If no other record of Darwin's twenty-two years (1837-59) of life and
thought after his return to England remained than the papers and books
he published during that period, we should find enough to place him on a
level with the most gifted biologists and geologists of his age. But all
that time he was occupied with thoughts, researches, and experiments, of
which the world at large perceived no fruits. Few persons suspected that
a tremendous revolution in scientific thought was in preparation at the
quiet country home at Down. New species of animals and plants were being
described by naturalists at an alarming rate. The bulk of knowledge of
specific characters and the necessity of specialisation bade fair to
make every species-monger a dry and narrow pedant; and the pedants
quarrelled about the characters and limits of their species.
In the later years of this period some rays of improvement shone out. To
end the reign of Owen's misleading types and imaginary archetypes, there
arose a wielder of two potent words, "morphology" and "biology," the
sciences of form and of life, who showed that differences of adult form
grew out of likeness and simplicity in the young; and that the life of
plants and animals was one science, their study one discipline. What
Huxley had begun to proclaim from the housetop, Darwin was meditating in
secret; and much more. Let us see how he states the case in the famous
modest opening of the "Origin of Species" (1859): "When on board H.M.S.
_Beagle_, as naturalist, I was much struck with certain facts in the
distribution of the inhabitants of South America, and in the geological
relations of the present to the past inhabitants of that continent.
These facts seemed to me to throw some light on the origin of
species--that mystery of mysteries, as it has been called by one of our
greatest philosophers. On my return home, it occurred to me, in 1837,
that something might perhaps be made out on this question by patiently
accumulating and reflecting on all sorts of facts which could possibly
have any bearing on it. After five years' work I allowed myself to
speculate on the subject, and drew up some short notes; these I enlarged
in 1844 into a sketch of the conclusions, which then seemed to me
probable: from that period to the present day I have steadily pursued
the same object. I hope that I may be excused for entering on these
personal details, as I give them to show that I have not been hasty in
coming to a decision." We learn also, independently, from the
"Expression of the Emotions" (p. 19), that Darwin as early as 1838 was
inclined to believe in the principle of evolution, or the derivation of
species from other and lower forms.
It is somewhat difficult to decide precisely what Darwin owed to his
predecessors who believed in the mutability of species and doubted their
separate creation; this is partly owing to his exceeding modesty. He
was over-ready to acknowledge the value to himself of other people's
ideas, and he under-estimated the strength of the illumination which his
own mind threw upon those ideas, transforming them from guesses into
probable hypotheses, confirming them by his vast and varied knowledge,
and building a superstructure where they had laid but an uncertain
foundation. The question was in the air; guessing replies of great
interest were made by a few who doubted the received belief; but they
were not satisfying answers and they did not effect a revolution. Goethe
in Germany, Erasmus Darwin in England,[6] and Geoffroy Saint Hilaire in
France, came independently to similar conclusions as to the mutability
of species; and Lamarck followed with several well-known works in
1801-15, in which he upholds the doctrine that all species, including
man, are descended from other species. As Darwin says, Lamarck first did
the eminent service of arousing attention to the probability of all
change in the organic, as well as in the inorganic world, being the
result of law, and not of miraculous interposition. He saw the
difficulty of distinguishing between species and varieties, the almost
perfect gradation of form in some groups, and the great similarity of
domestic breeds of animals to such species. He believed that some degree
of change was produced by the physical conditions of life, the
intercrossing of species, and by habits causing increased use or disuse
of parts. Indeed he thought very many remarkable adaptations, such as
that of the neck of the giraffe for browsing on trees, were the effect
of habit. But he attributed, perhaps, more to a law of progressive
development impressed on all forms of life, which thus would all in
time gradually cease to be lowly, their place being taken by new forms
continually or "spontaneously" generated.
