THE GROWTH OF THE “ORIGIN OF SPECIES” (1837–58).
In dealing with this subject in his “Autobiography,” Darwin tells us
of his reflections whilst on the voyage of the _Beagle_, and here
mentions another observation which deeply impressed him in addition
to those which he again repeats, on the relation between the living
and the dead in the same area and on the productions of the Galapagos
Archipelago--viz. “the manner in which closely allied animals replace
one another in proceeding southwards over the continent” (of South
America). On the theory of separate creation the existence of such
representative species received no explanation, although it became
perfectly intelligible on the theory that a single species may be
modified into distinct, although nearly related, species in the course
of its range over a wide geographical area. Here, too, the evidence
is in favour of evolution simply, and does not point to any cause of
evolution.
He also implies that even at this time he regarded the beautiful
adaptations or contrivances of nature by which organisms are fitted
to their habits of life--“for instance, a woodpecker or a tree-frog
to climb trees, or a seed for dispersal by hooks or plumes”--as the
most striking and important phenomena of the organic world, and the
one great difficulty in the path of any naturalist who should attempt
to supply a motive force for evolution. And he regarded the previous
attempts at an explanation--the direct action of surroundings and the
will of the organism--as inadequate because they could not account for
such adaptations.
Therefore being convinced of evolution, but as yet unprovided with a
motive cause which in any way satisfied him, he began in July, 1837,
shortly after his return home from the _Beagle_, to collect all facts
which bore upon the modifications which man has induced in the animals
and plants which he has subjugated, following, as he tells us, the
example of Lyell in geology. He goes on to say in his “Autobiography”:--
“I soon perceived that selection was the key-stone of man’s
success in making useful races of animals and plants. But how
selection could be applied to organisms living in a state of
nature remained for some time a mystery to me.”
[Sidenote: COLLECTION OF NOTES.]
We see indications in the extracts from his note-book at this period
(viz. between July, 1837, and February, 1838), and before he had
arrived at the conception of Natural Selection, that he had the idea
of “laws of change” affecting species to some extent like the laws of
change which compel the individuals of every species to work out their
own development, the extinction of the one corresponding in a measure
to the death of the other. Thus he says, “It is a wonderful fact,
horse, elephant, and mastodon dying out about the same time in such
different quarters. Will Mr. Lyell say that some [same?] circumstance
killed it over a tract from Spain to South America? Never.” We know
that a few months later he would have himself accepted the view he
imputes to Lyell, and would have regarded the extinction as due to
some circumstance affecting the competition for food or some other
relationship with the organic life of the same district. It is probable
that the above quotation from his Diary was written in connection with
the conclusion of Chapter IX. of the first edition of the “Journal of
the Voyage” (pp. 211, 212); for the latter is a fuller exposition of
the same argument.[B]
“One is tempted to believe,” he says, “in such simple relations,
as variation of climate and food, or introduction of enemies,
or the increased numbers of other species, as the cause of the
succession of races. But it may be asked whether it is probable
that [“than” is an evident misprint in the original] any such
cause should have been in action during the same epoch over
the whole northern hemisphere, so as to destroy the _Elephas
primigenius_ on the shores of Spain, on the plains of Siberia,
and in Northern America.... These cases of extinction forcibly
recall the idea (I do not wish to draw any close analogy) of
certain fruit-trees, which, it has been asserted, though grafted
on young stems, planted in varied situations, and fertilized by
the richest manures, yet at one period have all withered away and
perished. A fixed and determined length of life has in such cases
been given to thousands and thousands of buds (or individual
germs), although produced in long succession.”
He then concludes that the animals of one species, although “each
individual appears nearly independent of its kind,” may be bound
together by common laws. He ends by arguing that the adaptations
of animals confined to certain areas cannot be related to the
peculiarities of climate or country, because other animals introduced
by man are often so much more successful than the aborigines. As to the
causes of extinction, “all that at present can be said with certainty
is that, as with the individual, so with the species, the hour of life
has run its course, and is spent.”
[Sidenote: EARLY VIEWS.]
At this time he had the conception--as we see in the succeeding
extracts from his Diary--of species being so constituted that they
must give rise to other species; or, if not, that they must die out,
just as an individual dies unrepresented if it has no offspring; that
change--and evidently change in some fixed direction--or extinction, is
inevitable in the history of a species after a certain period of time.
