DARWIN AND WALLACE: THE THEORY OF NATURAL SELECTION
Charles Darwin was the grandson of Erasmus Darwin, who, as we have seen,
arrived independently at conclusions concerning the origin of species
very similar to those of Lamarck, and embodied his views in poems,
which, at the time of their publication, achieved a considerable
popularity. In the younger philosopher, however, imagination was always
kept in subjection by a determination to '_prove_ all things' and 'to
hold fast that which is good'; though, in other respects, there were not
wanting indications of the existence of hereditary characteristics in
the grandson.
Born at Shrewsbury and educated in the public school of that town,
Charles Darwin from the first exhibited signs of individuality in his
ideas and his tastes. The rigid classical teaching of his school did not
touch him, but, with the aid of his elder brother, he surreptitiously
started a chemical laboratory in a garden tool-house. From his earliest
infancy he was a collector, first of trifles, like seals and franks, but
later of stones, minerals and beetles.
At the outset, only the desire to possess new things animated him, then
a wish to put names to them, but, at a very early period, a passion
arose for learning all he could about them. Thus when only 9 or 10 years
of age, he had 'a desire of being able to know something about every
pebble in front of the hall-door,' and at 13 or 14, when he heard the
remark of a local naturalist, 'that the world would come to an end
before anyone would be able to explain how' a boulder (the 'bell-stone'
of local-fame) came to be brought from distant hills--the lad had such a
deep impression made on his mind, that he says in after life, 'I
_meditated_ over this wonderful stone[95].'
At the age of 16, he was sent to Edinburgh University to prepare himself
for the work of a doctor--the profession of his father and grandfather.
But here his independence of character again asserted itself. He found
most of the lectures 'intolerably dull,' so he occupied himself with
other pursuits, making many friendships among the younger naturalists
and doing a little in the way of biological research himself.
That he was not altogether destitute of ambition in the eyes of his
companions, however, is, I think, indicated by an amusing circumstance.
In the library of Charles Darwin, which is carefully preserved at
Cambridge, there is a copy of Jameson's _Manual of Mineralogy_,
published in 1821, which was evidently used by the young student in his
classwork at Edinburgh. In this a quizzical fellow-student has written
'Charles Darwin Esq., M.D., F.R.S.'--mischievously adding 'A.S.S.'! Even
for geology, the science to which in all his after life he became so
deeply devoted, young Darwin conceived the most violent aversion; and as
he listened to Jameson's Wernerian outpourings at Salisbury Crags, he
'determined never to attend to geology,' registering the terrible vow
'never as long as I lived to read a book on Geology, or in any way to
study the science[96].'
As it became evident that Charles Darwin would never make a doctor, his
father, after two years' trial, sent him to Cambridge with the object of
his qualifying for a clergyman. But at Christ's College, in that
University, he again took his own line--which was not that of
divinity--riding, shooting and beetle-hunting being his chief delights.
Nevertheless, at Cambridge as at Edinburgh, he seems to have shown an
appreciation for good and instructive society, and in Henslow, the
judicious and amiable Professor of Botany, the young fellow found such
sympathy and kindly help that he came to be distinguished as 'the man
who walks with Henslow[97].'
After achieving a 'pass degree,' Darwin went back to the University for
an extra term, and by the advice of Henslow began to 'think about' the
despised Science of Geology. He was introduced to that inspiring
teacher, Sedgwick, with whom he made a geological excursion into Wales;
but though he said he 'worked like a tiger' at geology, yet he, when he
got the chance of shooting on his uncle's estate, had to make the
confession, 'I should have thought myself mad to give up the first days
of partridge-shooting for geology or any other science[98].'
There is a sentence in one of the letters written at this time which
suggests that, even at this early period in his geological career,
Darwin had begun to experience some misgivings concerning the
catastrophic doctrines of his teachers and contemporaries. He says:--
'As yet I have only indulged in hypotheses, but they are such
powerful ones that I suppose, if they were put into action but
for one day, the world would come to an end[99].'
Was he not poking fun at other hypotheses besides his own?
