists, led by Charles Lyell, the most distinguished worker in
this field of science. Lyell proved in his famous Principles of
Geology (1830) that the theory was false, in so far as it concerned
the crust of the earth; that it was totally unnecessary to bring in
supernatural agencies or general catastrophes in order to explain the
structure and formation of the mountains; and that we can explain them
by the familiar agencies which are at work to-day in altering and
reconstructing the surface of the earth. These causes are--the action
of the atmosphere and water in its various forms (snow, ice, fog,
rain, the wear of the river, and the stormy ocean), and the volcanic
action which is exerted by the molten central mass. Lyell convincingly
proved that these natural causes are quite adequate to explain every
feature in the build and formation of the crust. Hence Cuvier's theory
of cataclysms was very soon driven out of the province of geology,
though it remained for another thirty years in undisputed authority in
biology. All the zoologists and botanists who gave any thought to the
question of the origin of organisms adhered to Cuvier's erroneous idea
of revolutions and new creations.
In order to illustrate the complete stagnancy of biology from 1830 to
1859 on the question of the origin of the various species of animals
and plants, I may say, from my own experience, that during the whole
of my university studies I never heard a single word said about this
most important problem of the science. I was fortunate enough at that
time (1852 to 1857) to have the most distinguished masters for every
branch of biological science. Not one of them ever mentioned this
question of the origin of species. Not a word was ever said about the
earlier efforts to understand the formation of living things, nor
about Lamarck's Philosophie Zoologique which had made a fresh attack
on the problem in 1809. Hence it is easy to understand the enormous
opposition that Darwin encountered when he took up the question for
the first time. His views seemed to float in the air, without a single
previous effort to support them. The whole question of the formation
of living things was considered by biologists, until 1859, as
pertaining to the province of religion and transcendentalism; even in
speculative philosophy, in which the question had been approached from
various sides, no one had ventured to give it serious treatment. This
was due to the dualistic system of Immanuel Kant, who taught a natural
system of evolution as far as the inorganic world was concerned; but,
on the whole, adopted a supernaturalist system as regards the origin
of living things. He even went so far as to say: "It is quite certain
that we cannot even satisfactorily understand, much less explain, the
nature of an organism and its internal forces on purely mechanical
principles; it is so certain, indeed, that we may confidently say: 'It
is absurd for a man to imagine even that some day a Newton will arise
who will explain the origin of a single blade of grass by natural laws
not controlled by design'--such a hope is entirely forbidden us." In
these words Kant definitely adopts the dualistic and teleological
point of view for biological science.
Nevertheless, Kant deserted this point of view at times, particularly
in several remarkable passages which I have dealt with at length in my
Natural History of Creation (chapter 5), where he expresses himself in
the opposite, or monistic, sense. In fact, these passages would
justify one, as I showed, in claiming his support for the theory of
evolution. However, these monistic passages are only stray gleams of
light; as a rule, Kant adheres in biology to the obscure dualistic
ideas, according to which the forces at work in inorganic nature are
quite different from those of the organic world. This dualistic system
prevails in academic philosophy to-day--most of our philosophers still
regarding these two provinces as totally distinct. They put, on the
one side, the inorganic or "lifeless" world, in which there are at
work only mechanical laws, acting necessarily and without design; and,
on the other, the province of organic nature, in which none of the
phenomena can be properly understood, either as regards their inner
nature or their origin, except in the light of preconceived design,
carried out by final or purposive causes.
The prevalence of this unfortunate dualistic prejudice prevented the
problem of the origin of species, and the connected question of the
origin of man, from being regarded by the bulk of people as a
scientific question at all until 1859. Nevertheless, a few
distinguished students, free from the current prejudice, began, at the
commencement of the nineteenth century, to make a serious attack on
the problem. The merit of this attaches particularly to what is known
as "the older school of natural philosophy," which has been so much
misrepresented, and which included Jean Lamarck, Buffon, Geoffroy St.
Hilaire, and Blainville in France; Wolfgang Goethe, Reinhold
Treviranus, Schelling, and Lorentz Oken in Germany [and Erasmus Darwin
in England].
The gifted natural philosopher who treated this difficult question
with the greatest sagacity and comprehensiveness was Jean Lamarck. He
was born at Bazentin, in Picardy, on August 1st, 1744; he was the son
of a clergyman, and was destined for the Church. But he turned to seek
glory in the army, and eventually devoted himself to science.
His Philosophie Zoologique was the first scientific attempt to sketch
the real course of the origin of species, the first "natural history
of creation" of plants, animals, and men. But, as in the case of
Wolff's book, this remarkably able work had no influence whatever;
neither one nor the other could obtain any recognition from their
prejudiced contemporaries. No man of science was stimulated to take an
interest in the work, and to develop the germs it contained of the
most important biological truths. The most distinguished botanists and
zoologists entirely rejected it, and did not even deign to reply to
it. Cuvier, who lived and worked in the same city, has not thought fit
to devote a single syllable to this great achievement in his memoir on
progress in the sciences, in which the pettiest observations found a
place. In short, Lamarck's Philosophie Zoologique shared the fate of
Wolff's theory of development, and was for half a century ignored and
neglected. The German scientists, especially Oken and Goethe, who were
occupied with similar speculations at the same time, seem to have
known nothing about Lamarck's work. If they had known it, they would
have been greatly helped by it, and might have carried the theory of
evolution much farther than they found it possible to do.