With this view, which presented much resemblance to that of the author
of the “Vestiges,” and which seemed uppermost in his mind at this time,
there are traces of others. Thus in one extract the “wish of parents”
was thought of as a very doubtful explanation of adaptation, while in
another we meet a tolerably clear indication of natural selection, a
variety which is not well adapted being doomed to extinction, while a
favourable one is perpetuated, the death of a species being regarded as
“a consequence ... of non-adaptation of circumstances.”
It seems certain that for fifteen months after July, 1837, he was
keenly considering the various causes of evolution which were
suggested to him by the facts of nature, and that some general idea of
natural selection presented itself to him at times, although without
any of the force and importance it assumed in his mind at a later time.
In October, 1838, he read “Malthus on Population,” and as he says:--
“Being well prepared to appreciate the struggle for existence
which everywhere goes on from long-continued observation of the
habits of animals and plants, it at once struck me that under
these circumstances favourable variations would tend to be
preserved, and unfavourable ones to be destroyed. The result of
this would be the formation of new species. Here then I had a
theory by which to work.”
[Sidenote: SKETCH OF THE “ORIGIN.”]
In June, 1842, he wrote a brief account of the theory, occupying
thirty-five pages. In Lyell’s and Hooker’s introduction to the joint
paper by Darwin and Wallace in the Linnean Society’s Journal (1858) it
is stated that the first sketch was made in 1839, but Francis Darwin
shows (“Life and Letters,” 1887, Vol. II. pp. 11, 12) that in all
probability this is an error--a note of Darwin’s referring to the first
complete grasp of the theory after reading Malthus, being mistaken for
a reference to the first written account.
In 1844 the sketch was enlarged to a written essay occupying 231 pages
folio--“a surprisingly complete presentation of the argument afterwards
familiar to us in the ‘Origin of Species’” published fifteen years
later. Professor Huxley, after reading this essay, observed that “much
more weight is attached to the influence of external conditions in
producing variation, and to the inheritance of acquired habits than in
the ‘Origin,’” while Professor Newton pointed out that the remarks on
the migration of birds anticipate the views of later writers.[C]
The explanation of divergence of species during modification
(divergence of character) had not then occurred to him, and he tells us
in the “Autobiography”:--
“I can remember the very spot in the road, whilst in my carriage,
when to my joy the solution occurred to me; and this was long
after I had come to Down. The solution, as I believe, is that
the modified offspring of all dominant and increasing forms tend
to become adapted to many and highly diversified places in the
economy of nature.”
A good example of this tendency is seen in the relations of three great
vertebrate classes--mammals, birds, and fishes--to the environments for
which they are respectively fitted: earth, air, and water. Competition
is most severe between forms most nearly alike, and hence some measure
of relief from competition is afforded when certain members of each of
these classes enter the domain of one of the others. Hence, we observe
that although mammals as a whole are terrestrial, a small minority
are aërial and aquatic; although birds are aërial, a minority are
terrestrial and aquatic; although fishes are aquatic, a minority tend
to be, at any rate largely, terrestrial and aërial.
Huxley considered it “curious that so much importance should be
attached to this supplementary idea. It seems obvious that the theory
of the origin of species by natural selection necessarily involves
the divergence of the forms selected” (“Obituary,” 1888, reprinted
in “Darwiniana,” 1893; see pp. 280, 281). But Darwin showed that
divergence might be a great advantage in itself, and would then be
directly (and not merely incidentally and indirectly) encouraged and
increased by natural selection.
[Sidenote: RESOLVE TO PUBLISH.]
As soon as the 1844 sketch was finished, Darwin wrote a letter (July
5th) as his “solemn and last request” that his wife would, in the
case of his death, devote £400, or if necessary £500, in publishing
it, and would take trouble in promoting it. He suggests Lyell as the
best editor, then Edward Forbes, then Henslow (“quite the best in many
respects”), then Hooker (“would be _very_ good”), then Strickland.
After Strickland he had thought of Owen as “very good,” but added,
“I presume he would not undertake such a work.” If no editor could
be obtained, he requested that the essay should be published as it
was--stating that it was not intended for publication in its present
form. In August, 1854, he wrote on the back of the letter: “Hooker by
far best man to edit my Species volume.”
All this shows how certain he felt that he was on firm ground, and that
his theory of natural selection was of vast importance to science. This
same strong conviction appears clearly in the first edition of the
“Origin,” and is undoubtedly one of the secrets of its power to move
the minds of men. Although the author is above all others fair-minded;
although he is most keen to discover and to bring forward all opposing
evidence, and to criticise most minutely everything favourable;
nevertheless, looking at the evidence as a whole, he has no doubt as
to its bearing, and feels, and shows that he feels, a magnificent
confidence in the truth and the importance of his theory.