Darwin's real scientific education began when, after some hesitation on
his father's part, he was allowed to accept the invitation, made to him
through his friend Henslow, to accompany, at his own expense, the
surveying ship _Beagle_ in a cruise to South America and afterwards
round the world. In the narrow quarters of the little 'ten-gun brig,'
he learned methodical habits and how best to economise space and time;
during his long expeditions on shore, rendered possible by the work of a
surveying vessel, he had ample opportunities for observing and
collecting; and, above all, the absence of the distractions from quiet
meditation, afforded by a long sea-voyage, proved in his case
invaluable. Very diligently did he work, accumulating a vast mass of
notes, with catalogues of the specimens he sent home from time to time
to Henslow. He had received no careful biological training, and Huxley
considered that the voluminous notes he made on zoological subjects were
almost useless[100]. Very different was the case, however, with his
geological notes. He had learned to use the blowpipe, and simple
microscope, as well as his hammer and clinometer; and the notes which he
made concerning his specimens, before packing them up for Cambridge,
were at the same time full, accurate and suggestive.
Darwin has recorded in his autobiography the wonderful effect produced
on his mind by the reading of the first volume of Lyell's
_Principles_--an effect very different from that anticipated by
Henslow[101]. From that moment he became the most enthusiastic of
geologists, and never fails in his letters to insist on his preference
for geology over all other branches of science. Again and again we find
him recording observations that he thinks will 'interest Mr Lyell' and
he says in another letter:--
'I am become a zealous disciple of Mr Lyell's views, as known in
his admirable book. Geologising in South America, I am tempted
to carry parts to a greater extent even than he does[102].'
Before reaching home after his voyage, the duration of which was
fortunately extended from two to five years, he had sent home letters
asking to be elected a fellow of the Geological Society; and,
immediately on his arrival, he gave up his zoological specimens to
others and devoted his main energies for ten years to the working up of
his geological notes and specimens.
It may seem strange that the grandson of Erasmus Darwin should in early
life have felt little or no interest in the question of the 'Origin of
Species,' but such was certainly the case. He tells us in his
autobiography that he had read his grandfather's _Zoonomia_ in his
youth, without its producing any effect on him, and when at Edinburgh he
says he heard his friend Robert Grant (afterwards Professor of Zoology
in University College, London) as they were walking together 'burst
forth in high admiration of Lamarck and his views on Evolution'--yet
Darwin adds 'I listened in silent astonishment, and as far as I can
judge without any effect on my mind[103].'
The reason of this indifference towards his grandfather's works is
obvious. All through his life, Darwin, like Lyell, showed a positive
distaste for all speculation or theorising that was not based on a good
foundation of facts or observations. In this respect, the attitude of
Darwin's mind was the very opposite of that of Herbert Spencer--who,
Huxley jokingly said, would regard as a 'tragedy'--'the killing of a
beautiful theory by an ugly fact.' Darwin tells us himself that, while
on his first reading of _Zoonomia_ he 'greatly admired' it--evidently on
literary grounds--yet 'on reading it a second time after an interval of
ten or fifteen years, I was much disappointed; _the proportion of
speculation being so large to the facts given_.' Huxley who knew Charles
Darwin so well in later years said of him that:--
'He abhors mere speculation as nature abhors a vacuum. He is as
greedy of cases and precedents as any constitutional lawyer, and
all the principles he lays down are capable of being brought to
the test of observation and experiment[104].'
What then, we may ask, were the facts and observations which turned
Darwin's mind towards the great problem that came to be the work of his
after life? I think it is possible from the study of his letters and
other published writings to give an answer to this very interesting
question.
In November 1832, Darwin returned to Monte Video, from a long journey in
the interior of the South American Continent, bringing with him many
zoological specimens and a great quantity of fossil bones, teeth and
scales, dug out by him with infinite toil from the red mud of the
Pampas--these fossils evidently belonging to the geological period that
immediately preceded that of the existing creation. The living animals
represented in his collection were all obviously very distinct from
those of Europe--consisting of curious sloths, anteaters, and
armadilloes--the so-called 'Edentata' of naturalists. And when young
Darwin came to examine and compare his _fossil_ bones, teeth and scales
he found that they too must have belonged to animals (megatherium,
mylodon, glyptodon, etc.) quite distinct from but of strikingly similar
structure to those now living in South America. What could be the
meaning of this wonderful analogy? If Cuvier and his fellow
Catastrophists were correct in their view that, at each 'revolution'
taking place on the earth's surface, the whole batch of plants and
animals was swept out of existence, and the world was restocked with a
'new creation,' why should the brand-new forms, at any particular
locality, have such a 'ghost-like' resemblance to those that had gone
before? It is interesting to note that, just at the same time, a similar
discovery was made with respect to Australia. In caves in that country,
a number of bones were found which, though evidently belonging to
'extinct' animals, yet must have belonged to forms resembling the
kangaroos and other 'pouched animals' (marsupials) now so distinctive of
that continent. But of this fact Darwin was not aware until after his
return to England in 1836.
