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still usually green, and like the color of the leaves of the
stalk, it nevertheless often varies in one or another of its
parts—at the tips, the margins, the back, or even, the inward
side—while the outer still remains on green.
“The relationship of the corolla to the leaves of the stalk is
shown in more than one way, since on the stalks of some plants
appear leaves which are already more or less colored long before
they approach inflorescence; others are fully colored when near
inflorescence. Nature also goes over at once to the corolla,
sometimes by skipping over the organs of the calyx, and in such a
case we likewise have an opportunity to observe that leaves of
the stalk become transformed into petals. Thus on the stalk of
tulips, for instance, there sometimes appears an almost
completely developed and colored petal. Even more remarkable is
the case when such a leaf, half green and half of it belonging to
the stalk, remains attached to the latter, while another colored
part is raised with the corolla, and the leaf is thus torn in
two.
“The relationship between the petals and stamens is very close.
In some instances nature makes the transition regular—e.g.,
among the Canna and several plants of the same family. A true,
little-modified petal is drawn together on its upper margin, and
produces a pollen sac, while the rest of the petal takes the
place of the stamen. In double flowers we can observe this
transition in all its stages. In several kinds of roses, within
the fully developed and colored petals there appear other ones
which are drawn together in the middle or on the side. This
drawing together is produced by a small weal, which appears as a
more or less complete pollen sac, and in the same proportion the
leaf approaches the simple form of a stamen.
“The pistil in many cases looks almost like a stamen without
anthers, and the relationship between the formation of the two is
much closer than between the other parts. In retrograde fashion
nature often produces cases where the style and stigma (Narben)
become retransformed into petals—that is, the Ranunculus
Asiaticus becomes double by transforming the stigma and style of
the fruit-receptacle into real petals, while the stamens are
often found unchanged immediately behind the corolla.
“In the seed receptacles, in spite of their formation, of their
special object, and of their method of being joined together, we
cannot fail to recognize the leaf form. Thus, for instance, the
pod would be a simple leaf folded and grown together on its
margin; the siliqua would consist of more leaves folded over
another; the compound receptacles would be explained as being
several leaves which, being united above one centre, keep their
inward parts separate and are joined on their margins. We can
convince ourselves of this by actual sight when such composite
capsules fall apart after becoming ripe, because then every part
displays an opened pod.”[1]
The theory thus elaborated of the metamorphosis of parts was
presently given greater generality through extension to the
animal kingdom, in the doctrine which Goethe and Oken advanced
independently, that the vertebrate skull is essentially a
modified and developed vertebra. These were conceptions worthy of
a poet—impossible, indeed, for any mind that had not the poetic
faculty of correlation. But in this case the poet’s vision was
prophetic of a future view of the most prosaic science. The
doctrine of metamorphosis of parts soon came to be regarded as of
fundamental importance.
But the doctrine had implications that few of its early advocates
realized. If all the parts of a flower—sepal, petal, stamen,
pistil, with their countless deviations of contour and color—are
but modifications of the leaf, such modification implies a
marvellous differentiation and development. To assert that a
stamen is a metamorphosed leaf means, if it means anything, that
in the long sweep of time the leaf has by slow or sudden
gradations changed its character through successive generations,
until the offspring, so to speak, of a true leaf has become a
stamen. But if such a metamorphosis as this is possible—if the
seemingly wide gap between leaf and stamen may be spanned by the
modification of a line of organisms—where does the possibility
of modification of organic type find its bounds? Why may not the
modification of parts go on along devious lines until the remote
descendants of an organism are utterly unlike that organism? Why
may we not thus account for the development of various species of
beings all sprung from one parent stock? That, too, is a poet’s
dream; but is it only a dream? Goethe thought not. Out of his
studies of metamorphosis of parts there grew in his mind the
belief that the multitudinous species of plants and animals about
us have been evolved from fewer and fewer earlier parent types,
like twigs of a giant tree drawing their nurture from the same
primal root. It was a bold and revolutionary thought, and the
world regarded it as but the vagary of a poet.
ERASMUS DARWINJust at the time when this thought was taking form in Goethe’s
brain, the same idea was germinating in the mind of another
philosopher, an Englishman of international fame, Dr. Erasmus
Darwin, who, while he lived, enjoyed the widest popularity as a
poet, the rhymed couplets of his Botanic Garden being quoted
everywhere with admiration. And posterity repudiating the verse
which makes the body of the book, yet grants permanent value to
the book itself, because, forsooth, its copious explanatory
foot-notes furnish an outline of the status of almost every
department of science of the time.
But even though he lacked the highest art of the versifier,
Darwin had, beyond peradventure, the imagination of a poet
coupled with profound scientific knowledge; and it was his poetic
insight, correlating organisms seemingly diverse in structure and
imbuing the lowliest flower with a vital personality, which led
him to suspect that there are no lines of demarcation in nature.