It does not appear that Lamarck would by any means have sufficed to
convince Darwin, judging from his references to him in his Journal and
the "Origin." Here is the passage in which in the second edition of his
Journal he refers to the blindness of the Brazilian Tucutuco, or
Ctenomys, a rodent or gnawing mammal with the habits of a mole:
"Considering the strictly subterranean habits of the Tucutuco, the
blindness, though so common, cannot be a very serious evil; yet it
appears strange that any animal should possess an organ frequently
subject to be injured. Lamarck would have been delighted with this fact
had he known it when speculating (probably with more truth than usual
with him) on the gradually _acquired_ blindness of the Aspalax, a gnawer
living underground, and of the Proteus, a reptile living in dark caverns
filled with water, in both of which animals the eye is in an almost
rudimentary state, and is covered with a tendinous membrane and skin....
In the Tucutuco, which, I believe, never comes to the surface of the
ground, the eye is rather larger (than in the mole), but often rendered
blind and useless, though without apparently causing any inconvenience
to the animal: no doubt Lamarck would have said that the Tucutuco is
now passing into the state of the Aspalax and Proteus." Many years
afterwards in the "Origin of Species" Darwin referred to the "erroneous
views and grounds of opinion of Lamarck."
No doubt some impulse to Darwin's views in this direction would be due
to his intercourse with Dr. Grant at Edinburgh, whose celebrated paper
on the fresh-water sponge concludes with a declaration of his belief
that species are descended from other species, and that they become
improved in the course of modification. But previous to the occurrences
of his voyage, we can find no stronger influence tending to make Darwin
an evolutionist, than Lyell's "Principles of Geology," which, by showing
constant and gradual change as the law of the world's history now as in
past periods, gave emphasis and point to all observations of change and
succession in the living world. Indeed, in June, 1836, before Darwin's
voyage was over, Lyell writes to Sir John Herschel: "In regard to the
origination of new species, I am very glad to find that you think
it probable that it may be carried on through the intervention of
intermediate causes. I left this rather to be inferred, not thinking it
worth while to offend a certain class of persons by embodying in words
what would only be a speculation. But the German critics have attacked
me vigorously, saying, that by the impugning of the doctrine of
spontaneous generation, and substituting nothing in its place, I have
left them nothing but the direct and miraculous intervention of the
First Cause, as often as a new species is introduced, and hence I have
overthrown my own doctrine of revolutions carried on by a regular system
of secondary causes.... When I first came to the notion, which I never
saw expressed elsewhere, though I have no doubt it had all been thought
out before, of a succession of extinction of species, and creation of
new ones going on perpetually now, and through an indefinite period of
the past, and to continue for ages to come, all in accommodation to the
changes which must continue in the inanimate and habitable earth, the
idea struck me as the grandest which I had ever conceived, so far as
regards the attributes of the Presiding Mind."
In a succeeding paragraph, Lyell very remarkably foreshadows Darwin's
"natural selection" and "struggle for existence." He speaks of a species
being rendered more prolific in order to perpetuate its existence;
"but this would perhaps make it press too hard upon other species at
other times. Now if it be an insect it may be made in one of its
transformations to resemble a dead stick, or a leaf, or a lichen, or a
stone, so as to be somewhat less easily found by its enemies; or if this
would make it too strong, an occasional variety of the species may have
this advantage conferred on it; or if this would be still too much, one
sex of a certain variety. _Probably there is scarcely a dash of colour
on the wing or body of which the choice would be quite arbitrary, or
which might not affect its duration for thousands of years._" The
significance of the last sentence is immense, and when we reflect that
this bold but cautious thinker was in constant intercourse with Darwin,
we can readily comprehend why the second edition of the Journal was so
enthusiastically dedicated to Lyell. On page 481 of the "Origin of
Species," Darwin acknowledges that the belief that species were
immutable productions was almost unavoidable, as long as the history of
the world was thought to be of short duration: which affords another
proof how profoundly Lyell's views on the long duration of the past
history of the globe, and its modification by the slow operation of
existing causes, influenced Darwin, and led him to comprehend how
species might be modified.
We see Darwin, then, possessed of the idea that species are mutable,
informed as to past and recent changes in the animal, plant, and
physical world, seeking for causes which should suffice to produce
modification of species by a continuous law. The next step in his
progress was attention to domestic animals and cultivated plants. As he
wrote in 1864 to Haeckel, one of his most brilliant followers: "In South
America three classes of facts were brought strongly before my mind.
