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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.


CHAPTER 1.5. THE MODERN SCIENCE OF EVOLUTION.

We owe so much of the progress of scientific knowledge to Darwin's
Origin of Species that its influence is almost without parallel in the
history of science. The literature of Darwinism grows from day to day,
not only on the side of academic zoology and botany, the sciences
which were chiefly affected by Darwin's theory, but in a far wider
circle, so that we find Darwinism discussed in popular literature with
a vigour and zest that are given to no other scientific conception.
This remarkable success is due chiefly to two circumstances. In the
first place, all the sciences, and especially biology, have made
astounding progress in the last half-century, and have furnished a
very vast quantity of proofs of the theory of evolution. In striking
contrast to the failure of Lamarck and the older scientists to attract
attention to their effort to explain the origin of living things and
of man, we have this second and successful effort of Darwin, which was
able to gather to its support a large number of established facts.
Availing himself of the progress already made, he had very different
scientific proofs to allege than Lamarck, or St. Hilaire, or Goethe,
or Treviranus had had. But, in the second place, we must acknowledge
that Darwin had the special distinction of approaching the subject
from an entirely new side, and of basing the theory of descent on a
consistent system, which now goes by the name of Darwinism.

Lamarck had unsuccessfully attempted to explain the modification of
organisms that descend from a common form chiefly by the action of
habit and the use of organs, though with the aid of heredity. But
Darwin's success was complete when he independently sought to give a
mechanical explanation, on a quite new ground, of this modification of
plant and animal structures by adaptation and heredity. He was
impelled to his theory of selection on the following grounds. He
compared the origin of the various kinds of animals and plants which
we modify artificially - by the action of artificial selection in
horticulture and among domestic animals - with the origin of the
species of animals and plants in their natural state. He then found
that the agencies which we employ in the modification of forms by
artificial selection are also at work in Nature. The chief of these
agencies he held to be "the struggle for life." The gist of this
peculiarly Darwinian idea is given in this formula: The struggle for
existence produces new species without premeditated design in the life
of Nature, in the same way that the will of man consciously selects
new races in artificial conditions. The gardener or the farmer selects
new forms as he wills for his own profit, by ingeniously using the
agency of heredity and adaptation for the modification of structures;
so, in the natural state, the struggle for life is always
unconsciously modifying the various species of living things. This
struggle for life, or competition of organisms in securing the means
of subsistence, acts without any conscious design, but it is none the
less effective in modifying structures. As heredity and adaptation
enter into the closest reciprocal action under its influence, new
structures, or alterations of structure, are produced; and these are
purposive in the sense that they serve the organism when formed, but
they were produced without any pre-conceived aim.

This simple idea is the central thought of Darwinism, or the theory of
selection. Darwin conceived this idea at an early date, and then, for
more than twenty years, worked at the collection of empirical evidence
in support of it before he published his theory. His grandfather,
Erasmus Darwin, was an able scientist of the older school of natural
philosophy, who published a number of natural-philosophic works about
the end of the eighteenth century. The most important of them is his
Zoonomia, published in 1794, in which he expounds views similar to
those of Goethe and Lamarck, without really knowing anything of the
work of these contemporaries. However, in the writings of the
grandfather the plastic imagination rather outran the judgment, while
in Charles Darwin the two were better balanced.

Darwin did not publish any account of his theory until 1858, when
Alfred Russel Wallace, who had independently reached the same theory
of selection, published his own work. In the following year appeared
the Origin of Species, in which he develops it at length and supports
it with a mass of proof. Wallace had reached the same conclusion, but
he had not so clear a perception as Darwin of the effectiveness of
natural selection in forming species, and did not develop the theory
so fully. Nevertheless, Wallace's writings, especially those on
mimicry, etc., and an admirable work on The Geographical Distribution
of Animals, contain many fine original contributions to the theory of
selection. Unfortunately, this gifted scientist has since devoted
himself to spiritism.* (* Darwin and Wallace arrived at the theory
quite independently. Vide Wallace's Contributions to the Theory of
Natural Selection (1870) and Darwinism (1891).)

Darwin's Origin of Species had an extraordinary influence, though not
at first on the experts of the science. It took zoologists and
botanists several years to recover from the astonishment into which
they had been thrown through the revolutionary idea of the work. But
its influence on the special sciences with which we zoologists and
botanists are concerned has increased from year to year; it has
introduced a most healthy fermentation in every branch of biology,
especially in comparative anatomy and ontogeny, and in zoological and
botanical classification. In this way it has brought about almost a
revolution in the prevailing views.

However, the point which chiefly concerns us here - the extension of
the theory to man - was not touched at all in Darwin's first work in
1859. It was believed for several years that he had no thought of
applying his principles to man, but that he shared the current idea of
man holding a special position in the universe. Not only ignorant
laymen (especially several theologians), but also a number of men of
science, said very naively that Darwinism in itself was not to be
opposed; that it was quite right to use it to explain the origin of
the various species of plants and animals, but that it was totally
inapplicable to man.

