A History of Science, vol 4 - Henry Smith Williams (epub e ink reader .txt) 📗

than one instance, for, although the color of the calyx is

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 DARWIN

Just 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 CUVIER

And 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