Firstly, the manner in which closely-allied species replace species in
going southward. Secondly, the close affinity of the species inhabiting
the islands near South America to those proper to the continent. This
struck me profoundly, especially the difference of the species in the
adjoining islets in the Galapagos Archipelago. Thirdly, the relation of
the living Edentata and Rodentia to the extinct species. I shall never
forget my astonishment when I dug out a gigantic piece of armour like
that of the living armadillo.
"Having reflected much on the foregoing facts, it seemed to me probable
that allied species were descended from a common ancestor. But during
several years I could not conceive how each form could have been
modified so as to become admirably adapted to its place in nature. I
began, therefore, to study domesticated animals and cultivated
plants,[7] and after a time perceived that man's power of selecting and
breeding from certain individuals was the most powerful of all means in
the production of new races. Having attended to the habits of animals,
and their relations to the surrounding conditions, I was able to realise
the severe struggle for existence to which all organisms are subjected;
and my geological observations had allowed me to appreciate, to a
certain extent, the duration of past geological periods. With my mind
thus prepared, I fortunately happened to read Malthus's 'Essay on
Population;' and the idea of natural selection through the struggle for
existence at once occurred to me. Of all the subordinate points in the
theory, the last which I understood was the cause of the tendency in the
descendants from a common progenitor to diverge in character."[8]
Malthus taught the inevitable tendency of all animal life to increase
beyond the means of subsistence, and expounded the checks which begin to
act when population increases too rapidly. But his book had lain
unfruitful to naturalists since 1798, until Darwin read it, and with
his special knowledge evolved from it the brilliant idea of the
preservation of better-equipped races in the struggle for life, or, as
Herbert Spencer put it, the survival of the fittest. At one bound the
gloomy revelations of misery which the "Essay on Population" contained,
were exchanged for the bright view of perpetual progress and improvement
as being necessitated and brought about by the very struggle which
ensued upon the natural increase of animal and plant life. Instead of
struggle and pain, producing starvation and extinction merely, struggle
and pain were seen as the conditions of development and improvement; the
death of the lower, the life of the higher.
It is less profitable here to attempt to sketch the history of ideas of
evolution in general, because that history as now revealed by research,
and as detailed by many writers, was not the path along which Darwin
travelled. Indeed, many of these ideas were not disinterred, and
certainly were not brought to Darwin's notice till after the publication
of the "Origin of Species." True he read Robert Chambers's "Vestiges of
Creation," which, with its "powerful and brilliant style," although
displaying in its earlier editions "little accurate knowledge and a
great want of scientific caution," Darwin acknowledges to have done
excellent service in calling attention to the subject, in removing
prejudice, and in preparing the ground for the reception of analogous
views. Herbert Spencer, in his Essay on the Development Hypothesis,
first published in _The Leader_ in March, 1852, and republished in his
"Essays" (first series, 1858), argued that species have been modified
owing to change of circumstances, basing his argument upon the analogy
of domestic animals and plants, the changes which the embryos of many
species undergo, and the difficulty of distinguishing species and
varieties.
But we need not here dwell on the works of these thinkers, important as
they are to the general history of evolutionary thought, because
Darwin's speculations had taken form long before, and he could be but
slightly indebted to them. Far in advance of them he was at work
collecting and testing the facts which alone could win general support
for his views, and experimenting incessantly with the same object in
view. Lyell and Hooker were in his confidence, and in Lyell's letters we
meet with references such as the following, dated November 13, 1854:
"You probably know about this (the remarkable orchid, Catasetum), which
will figure in C. Darwin's book on 'Species,' with many other 'ugly
facts,' as Hooker, clinging like me to the orthodox faith, calls these
and other abnormal vagaries," showing at the same time how completely
Darwin was the leader, while his friends, advanced as they were, hung
back. Again (Lyell to Hooker, July 25, 1856): "Whether Darwin persuades
you and me to renounce our faith in species (when geological epochs are
considered) or not, I foresee that many will go over to the indefinite
modifiability doctrine."