In the meantime, however, it seemed to a good many thoughtful people,
laymen as well as scientists, that this was wrong; that the descent of
man from some other animal species, and immediately from some ape-like
mammal, followed logically and necessarily from Darwin's reformed
theory of evolution. Many of the acuter opponents of the theory saw at
once the justice of this position, and, as this consequence was
intolerable, they wanted to get rid of the whole theory.

The first scientific application of the Darwinian theory to man was
made by Huxley, the greatest zoologist in England. This able and
learned scientist, to whom zoology owes much of its progress,
published in 1863 a small work entitled Evidence as to Man's Place in
Nature. In the extremely important and interesting lectures which made
up this work he proved clearly that the descent of man from the ape
followed necessarily from the theory of descent. If that theory is
true, we are bound to conceive the animals which most closely resemble
man as those from which humanity has been gradually evolved. About the
same time Carl Vogt published a larger work on the same subject. We
must also mention Gustav Jaeger and Friedrich Rolle among the
zoologists who accepted and taught the theory of evolution immediately
after the publication of Darwin's book, and maintained that the
descent of man from the lower animals logically followed from it. The
latter published, in 1866, a work on the origin and position of man.

About the same time I attempted, in the second volume of my General
Morphology (1866), to apply the theory of evolution to the whole
organic kingdom, including man.* (* Huxley spoke of this "as one of
the greatest scientific works ever published." - Translator.) I
endeavoured to sketch the probable ancestral trees of the various
classes of the animal world, the protists, and the plants, as it
seemed necessary to do on Darwinian principles, and as we can actually
do now with a high degree of confidence. If the theory of descent,
which Lamarck first clearly formulated and Darwin thoroughly
established, is true, we should be able to draw up a natural
classification of plants and animals in the light of their genealogy,
and to conceive the large and small divisions of the system as the
branches and twigs of an ancestral tree. The eight genealogical tables
which I inserted in the second volume of the General Morphology are
the first sketches of their kind. In Chapter 2.27, particularly, I
trace the chief stages in man's ancestry, as far as it is possible to
follow it through the vertebrate stem. I tried especially to
determine, as well as one could at that time, the position of man in
the classification of the mammals and its genealogical significance. I
have greatly improved this attempt, and treated it in a more popular
form, in chapters 26 to 28 of my History of Creation (1868).* (* Of
which Darwin said that the Descent of Man would probably never have
been written if he had seen it earlier. - Translator.)

It was not until 1871, twelve years after the appearance of The Origin
of Species, that Darwin published the famous work which made the
much-contested application of his theory to man, and crowned the
splendid structure of his system. This important work was The Descent
of Man, and Selection in Relation to Sex. In this Darwin expressly
drew the conclusion, with rigorous logic, that man also must have been
developed out of lower species, and described the important part
played by sexual selection in the elevation of man and the other
higher animals. He showed that the careful selection which the sexes
exercise on each other in regard to sexual relations and procreation,
and the aesthetic feeling which the higher animals develop through
this, are of the utmost importance in the progressive development of
forms and the differentiation of the sexes. The males choosing the
handsomest females in one class of animals, and the females choosing
only the finest-looking males in another, the special features and the
sexual characteristics are increasingly accentuated. In fact, some of
the higher animals develop in this connection a finer taste and
judgment than man himself. But, even as regards man, it is to this
sexual selection that we owe the family-life, which is the chief
foundation of civilisation. The rise of the human race is due for the
most part to the advanced sexual selection which our ancestors
exercised in choosing their mates.

Darwin accepted in the main the general outlines of man's ancestral
tree, as I gave it in the General Morphology and the History of
Creation, and admitted that his studies led him to the same
conclusion. That he did not at once apply the theory to man in his
first work was a commendable piece of discretion; such a sequel was
bound to excite the strongest opposition to the whole theory. The
first thing to do was to establish it as regards the animal and plant
worlds. The subsequent extension to man was bound to be made sooner or
later.

It is important to understand this very clearly. If all living things
come from a common root, man must be included in the general scheme of
evolution. On the other hand, if the various species were separately
created, man, too, must have been created, and not evolved. We have to
choose between these two alternatives. This cannot be too frequently
or too strongly emphasised. EITHER all the species of animals and
plants are of supernatural origin - created, not evolved - and in that
case man also is the outcome of a creative act, as religion teaches,
OR the different species have been evolved from a few common, simple
ancestral forms, and in that case man is the highest fruit of the tree
of evolution.

