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.
My work is
now nearly finished; but as
it will take me two or
three more years to complete
it, and as my health is far from
strong, I have been urged to
publish this Abstract. I have
more especially been induced
to do this, as Mr Wallace, who
is now studying the natural history
of the Malay archipelago, has
arrived at almost exactly the
same general conclusions that
I have on the origin of species.
Last year he sent to me a memoir
on this subject, with a request
that I would forward it to Sir
Charles Lyell, who sent it to
the Linnean Society, and it is
published in the third volume
of the journal of that Society.
Sir C. Lyell and Dr Hooker, who
both knew of my work —the
latter having read my sketch
of 1844 —honoured me by
thinking it advisable to publish,
with Mr Wallace's excellent memoir,
some brief extracts from my manuscripts.
This Abstract, which I now
publish, must necessarily be
imperfect. I cannot here give
references and authorities for
my several statements; and I
must trust to the reader reposing
some confidence in my accuracy.
No doubt errors will have crept
in, though I hope I have always
been cautious in trusting to
good authorities alone. I can
here give only the general conclusions
at which I have arrived, with
a few facts in illustration,
but which, I hope, in most cases
will suffice. No one can feel
more sensible than I do of the
necessity of hereafter publishing
in detail all the facts, with
references, on which my conclusions
have been grounded; and I hope
in a future work to do this.
For I am well aware that scarcely
a single point is discussed in
this volume on which facts cannot
be adduced, often apparently
leading to conclusions directly
opposite to those at which I
have arrived. A fair result can
be obtained only by fully stating
and balancing the facts and arguments
on both sides of each question;
and this cannot possibly be here
done.
I much regret that want of
space prevents my having the
satisfaction of acknowledging
the generous assistance which
I have received from very many
naturalists, some of them personally
unknown to me. I cannot, however,
let this opportunity pass without
expressing my deep obligations
to Dr Hooker, who for the last
fifteen years has aided me in
every possible way by his large
stores of knowledge and his excellent
judgement.
In considering
the Origin of Species, it is
quite conceivable
that a naturalist, reflecting
on the mutual affinities of organic
beings, on their embryological
relations, their geographical
distribution, geological succession,
and other such facts, might come
to the conclusion that each species
had not been independently created,
but had descended, like varieties,
from other species. Nevertheless,
such a conclusion, even if well
founded, would be unsatisfactory,
until it could be shown how the
innumerable species inhabiting
this world have been modified
so as to acquire that perfection
of structure and co-adaptation
which most justly excites our
admiration. Naturalists continually
refer to external conditions,
such as climate, food, &c.,
as the only possible cause of
variation. In one very limited
sense, as we shall hereafter
see, this may be true; but it
is preposterous to attribute
to mere external conditions,
the structure, for instance,
of the woodpecker, with its feet,
tail, beak, and tongue, so admirably
adapted to catch insects under
the bark of trees. In the case
of the misseltoe, which draws
its nourishment from certain
trees, which has seeds that must
be transported by certain birds,
and which has flowers with separate
sexes absolutely requiring the
agency of certain insects to
bring pollen from one flower
to the other, it is equally preposterous
to account for the structure
of this parasite, with its relations
to several distinct organic beings,
by the effects of external conditions,
or of habit, or of the volition
of the plant itself.
The author of the 'Vestiges
of Creation' would, I presume,
say that, after a certain unknown
number of generations, some bird
had given birth to a woodpecker,
and some plant to the misseltoe,
and that these had been produced
perfect as we now see them; but
this assumption seems to me to
be no explanation, for it leaves
the case of the coadaptations
of organic beings to each other
and to their physical conditions
of life, untouched and unexplained.
It is, therefore, of the highest
importance to gain a clear insight
into the means of modification
and coadaptation. At the commencement
of my observations it seemed
to me probable that a careful
study of domesticated animals
and of cultivated plants would
offer the best chance of making
out this obscure problem. Nor
have I been disappointed; in
this and in all other perplexing
cases I have invariably found
that our knowledge, imperfect
though it be, of variation under
domestication, afforded the best
and safest clue. I may venture
to express my conviction of the
high value of such studies, although
they have been very commonly
neglected by naturalists.
From these considerations,
I shall devote the first chapter
of this Abstract to Variation
under Domestication. We shall
thus see that a large amount
of hereditary modification is
at least possible, and, what
is equally or more important,
we shall see how great is the
power of man in accumulating
by his Selection successive slight
variations. I will then pass
on to the variability of species
in a state of nature; but I shall,
unfortunately, be compelled to
treat this subject far too briefly,
as it can be treated properly
only by giving long catalogues
of facts. We shall, however,
be enabled to discuss what circumstances
are most favourable to variation.
In the next chapter the Struggle
for Existence amongst all organic
beings throughout the world,
which inevitably follows from
their high geometrical powers
of increase, will be treated
of. This is the doctrine of Malthus,
applied to the whole animal and
vegetable kingdoms. As many more
individuals of each species are
born than can possibly survive;
and as, consequently, there is
a frequently recurring struggle
for existence, it follows that
any being, if it vary however
slightly in any manner profitable
to itself, under the complex
and sometimes varying conditions
of life, will have a better chance
of surviving, and thus be naturally
selected. From the strong
principle of inheritance, any
selected variety will tend to
propagate its new and modified
form.
This fundamental subject of
Natural Selection will be treated
at some length in the fourth
chapter; and we shall then see
how Natural Selection almost
inevitably causes much Extinction
of the less improved forms of
life and induces what I have
called Divergence of Character.
In the next chapter I shall discuss
the complex and little known
laws of variation and of correlation
of growth. In the four succeeding
chapters, the most apparent and
gravest difficulties on the theory
will be given: namely, first,
the difficulties of transitions,
or understanding how a simple
being or a simple organ can be
changed and perfected into a
highly developed being or elaborately
constructed organ; secondly the
subject of Instinct, or the mental
powers of animals, thirdly, Hybridism,
or the infertility of species
and the fertility of varieties
when intercrossed; and fourthly,
the imperfection of the Geological
Record. In the next chapter I
shall consider the geological
succession of organic beings
throughout time; in the eleventh
and twelfth, their geographical
distribution throughout space;
in the thirteenth, their classification
or mutual affinities, both when
mature and in an embryonic condition.
In the last chapter I shall give
a brief recapitulation of the
whole work, and a few concluding
remarks.)
No one ought
to feel surprise at much remaining
as yet unexplained
in regard to the origin of species
and varieties, if he makes due
allowance for our profound ignorance
in regard to the mutual relations
of all the beings which live
around us. Who can explain why
one species ranges widely and
is very numerous, and why another
allied species has a narrow range
and is rare? Yet these relations
are of the highest importance,
for they determine the present
welfare, and, as I believe, the
future success and modification
of every inhabitant of this world.
Still less do we know of the
mutual relations of the innumerable
inhabitants of the world during
the many past geological epochs
in its history. Although much
remains obscure, and will long
remain obscure, I can entertain
no doubt, after the most deliberate
study and dispassionate judgement
of which I am capable, that the
view which most naturalists entertain,
and which I formerly entertained —namely,
that each species has been independently
created —is erroneous.
I am fully convinced that species
are not immutable; but that those
belonging to what are called
the same genera are lineal descendants
of some other and generally extinct
species, in the same manner as
the acknowledged varieties of
any one species are the descendants
of that species. Furthermore,
I am convinced that Natural Selection
has been the main but not exclusive
means of modification. |