“Can it be,” he queries, “that one form of organism has developed
from another; that different species are really but modified
descendants of one parent stock?” The alluring thought nestled
in his mind and was nurtured there, and grew in a fixed belief,
which was given fuller expression in his Zoonomia and in the
posthumous Temple of Nature.
Here is his rendering of the idea as versified in the Temple of
Nature:
“Organic life beneath the shoreless waves
Was born, and nursed in Ocean’s pearly caves;
First forms minute, unseen by spheric glass,
Move on the mud, or pierce the watery mass;
These, as successive generations bloom,
New powers acquire and larger limbs assume;
Whence countless groups of vegetation spring,
And breathing realms of fin, and feet, and wing.
“Thus the tall Oak, the giant of the wood,
Which bears Britannia’s thunders on the flood;
The Whale, unmeasured monster of the main;
The lordly lion, monarch of the plain;
The eagle, soaring in the realms of air,
Whose eye, undazzled, drinks the solar glare;
Imperious man, who rules the bestial crowd,
Of language, reason, and reflection proud,
With brow erect, who scorns this earthy sod,
And styles himself the image of his God—
Arose from rudiments of form and sense,
An embryon point or microscopic ens!”[2]
Here, clearly enough, is the idea of evolution. But in that day
there was little proof forthcoming of its validity that could
satisfy any one but a poet, and when Erasmus Darwin died, in
1802, the idea of transmutation of species was still but an
unsubstantiated dream.
It was a dream, however, which was not confined to Goethe and
Darwin. Even earlier the idea had come more or less vaguely to
another great dreamer—and worker—of Germany, Immanuel Kant, and
to several great Frenchmen, including De Maillet, Maupertuis,
Robinet, and the famous naturalist Buffon—a man who had the
imagination of a poet, though his message was couched in most
artistic prose. Not long after the middle of the eighteenth
century Buffon had put forward the idea of transmutation of
species, and he reiterated it from time to time from then on till
his death in 1788. But the time was not yet ripe for the idea of
transmutation of species to burst its bonds.
And yet this idea, in a modified or undeveloped form, had taken
strange hold upon the generation that was upon the scene at the
close of the eighteenth century. Vast numbers of hitherto unknown
species of animals had been recently discovered in previously
unexplored regions of the globe, and the wise men were sorely
puzzled to account for the disposal of all of these at the time
of the deluge. It simplified matters greatly to suppose that
many existing species had been developed since the episode of the
ark by modification of the original pairs. The remoter bearings
of such a theory were overlooked for the time, and the idea that
American animals and birds, for example, were modified
descendants of Old-World forms—the jaguar of the leopard, the
puma of the lion, and so on—became a current belief with that
class of humanity who accept almost any statement as true that
harmonizes with their prejudices without realizing its
implications.
Thus it is recorded with eclat that the discovery of the close
proximity of America at the northwest with Asia removes all
difficulties as to the origin of the Occidental faunas and
floras, since Oriental species might easily have found their way
to America on the ice, and have been modified as we find them by
“the well-known influence of climate.” And the persons who gave
expression to this idea never dreamed of its real significance.
In truth, here was the doctrine of evolution in a nutshell, and,
because its ultimate bearings were not clear, it seemed the most
natural of doctrines. But most of the persons who advanced it
would have turned from it aghast could they have realized its
import. As it was, however, only here and there a man like Buffon
reasoned far enough to inquire what might be the limits of such
assumed transmutation; and only here and there a Darwin or a
Goethe reached the conviction that there are no limits.
LAMARCK VERSUS CUVIERAnd even Goethe and Darwin had scarcely passed beyond that
tentative stage of conviction in which they held the thought of
transmutation of species as an ancillary belief not ready for
full exposition. There was one of their contemporaries, however,
who, holding the same conception, was moved to give it full
explication. This was the friend and disciple of Buffon, Jean
Baptiste de Lamarck. Possessed of the spirit of a poet and
philosopher, this great Frenchman had also the widest range of
technical knowledge, covering the entire field of animate nature.
The first half of his long life was devoted chiefly to botany, in
which he attained high distinction. Then, just at the beginning
of the nineteenth century, he turned to zoology, in particular to
the lower forms of animal life. Studying these lowly organisms,
existing and fossil, he was more and more impressed with the
gradations of form everywhere to be seen; the linking of diverse
families through intermediate ones; and in particular with the
predominance of low types of life in the earlier geological
strata. Called upon constantly to classify the various forms of
life in the course of his systematic writings, he found it more
and more difficult to draw sharp lines of demarcation, and at
last the suspicion long harbored grew into a settled conviction
that there is really no such thing as a species of organism in
nature; that “species” is a figment of the human imagination,
whereas in nature there are only individuals.
That certain sets of individuals are more like one another
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