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

an almost forgotten “heresy.”

 

It is true that here and there a scientist of greater or less

repute—as Von Buch, Meckel, and Von Baer in Germany, Bory

Saint-Vincent in France, Wells, Grant, and Matthew in England,

and Leidy in America—had expressed more or less tentative

dissent from the doctrine of special creation and immutability of

species, but their unaggressive suggestions, usually put forward

in obscure publications, and incidentally, were utterly

overlooked and ignored. And so, despite the scientific advances

along many lines at the middle of the century, the idea of the

transmutability of organic races had no such prominence, either

in scientific or unscientific circles, as it had acquired fifty

years before. Special creation held the day, seemingly unopposed.

 

DARWIN AND THE ORIGIN OF SPECIES

 

But even at this time the fancied security of the

special-creation hypothesis was by no means real. Though it

seemed so invincible, its real position was that of an apparently

impregnable fortress beneath which, all unbeknown to the

garrison, a powder-mine has been dug and lies ready for

explosion. For already there existed in the secluded work-room of

an English naturalist, a manuscript volume and a portfolio of

notes which might have sufficed, if given publicity, to shatter

the entire structure of the special-creation hypothesis. The

naturalist who, by dint of long and patient effort, had

constructed this powder-mine of facts was Charles Robert Darwin,

grandson of the author of Zoonomia.

 

As long ago as July 1, 1837, young Darwin, then twenty-eight

years of age, had opened a private journal, in which he purposed

to record all facts that came to him which seemed to have any

bearing on the moot point of the doctrine of transmutation of

species. Four or five years earlier, during the course of that

famous trip around the world with Admiral Fitzroy, as naturalist

to the Beagle, Darwin had made the personal observations which

first tended to shake his belief of the fixity of species. In

South America, in the Pampean formation, he had discovered “great

fossil animals covered with armor like that on the existing

armadillos,” and had been struck with this similarity of type

between ancient and existing faunas of the same region. He was

also greatly impressed by the manner in which closely related

species of animals were observed to replace one another as he

proceeded southward over the continent; and “by the

South-American character of most of the productions of the

Galapagos Archipelago, and more especially by the manner in which

they differ slightly on each island of the group, none of the

islands appearing to be very ancient in a geological sense.”

 

At first the full force of these observations did not strike him;

for, under sway of Lyell’s geological conceptions, he tentatively

explained the relative absence of life on one of the Galapagos

Islands by suggesting that perhaps no species had been created

since that island arose. But gradually it dawned upon him that

such facts as he had observed “could only be explained on the

supposition that species gradually become modified.” From then

on, as he afterwards asserted, the subject haunted him; hence the

journal of 1837.

 

It will thus be seen that the idea of the variability of species

came to Charles Darwin as an inference from personal observations

in the field, not as a thought borrowed from books. He had, of

course, read the works of his grandfather much earlier in life,

but the arguments of Zoonomia and The Temple of Nature had not

served in the least to weaken his acceptance of the current

belief in fixity of species. Nor had he been more impressed with

the doctrine of Lamarck, so closely similar to that of his

grandfather. Indeed, even after his South-American experience

had aroused him to a new point of view he was still unable to see

anything of value in these earlier attempts at an explanation of

the variation of species. In opening his journal, therefore, he

had no preconceived notion of upholding the views of these or any

other makers of hypotheses, nor at the time had he formulated any

hypothesis of his own. His mind was open and receptive; he was

eager only for facts which might lead him to an understanding of

a problem which seemed utterly obscure. It was something to feel

sure that species have varied; but how have such variations been

brought about?

 

It was not long before Darwin found a clew which he thought might

lead to the answer he sought. In casting about for facts he had

soon discovered that the most available field for observation lay

among domesticated animals, whose numerous variations within

specific lines are familiar to every one. Thus under

domestication creatures so tangibly different as a mastiff and a

terrier have sprung from a common stock. So have the Shetland

pony, the thoroughbred, and the draught-horse. In short, there is

no domesticated animal that has not developed varieties deviating

more or less widely from the parent stock. Now, how has this been

accomplished? Why, clearly, by the preservation, through

selective breeding, of seemingly accidental variations. Thus one

horseman, by constantly selecting animals that “chance” to have

the right build and stamina, finally develops a race of

running-horses; while another horseman, by selecting a different

series of progenitors, has developed a race of slow, heavy

draught animals.

 

So far, so good; the preservation of “accidental” variations

through selective breeding is plainly a means by which races may

be developed that are very different from their original parent

form. But this is under man’s supervision and direction. By what

process could such selection be brought about among creatures in

a state of nature? Here surely was a puzzle, and one that must be

solved before another step could be taken in this direction.