We may state this briefly in the following principle - The descent of
man from the lower animals is a special deduction which inevitably
follows from the general inductive law of the whole theory of
evolution. In this principle we have a clear and plain statement of
the matter. Evolution is in reality nothing but a great induction,
which we are compelled to make by the comparative study of the most
important facts of morphology and physiology. But we must draw our
conclusion according to the laws of induction, and not attempt to
determine scientific truths by direct measurement and mathematical
calculation. In the study of living things we can scarcely ever
directly and fully, and with mathematical accuracy, determine the
nature of phenomena, as is done in the simpler study of the inorganic
world - in chemistry, physics, mineralogy, and astronomy. In the
latter, especially, we can always use the simplest and absolutely
safest method - that of mathematical determination. But in biology this
is quite impossible for various reasons; one very obvious reason being
that most of the facts of the science are very complicated and much
too intricate to allow a direct mathematical analysis. The greater
part of the phenomena that biology deals with are complicated
HISTORICAL PROCESSES, which are related to a far-reaching past, and as
a rule can only be approximately estimated. Hence we have to proceed
by INDUCTION - that is to say, to draw general conclusions, stage by
stage, and with proportionate confidence, from the accumulation of
detailed observations. These inductive conclusions cannot command
absolute confidence, like mathematical axioms; but they approach the
truth, and gain increasing probability, in proportion as we extend the
basis of observed facts on which we build. The importance of these
inductive laws is not diminished from the circumstance that they are
looked upon merely as temporary acquisitions of science, and may be
improved to any extent in the progress of scientific knowledge. The
same may be said of the attainments of many other sciences, such as
geology or archeology. However much they may be altered and improved
in detail in the course of time, these inductive truths may retain
their substance unchanged.

Now, when we say that the theory of evolution in the sense of Lamarck
and Darwin is an inductive law - in fact, the greatest of all
biological inductions - we rely, in the first place, on the facts of
paleontology. This science gives us some direct acquaintance with the
historical phenomena of the changes of species. From the situations in
which we find the fossils in the various strata of the earth we gather
confidently, in the first place, that the living population of the
earth has been gradually developed, as clearly as the earth's crust
itself; and that, in the second place, several different populations
have succeeded each other in the various geological periods. Modern
geology teaches that the formation of the earth has been gradual, and
unbroken by any violent revolutions. And when we compare together the
various kinds of animals and plants which succeed each other in the
history of our planet, we find, in the first place, a constant and
gradual increase in the number of species from the earliest times
until the present day; and, in the second place, we notice that the
forms in each great group of animals and plants also constantly
improve as the ages advance. Thus, of the vertebrates there are at
first only the lower fishes; then come the higher fishes, and later
the amphibia. Still later appear the three higher classes of
vertebrates - the reptiles, birds, and mammals, for the first time;
only the lowest and least perfect forms of the mammals are found at
first; and it is only at a very late period that placental mammals
appear, and man belongs to the latest and youngest branch of these.
Thus perfection of form increases as well as variety from the earliest
to the latest stage. That is a fact of the greatest importance. It can
only be explained by the theory of evolution, with which it is in
perfect harmony. If the different groups of plants and animals do
really descend from each other, we must expect to find this increase
in their number and perfection under the influence of natural
selection, just as the succession of fossils actually discloses it to
us.

Comparative anatomy furnishes a second series of facts which are of
great importance for the forming of our inductive law. This branch of
morphology compares the adult structures of living things, and seeks
in the great variety of organic forms the stable and simple law of
organisation, or the common type or structure. Since Cuvier founded
this science at the beginning of the nineteenth century it has been a
favourite study of the most distinguished scientists. Even before
Cuvier's time Goethe had been greatly stimulated by it, and induced to
take up the study of morphology. Comparative osteology, or the
philosophic study and comparison of the bony skeleton of the
vertebrates - one of its most interesting sections - especially
fascinated him, and led him to form the theory of the skull which I
mentioned before. Comparative anatomy shows that the internal
structure of the animals of each stem and the plants of each class is
the same in its essential features, however much they differ in
external appearance. Thus man has so great a resemblance in the chief
features of his internal organisation to the other mammals that no
comparative anatomist has ever doubted that he belongs to this class.
The whole internal structure of the human body, the arrangement of its
various systems of organs, the distribution of the bones, muscles,
blood-vessels, etc., and the whole structure of these organs in the
larger and the finer scale, agree so closely with those of the other
mammals (such as the apes, rodents, ungulates, cetacea, marsupials,
etc.) that their external differences are of no account whatever. We
learn further from comparative anatomy that the chief features of
animal structure are so similar in the various classes (fifty to sixty
in number altogether) that they may all be comprised in from eight to
twelve great groups. But even in these groups, the stem-forms or
animal types, certain organs (especially the alimentary canal) can be
proved to have been originally the same for all. We can only explain
by the theory of evolution this essential unity in internal structure
of all these animal forms that differ so much in outward appearance.
This wonderful fact can only be really understood and explained when
we regard the internal resemblance as an inheritance from common-stem
forms, and the external differences as the effect of adaptation to
different environments.

In recognising this, comparative anatomy has itself advanced to a
higher stage. Gegenbaur, the most distinguished of recent students of
this science, says that with the theory of evolution a new period
began in comparative anatomy, and that the theory in turn found a
touch stone in the science. "Up to now there is no fact in comparative
anatomy that is inconsistent with the theory of evolution; indeed,
they all lead to it. In this way the theory receives back from the
science all the service it rendered to its method." Until then
students had marvelled at the wonderful resemblance of living things



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