Among the objects sent from home, which awaited Darwin on his return to
Monte Video, was the second volume of Lyell's _Principles_, then newly
published; this book, while rejecting Lamarckism, was crowded with facts
and observations concerning variation, hybridism, the struggle for
existence, and many other questions bearing on the great problem of the
origin of species. I think there can be no doubt that from this time
Darwin came to regard the question of species with an interest he had
never felt before.
It is of course not suggested that, at this early date, Darwin had
formed any definite ideas as to the _mode_ in which new species might
possibly arise from pre-existing ones or even that he had been converted
to a belief in evolution. Indeed in 1877 he wrote 'When I was on board
the _Beagle_ I believed in the permanence of species' yet he adds 'but
as far as I can remember _vague doubts_ occasionally flitted across my
mind.' Such 'vague doubts' could scarcely have failed to have arisen
when, as happened during all his journeys from north to south of the
South American Continent, he found the same curious correspondence
between existing and late fossil forms of life again and again
illustrated.
But towards the end of the voyage, an even stronger element of doubt as
to the immutability of species was awakened in his mind. When he came to
study the forms of life existing in the Galapagos Islands, off the west
coast of South America, he was startled by the discovery of the
following facts. Each small island had its own 'fauna' or assemblage of
animals--this being very strikingly shown in the case of the reptiles
and birds. And yet, though the _species_ were different, there was
obviously a very wonderful 'family likeness' to one another between the
forms in the several islands and between them all and the animals living
in the adjoining portion of the continent. Surely this could not be
accidental, but must indicate relationships due to descent from common
ancestors!
Charles Darwin returned to England in 1836, and at once made the
acquaintance of Lyell. He says in one place, 'I saw a great deal of
Lyell' and in another that 'I saw more of Lyell than of any other man,
both before and after my marriage.' In one of his letters he writes,
'You cannot conceive anything more thoroughly good natured than the
heart-and-soul manner in which he put himself in my place and thought
what would be best to do[105].' For two years Darwin was comparatively
free from the distressing malady which clouded so much of his after
life. And, during that time, he engaged very heartily with Lyell in
those combats at the Geological Society (of which he had become one of
the Secretaries) in which their joint views concerning the truth of
continuity or evolution in the inorganic world were defended against the
attacks of the militant catastrophists. Darwin, however, did not act on
the defensive alone, but brought forward a number of papers strongly
supporting his new friend's views.
There can be little doubt that, while thus engaged, and in constant
friendly intercourse with Lyell, Darwin must have felt--like other
earnest thinkers on geology at that day--that the principles they were
advocating of 'continuity' in the inorganic world must be equally
applicable to the organic world--and thus that the question of evolution
would acquire a new interest for him.
But it was undoubtedly the revision of the notes made on board the
_Beagle_, and the study of the specimens which had been sent home by him
from time to time, that produced the great determining influence on
Darwin's career. All through the voyage he had endeavoured, with as much
literary skill as he could command, to record with accuracy the
observations he made, and the conclusions to which, on careful
reflection, they seemed to point. And on his return to England, these
patiently written journals were revised and prepared for publication
forming that charming work _A Naturalist's Voyage. Journal of Researches
into the Natural History and Geology of the Countries visited during the
Voyage of H.M.S. 'Beagle' round the world._
As Darwin, with the specimens before him, revised his notes, and
reconsidered the impressions made on his mind, the 'vague doubts' he had
entertained, from time to time, concerning the immutability of species,
would come back to him with new force and cumulative effect. 'I then
saw,' he says, 'how many facts indicated the common descent of species,'
and further, '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.' In July
of that year, he opened his first note-book on the subject[106]--the
note-books being soon replaced by a series of portfolios, in which
extracts from the various works he read, facts obtained by
correspondence, the records of experiments and observation, and ideas
suggested by constant meditation were slowly accumulated for twenty
years. Mr Francis Darwin has published a series of extracts from the
note-book of 1837, which amply prove that by this time Charles Darwin
had become 'a convinced evolutionist[107].'
Fifteen months after this 'systematic enquiry' began, Darwin happened to
read the celebrated work of Malthus _On Population_, for amusement, and
this served as a spark falling on a long prepared train of thought. The
idea that as animals and plants multiply in geometrical progression,
while the supplies of food and space to be occupied remain nearly
constant, and that this must lead to a 'struggle for existence' of the
most desperate kind, was by no means new to Darwin, for the elder De
Candolle, Lyell and others had enlarged upon it; yet the facts with
regard to the human race, so strikingly presented by Malthus, brought
the whole question with such vividness before him that the idea of
'Natural Selection' flashed upon Darwin's mind. This hypothesis cannot
be better or more succinctly stated than in Huxley's words.
