On the Origin of Species (excerpt)

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 coadaptation which most justly excites our admiration.
Naturalists continually refer to external conditions, such as climate,
food, etc., 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 in 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 judgment 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.

Charles Darwin died long ago, but you'll often see
his name (framed by a fish with legs) on many a vehicle in America. This
text is public domain.

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