Further light is thrown on the progress of ideas on species by Sir
Joseph Hooker's admirably written Introductory Essay to the "Flora Novæ
Zelandiæ," dated November, 1853, in which he discusses among other
questions, "The Limits of Species; their Dispersion and Variation."
While still adhering on the whole to the origin of species from single
parents, or from one pair, and the permanence of specific characters, he
insists that species vary more, and are more widely distributed, than is
generally admitted, and that their distribution has been brought about
by natural causes. In this essay he makes the following statements: "Mr.
Darwin not only directed my earliest studies in the subjects of the
distribution and variation of species, but has discussed with me all the
arguments, and drawn my attention to many of the facts which I have
endeavoured to illustrate in this essay. I know of no other way in which
I can acknowledge the extent of my obligation to him, than by adding
that I should never have taken up the subject in its present form but
for the advantages I have derived from his friendship and
encouragement."
Appropriately enough, it was through Lyell and Hooker that the new
theory was introduced to the public, and it was owing to them that
Darwin did not obliterate his own claims to priority, and give them over
to Alfred Russel Wallace, who had independently come to similar
conclusions. The letter, dated June 30, 1858, in which the announcement
was conveyed to the Linnean Society, deserves quotation, as being the
authoritative and accurate record of the circumstances which launched
the "Origin of Species" upon the world:
"The accompanying papers, which we have the honour of communicating
to the Linnean Society, and which all relate to the same subject,
viz., 'The Laws which affect the Production of Varieties, Races,
and Species,' contain the results of the investigations of two
indefatigable naturalists, Mr. Charles Darwin and Mr. Alfred
Wallace.
"These gentlemen having, independently and unknown to one another,
conceived the same very ingenious theory to account for the
appearance and perpetuation of varieties and of specific forms on
our planet, may both fairly claim the merit of being original
thinkers in this important line of inquiry; but neither of them
having published his views, though Mr. Darwin has been repeatedly
urged by us to do so, and both authors having now unreservedly
placed their papers in our hands, we think it would best promote
the interests of science that a selection from them should be laid
before the Linnean Society.
"Taken in the order of their dates, they consist of--
"1. Extracts from a MS. work on species, by Mr. Darwin, which was
sketched in 1839, and copied in 1844, when the copy was read by Dr.
Hooker, and its contents afterwards communicated to Sir Charles
Lyell. The first part is devoted to 'The Variation of Organic
Beings under Domestication and in their Natural State'; and the
second chapter of that part, from which we propose to read to the
Society the extracts referred to, is headed, 'On the Variation of
Organic Beings in a State of Nature; on the Natural Means of
Selection; on the Comparison of Domestic Races and true Species.'
"2. An abstract of a private letter addressed to Professor Asa
Gray, of Boston, U.S., in October, 1857, by Mr. Darwin, in which
he repeats his views, and which shows that these remained unaltered
from 1839 to 1857.
"3. An essay by Mr. Wallace, entitled 'On the Tendency of Varieties
to depart indefinitely from the Original Type.' This was written at
Ternate in February, 1858, for the perusal of his friend and
correspondent, Mr. Darwin, and sent to him with the expressed wish
that it should be forwarded to Sir Charles Lyell, if Mr. Darwin
thought it sufficiently novel and interesting. So highly did Mr.
Darwin appreciate the value of the views therein set forth, that he
proposed, in a letter to Sir Charles Lyell, to obtain Mr. Wallace's
consent to allow the essay to be published as soon as possible. Of
this step we highly approved, provided Mr. Darwin did not withhold
from the public, as he was strongly inclined to do (in favour of
Mr. Wallace) the memoir which he had himself written on the same
subject, and which, as before stated, one of us had perused in
1844, and the contents of which we had both of us been privy to for
many years. On representing this to Mr. Darwin, he gave us
permission to make what use we thought proper of his memoir, &c.;
and in adopting our present course, of presenting it to the Linnean
Society, we have explained to him that we are not solely
considering the relative claims to priority of himself and his
friend, but the interests of science generally; for we feel it to
be desirable that views founded on a wide deduction from facts, and
matured by years of reflection, should constitute at once a goal
from which others may start, and that, while the scientific world
is waiting for the appearance of Mr. Darwin's complete work, some
of the leading results of his labours, as well as those of his
able correspondent, should together be laid before the public."