 

The key to the solution of this puzzle came into Darwin’s mind

through a chance reading of the famous essay on “Population”

which Thomas Robert Malthus had published almost half a century

before. This essay, expositing ideas by no means exclusively

original with Malthus, emphasizes the fact that organisms tend to

increase at a geometrical ratio through successive generations,

and hence would overpopulate the earth if not somehow kept in

check. Cogitating this thought, Darwin gained a new insight into

the processes of nature. He saw that in virtue of this tendency

of each race of beings to overpopulate the earth, the entire

organic world, animal and vegetable, must be in a state of

perpetual carnage and strife, individual against individual,

fighting for sustenance and life.

 

That idea fully imagined, it becomes plain that a selective

influence is all the time at work in nature, since only a few

individuals, relatively, of each generation can come to maturity,

and these few must, naturally, be those best fitted to battle

with the particular circumstances in the midst of which they are

placed. In other words, the individuals best adapted to their

surroundings will, on the average, be those that grow to maturity

and produce offspring. To these offspring will be transmitted the

favorable peculiarities. Thus these peculiarities will become

permanent, and nature will have accomplished precisely what the

human breeder is seen to accomplish. Grant that organisms in a

state of nature vary, however slightly, one from another (which

is indubitable), and that such variations will be transmitted by

a parent to its offspring (which no one then doubted); grant,

further, that there is incessant strife among the various

organisms, so that only a small proportion can come to

maturity—grant these things, said Darwin, and we have an

explanation of the preservation of variations which leads on to

the transmutation of species themselves.

 

This wonderful coign of vantage Darwin had reached by 1839. Here

was the full outline of his theory; here were the ideas which

afterwards came to be embalmed in familiar speech in the phrases

“spontaneous variation,” and the “survival of the fittest,”

through “natural selection.” After such a discovery any ordinary

man would at once have run through the streets of science, so to

speak, screaming “Eureka!” Not so Darwin. He placed the

manuscript outline of his theory in his portfolio, and went on

gathering facts bearing on his discovery. In 1844 he made an

abstract in a manuscript book of the mass of facts by that time

accumulated. He showed it to his friend Hooker, made careful

provision for its publication in the event of his sudden death,

then stored it away in his desk and went ahead with the gathering

of more data. This was the unexploded powder-mine to which I have

just referred.

 

Twelve years more elapsed—years during which the silent worker

gathered a prodigious mass of facts, answered a multitude of

objections that arose in his own mind, vastly fortified his

theory. All this time the toiler was an invalid, never knowing a

day free from illness and discomfort, obliged to husband his

strength, never able to work more than an hour and a half at a

stretch; yet he accomplished what would have been vast

achievements for half a dozen men of robust health. Two friends

among the eminent scientists of the day knew of his labors—Sir

Joseph Hooker, the botanist, and Sir Charles Lyell, the

geologist. Gradually Hooker had come to be more than half a

convert to Darwin’s views. Lyell was still sceptical, yet he

urged Darwin to publish his theory without further delay lest he

be forestalled. At last the patient worker decided to comply with

this advice, and in 1856 he set to work to make another and

fuller abstract of the mass of data he had gathered.

 

And then a strange thing happened. After Darwin had been at work

on his “abstract” about two years, but before he had published a

line of it, there came to him one day a paper in manuscript, sent

for his approval by a naturalist friend named Alfred Russel

Wallace, who had been for some time at work in the East India

Archipelago. He read the paper, and, to his amazement, found

that it contained an outline of the same theory of “natural

selection” which he himself had originated and for twenty years

had worked upon. Working independently, on opposite sides of the

globe, Darwin and Wallace had hit upon the same explanation of

the cause of transmutation of species. “Were Wallace’s paper an

abstract of my unpublished manuscript of 1844,” said Darwin, “it

could not better express my ideas.”

 

Here was a dilemma. To publish this paper with no word from

Darwin would give Wallace priority, and wrest from Darwin the

credit of a discovery which he had made years before his

codiscoverer entered the field. Yet, on the other hand, could

Darwin honorably do otherwise than publish his friend’s paper and

himself remain silent? It was a complication well calculated to

try a man’s soul. Darwin’s was equal to the test. Keenly alive

to the delicacy of the position, he placed the whole matter

before his friends Hooker and Lyell, and left the decision as to

a course of action absolutely to them. Needless to say, these

great men did the one thing which insured full justice to all

concerned. They counselled a joint publication, to include on the

one hand Wallace’s paper, and on the other an abstract of

Darwin’s ideas, in the exact form in which it had been outlined

by the author in a letter to Asa Gray in the previous year—an

abstract which was in Gray’s hands before Wallace’s paper was in

existence. This joint production, together with a full statement

of the facts of the case, was presented to the Linnaean Society

of London by Hooker and Lyell on the evening of July 1, 1858,

this being, by an odd coincidence, the twenty-first anniversary

of the day on which Darwin had opened his journal to collect

facts bearing on the “species question.” Not often