'All _species_ have been produced by the development of
_varieties_ from common stocks: by the conversion of these,
first into _permanent races_ and then into _new species_, by the
process of _natural selection_, which process is essentially
identical with that artificial selection by which man has
originated the races of domestic animals--the _struggle for
existence_ taking the place of man, and exerting, in the case of
natural selection, that selective action which he performs in
artificial selection[108].'
With characteristic caution, Darwin determined not to write down 'even
the briefest sketch' of this hypothesis, that had so suddenly presented
itself to his mind. His habit of thought was always to give the fullest
consideration and weight to any possible objection that presented itself
to his own mind or could be suggested to him by others. Though he was
satisfied as to the truth and importance of the principle of natural
selection, there is evidence that for some years he was oppressed by
difficulties, which I think would have seemed greater to him than to
anyone else. In my conversations with Darwin, in after years, it always
struck me that he attached an exaggerated importance to the merest
suggestion of a view opposed to that he was himself inclined to adopt;
indeed I sometimes almost feared to indicate a _possible_ different
point of view to his own, for fear of receiving such an answer as 'What
a very striking objection, how stupid of me not to see it before, I must
really reconsider the whole subject.'
While a divinity student at Cambridge, Darwin had been much struck with
the logical form of the works both of Euclid and of Paley. The rooms of
the latter he seems to have actually occupied at Christ's College and
the works of the great divine were so diligently studied that their deep
influence remained with him in after life[109].
I think it must have been the remembrance of the arguments of Paley on
the 'proofs of design' in Nature, that seem in after life to have
haunted Darwin so that for long he failed to recognise fully that the
principle of natural selection accounted not only for the _adaptation_
of an organism to its environment, but at the same time explains that
_divergence_, which must have taken place in species in order to give
rise to their wonderfully varied characters.
It was not till long after he came to Down in 1842, he tells us in his
autobiography, that his mind freed itself from this objection. He
says:--
'I can remember the very spot in the road, whilst in my
carriage, when to my joy the solution occurred to me,'
and he compares the relief to his mind as resembling the effect produced
by 'Columbus and his egg[110].' Some may think the 'solution' of
Columbus was itself not a very satisfactory one; and I am inclined to
regard the difficulties of which Darwin records so sudden and dramatic a
removal as more imaginary than real!
There can be no doubt that, as pointed out by the late Professor Alfred
Newton[111], there was among naturalists during the second quarter of
the nineteenth century a feeling of dissatisfaction with respect to
current ideas concerning the origin of species, accompanied in many
cases with one of expectation that a solution might soon be found.
Others, however, despairingly regarded it as 'the mystery of mysteries'
for which it was hopeless to attempt to find a key. There was, however,
one man, who simultaneously with Darwin was meditating earnestly on the
problem and who eventually reached the same goal.
Alfred Russel Wallace was born thirteen years after Darwin, and a
quarter of a century after Lyell. He did not possess the moderate income
that permits of entire devotion to scientific research--an advantage,
the importance of which in their own cases, both Lyell and Darwin were
always so ready to acknowledge. Wallace, after working for a time as a
land-surveyor and then as a teacher, at the age of 26 set off with
another naturalist, H. W. Bates, on a collecting tour in South
America--hoping by the sale of specimens to cover the expenses of
travel. Like Lyell and Darwin, he was an enthusiastic entomologist, and
had conceived the same passion for travel. He had, as we have already
seen, been deeply impressed by reading the _Principles of Geology_, and
after spending four years in South America undertook a second collecting
tour, which lasted twice that time, in the Malay Archipelago.
[Illustration: Alfred R. Wallace]
Before leaving England in 1848, Wallace had read and been impressed by
reading the _Vestiges of Creation_, and there can be no doubt that from
that period the question of evolution was always more or less distinctly
present in his mind. While in Sarawak in the wet season, he tells us, 'I
was quite alone with one Malay boy as cook, and during the evenings and
wet days I had nothing to do but to look over my books and ponder over
the problem which was rarely absent from my thoughts.' He goes on to
say that by 'combining the ideas he had derived from his books that
treated of the distribution of plants and animals with those he obtained
from the great work of Lyell' he thought 'some valuable conclusions
might be reached[112].' Thus originated the very remarkable paper, _On
the Law which has regulated the Introduction of New Species_, the main
conclusion of which was as follows: 'Every species has come into
existence coincident both in space and time with a pre-existing closely
allied species.' As Wallace has himself said, 'This clearly pointed to
some kind of evolution ... but the _how_ was still a secret.'