In these papers, read on July 1, 1858, Darwin's share amounts to little
more than six pages, yet within this space he describes the geometrical
rate of increase of animals, the checks that occur, the effects of
changed conditions, the natural selection of the better equipped forms
resulting from the struggle for existence, and the influence of sexual
selection. Wallace insists on essentially the same view, which he calls
that of progression and continued divergence. "This progression, by
minute steps, in various directions, but always checked and balanced by
the necessary conditions, subject to which alone existence can be
preserved, may, it is believed, be followed out so as to agree with all
the phenomena presented by organised beings, their extinction and
succession in past ages, and all the extraordinary modifications of
form, instinct, and habits which they exhibit." Those who read Wallace's
original essay can best appreciate the extraordinary simplicity and
nobility of character which inclined the elder naturalist, who had so
long held the same views, to step aside in favour of the younger man,
who from different researches was led to such similar conclusions. It
may here be added that Hooker, in the Introductory Essay to the "Flora
Tasmaniæ," dated November 4, 1859, before the publication of the "Origin
of Species," but after seeing much of it in manuscript, accepted and
advocated the view that species are derivative and mutable, and
developed it as regards the geographical distribution of plants.
FOOTNOTES:
[6: It is worth while to reproduce here a few sentences from
Erasmus Darwin's "Zoonomia," showing how acutely he guessed in the
direction of evolution.
"When we revolve in our minds, first, the great changes which we see
naturally produced in animals after their nativity.... Secondly, when we
think over the great changes introduced into various animals by
artificial or accidental cultivation.... Thirdly, when we enumerate the
great changes produced in the species of animals before their
nativity.... Fourthly, when we revolve in our minds the great similarity
of structure which obtains in all the warm-blooded animals.... Fifthly,
from their first rudiment or primordium to the termination of their
lives, all animals undergo perpetual transformations, which are in part
produced by their own exertions;... and many of these acquired forms or
propensities are transmitted to their posterity.... A great want of one
part of the animal world has consisted in the desire of the exclusive
possession of the female; and these have acquired weapons to combat each
other for this purpose.... The final cause of this contest amongst the
males seems to be that the strongest and most active animal should
propagate the species, which should thence become improved. Another
great want consists in the means of procuring food, which has
diversified the forms of all species of animals.... All which seem to
have been gradually produced during many generations by the perpetual
endeavour of the creatures to supply the want of food, and to have been
delivered to their posterity with constant improvement of them for the
purpose required.... The third great want among animals is that of
security, which seems much to have diversified the forms of their bodies
and the colour of them.... The contrivances for the purposes of security
extend even to vegetables.... Would it be too bold to imagine that in
the great length of time since the earth began to exist ... all
warm-blooded animals have arisen from one living filament, which the
Great First Cause endued with animality;... possessing the faculty of
continuing to improve by its own inherent activity, and of delivering
down those improvements by generation to its posterity, world without
end!"]
[7: In this study Darwin came into communication, as early as
1839, with the Hon. and Rev. W. Herbert, afterwards Dean of Manchester,
and received from him a personal account of his experiments on hybrids.
It was Herbert who, as early as 1822, in the fourth volume of the
"Horticultural Transactions," and in his work on the Amaryllidaceæ,
1837, declared that horticultural experiments have established, beyond
the possibility of refutation, that botanical species are only "a higher
and more permanent class of varieties." He extended the same view to
animals, and believed that single species of each genus were originally
created in a highly plastic condition, and that these have produced,
chiefly by intercrossing, but also by variation, all our existing
species.]
[8: The first portion of this important letter is quoted from
the English translation of Haeckel's "History of Creation," 1876; the
second portion from O. Schmidt's "Doctrine of Descent and Darwinism,"
having been re-written by Darwin from the German text.]