To give an idea of the great importance of the Philosophie Zoologique,
I will briefly explain Lamarck's leading thought. He held that there
was no essential difference between living and lifeless beings. Nature
is one united and connected system of phenomena; and the forces which
fashion the lifeless bodies are the only ones at work in the kingdom
of living things. We have, therefore, to use the same method of
investigation and explanation in both provinces. Life is only a
physical phenomenon. All the plants and animals, with man at their
head, are to be explained, in structure and life, by mechanical or
efficient causes, without any appeal to final causes, just as in the
case of minerals and other inorganic bodies. This applies equally to
the origin of the various species. We must not assume any original
creation, or repeated creations (as in Cuvier's theory), to explain
this, but a natural, continuous, and necessary evolution. The whole
evolutionary process has been uninterrupted. All the different kinds
of animals and plants which we see to-day, or that have ever lived,
have descended in a natural way from earlier and different species;
all come from one common stock, or from a few common ancestors. These
remote ancestors must have been quite simple organisms of the lowest
type, arising by spontaneous generation from inorganic matter. The
succeeding species have been constantly modified by adaptation to
their varying environment (especially by use and habit), and have
transmitted their modifications to their successors by heredity.
Lamarck was the first to formulate as a scientific theory the natural
origin of living things, including man, and to push the theory to its
extreme conclusions--the rise of the earliest organisms by spontaneous
generation (or abiogenesis) and the descent of man from the nearest
related mammal, the ape. He sought to explain this last point, which
is of especial interest to us here, by the same agencies which he
found at work in the natural origin of the plant and animal species.
He considered use and habit (adaptation) on the one hand, and heredity
on the other, to be the chief of these agencies. The most important
modifications of the organs of plants and animals are due, in his
opinion, to the function of these very organs, or to the use or disuse
of them. To give a few examples, the woodpecker and the humming-bird
have got their peculiarly long tongues from the habit of extracting
their food with their tongues from deep and narrow folds or canals;
the frog has developed the web between his toes by his own swimming;
the giraffe has lengthened his neck by stretching up to the higher
branches of trees, and so on. It is quite certain that this use or
disuse of organs is a most important factor in organic development,
but it is not sufficient to explain the origin of species.
To adaptation we must add heredity as the second and not less
important agency, as Lamarck perfectly recognised. He said that the
modification of the organs in any one individual by use or disuse was
slight, but that it was increased by accumulation in passing by
heredity from generation to generation. But he missed altogether the
principle which Darwin afterwards found to be the chief factor in the
theory of transformation--namely, the principle of natural selection
in the struggle for existence. It was partly owing to his failure to
detect this supremely important element, and partly to the poor
condition of all biological science at the time, that Lamarck did not
succeed in establishing more firmly his theory of the common descent
of man and the other animals.
Independently of Lamarck, the older German school of natural
philosophy, especially Reinhold Treviranus, in his Biologie (1802),
and Lorentz Oken, in his Naturphilosophie (1809), turned its attention
to the problem of evolution about the end of the eighteenth and
beginning of the nineteenth century. I have described its work in my
History of Creation (chapter 4). Here I can only deal with the
brilliant genius whose evolutionary ideas are of special interest--the
greatest of German poets, Wolfgang Goethe. With his keen eye for the
beauties of nature, and his profound insight into its life, Goethe was
early attracted to the study of various natural sciences. It was the
favourite occupation of his leisure hours throughout life. He gave
particular and protracted attention to the theory of colours. But the
most valuable of his scientific studies are those which relate to that
"living, glorious, precious thing," the organism. He made profound
research into the science of structures or morphology (morphae =
forms). Here, with the aid of comparative anatomy, he obtained the
most brilliant results, and went far in advance of his time. I may
mention, in particular, his vertebral theory of the skull, his
discovery of the pineal gland in man, his system of the metamorphosis
of plants, etc. These morphological studies led Goethe on to research
into the formation and modification of organic structures which we
must count as the first germ of the science of evolution. He
approaches so near to the theory of descent that we must regard him,
after Lamarck, as one of its earliest founders. It is true that he
never formulated a complete scientific theory of evolution, but we
find a number of remarkable suggestions of it in his splendid
miscellaneous essays on morphology. Some of them are really among the
very basic ideas of the science of evolution. He says, for instance
(1807): "When we compare plants and animals in their most rudimentary
forms, it is almost impossible to distinguish between them. But we may
say that the plants and animals, beginning with an almost inseparable
closeness, gradually advance along two divergent lines, until the
plant at last grows in the solid, enduring tree and the animal attains
in man to the highest degree of mobility and freedom." That Goethe was
not merely speaking in a poetical, but in a literal genealogical,
sense of this close affinity of organic forms is clear from other
remarkable passages in which he treats of their variety in outward
form and unity in internal structure. He believes that every living
thing has arisen by the interaction of two opposing formative forces
or impulses. The internal or "centripetal" force, the type or "impulse
to specification," seeks to maintain the constancy of the specific
forms in the succession of generations: this is heredity. The external
or "centrifugal" force, the element of variation or "impulse to
metamorphosis," is continually modifying the species by changing their
environment: this is adaptation. In these significant conceptions
Goethe approaches very close to a recognition of the two great
mechanical factors which we now assign as the chief causes of the
formation of species.
However, in order to appreciate Goethe's views on morphology, one must
associate his decidedly monistic conception of nature with his
pantheistic philosophy. The warm and keen interest with which he
followed, in his last years, the controversies of contemporary French
scientists, and especially the struggle between Cuvier and Geoffroy
St. Hilaire (see chapter 4 of The History of Creation), is very
characteristic. It is also necessary to be familiar with his style and
general tenour of thought in order to appreciate rightly the many
allusions to evolution found in his writings. Otherwise, one is apt to
make serious errors.
He approached so close, at the end of the eighteenth century, to the
principles of the science of evolution that he may well be described
as the first forerunner of Darwin, although he did not go so far as to
formulate evolution as a scientific system, as Lamarck did.