This essay was published in the _Annals and Magazine of Natural History_
in September 1855. It attracted much attention from Lyell and Darwin and
later from Huxley. One important result of it was that Darwin and
Wallace entered into friendly correspondence. But although Darwin in his
letters to Wallace informed him that he had been engaged for a long time
in collecting facts which bore on the question of the origin of species,
he gave no hint of the theory of natural selection he had conceived
seventeen years before--indeed his friends Lyell and Hooker appear at
that time to have been the only persons, outside his family circle, whom
he had taken into his confidence.
In the spring of 1858, Wallace was at Ternate in the island of Celebes,
where he lay sick with fever, and as his thoughts wandered to the
ever-present problem of species, there suddenly recurred to his memory
the writings of Malthus, which he had read twelve years before. Then and
there, 'in a sudden flash of insight' the idea of natural selection
presented itself to his mind, and after a few hours' thought the chief
points were written down, and within a week the matter was 'copied on
thin letter-paper' and sent to Darwin by the next post, with a letter to
the following effect[113]. Wallace stated that the idea seemed new to
himself and he asked Darwin, if he also thought it new, to show it to
Lyell, who had taken so much interest in his former paper. Little did
Wallace think, in the absence of all knowledge on his part of Darwin's
own conclusions, what stir would be made by his paper when it arrived in
England!
Wallace's essay was entitled _On the Tendency of Varieties to depart
indefinitely from the Original Type_, and it is a singularly lucid and
striking presentment, in small compass, of the theory of Natural
Selection.
Had these two men been of less noble and generous nature, the history of
science might have been dishonoured by a painful discussion on a
question of priority. Fortunately we are not called upon for anything
like a judicial investigation of rival claims; for Darwin as soon as he
read the essay saw that--as Lyell had often warned him might be the
case--he was completely forestalled in the publication of his theory.
The letter and paper arrived at a sad time for Darwin--he was at the
moment very ill, there was 'scarlet fever raging in his family, to which
an infant son had succumbed on the previous day, and a daughter was ill
with diphtheria[114].' Darwin at once wrote hurriedly to Lyell enclosing
the essay and saying:
'I never saw a more striking coincidence; if Wallace had my MS.
sketch written out in 1842, he could not have made a better
short abstract! Even his terms now stand as heads of my
chapters. Please return me the MS., which he does not say he
wishes me to publish, but I shall, of course, at once write and
offer to send to any journal. So all my originality, whatever it
may amount to, will be smashed, though my book, if it ever have
any value, will not be deteriorated, as all the labour consists
in the application of the theory. I hope you will approve of
Wallace's sketch, that I may tell him what to say[115].'
And Wallace--what was the line taken by him in the unfortunate
complication that had thus arisen? From the very first his action was
all that is generous and noble. Not only did he, from the first,
entirely acquiesce in the course taken by Lyell and Hooker, but, writing
in 1870, when the fame of Darwin's work had reached its full height, he
said:--
'I have felt all my life and I still feel, the most sincere
satisfaction that Mr Darwin had been at work long before me, and
that it was not left for me to attempt to write _The Origin of
Species_. I have long since measured my own strength and know
well that it would be quite unequal to that task. For abler men
than myself may confess, that they have not that untiring
patience in accumulating, and that wonderful skill in using,
large masses of facts of the most varied kind,--that wide and
accurate physiological knowledge,--that acuteness in devising
and skill in carrying out experiments,--and that admirable style
of composition, at once clear, persuasive and
judicial,--qualities which in their harmonious combination mark
out Mr Darwin as the man, perhaps of all men now living, best
fitted for the great work he has undertaken and
accomplished[116].'
And fifty years after the joint publication of the theory of Natural
Selection to the Linnean Society he said:
'_I_ was then (as often since) the "young man in a hurry," _he_'
(Darwin) 'the painstaking and patient student, seeking ever the
full demonstration of the truth he had discovered, rather than
to achieve immediate personal fame[117].'
And when he referred to the respective shares of Darwin and himself to
the credit of having brought forward the theory of natural selection, he
actually suggests as a fair proportion '_twenty years to one
week_'--those being the periods each had devoted to the subject[118]!
Never surely was such a noble example of personal abnegation! We admire
the generosity, though we cannot accept the estimate, for do we not know
that, for at least half the period of Darwin's patient quest, Wallace
had spent in deeply pondering upon the same great question?