scended, like varieties, from other species. Nevertheless
such a conclusion, even if well founded, would be unsat-
isfactory, 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, &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 abso-
lutely requiring the agency of certain insects to bring pol-
len from one flower to the other, it is equally preposterous
to account for the structure of this parasite, with its rela-
tions to several distinct organic beings, by the effects of
external conditions, or of habit, or of the volition of the
plant itself.

It is, therefore, of the highest importance to gain a
clear insight into the means of modification and coadapta-
tion. At the commencement of my observations it seemed
to me probable that a careful study of domesticated ani-
mals 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 Domestica-
tion. 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 or
ganic beings throughout the world, which inevitably fol
lows 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 pos-
sibly 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 con
ditions of life, will have a better chance of surviving, ano
thus be naturally selected. From the strong principle of
inheritance, any selected variety will tend to propagat
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 con-
structed organ; secondly, the subject of Instinct, or the
mental powers of animals; thirdly, Hybridism, or the in-
fertility of species and the fertility of varieties when inter-
crossed; and fourthly, the imperfection of the Geological
Record. In the next chapter I shall consider the geolog
ical 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 enter tained—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 exclu sive means of modification.

CHAPTER I.

VARIATION UNDER DOMESTICATION.

Causes of Variability-Effects of Habit-Correlation of Growth-Inheritance-Char acter of Domestic Varieties-Difficulty of distinguishing between Varieties and Species-Origin of Domestic Varieties from one or more Species-Domestic Pigeons, their Dfferences and Origin-Principle of Selection anciently followed, its Effects-Methodical and Unconscious Selection-Unknown Origin of our Domestic Productions-Circumstances favourable to Man's power of Selection.

WHEN We look to the individuals of the same variety or sub-variety of our older cultivated plants and animals, one of the first points which strikes us, is, that they gen erally differ much more from each other, than do the individuals of any one species or variety in a state of nature. When we reflect on the vast diversity of the plants and animals which have been cultivated, and which have varied during all ages under the most different climates and treatment, I think we are driven to conclude that this greater variability is simply due to our domestic productions having been raised under conditions of life not so uniform as, and somewhat different from, those to which the parent-species have been exposed under nature. There is, also, I think, some probability in the view propounded by Andrew Knight, that this variability may be partly connected with excess of food. It seems pretty clear that organic beings must be exposed during several generations to the new conditions of life to cause any appreciable amount of variation; and that when the organisation has once begun to vary, it generally continues to vary for many generations. No case is on record of a variable being ceasing to be variable under cultivation. Our oldest cultivated plants, such as wheat, still often yield new varieties: our oldest domesticated animals are still capable of rapid improvement or modification.

It has been disputed at what period of life, the causes of variability, whatever they may be, generally act; whether during the early or late period of development of the embryo, or at the instant of conception. Geoffroy St. Hilaire's experiments show that unnatural treatment of the embryo causes monstrosities; and monstrosities cannot be separated by any clear line of distinction from mere variations. But I am strongly inclined to suspect that the most frequent cause of variability may be attributed to the male and female reproductive elements having been affected prior to the act of conception. Several reasons make me believe in this; but the chief one is the remarkable effect which confinement or cultivation has on the functions of the reproductive system; this system appearing to be far more susceptible than any other part of the organisation, to the action of any change in the conditions of life. Nothing is more easy than to tame an animal, and few things more difficult than to get it to breed freely under confinement, even in the many cases when the male and female unite. How many animals there are which will not breed, though living long under not very close confinement in their native country! This is generally attributed to vitiated instincts; but how many cultivated plants display the utmost vigour, and yet rarely or never seed! In some few such cases it has been found out that very trifling changes, such as a little more or less water at some particular period of growth, will determine whether or not the plant sets a seed. I cannot here enter on the copious details which I have collected on this curious subject; but to show how singular the laws are which determine the reproduction of animals under confinement, I may just mention that carnivorous animals, even from the tropics, breed in this country pretty freely under cofinement, with the exception of the plantigrades or bear family; whereas, carnivorous birds, with the rarest exceptions, hardly ever lay fertile eggs. Many exotic plants have pollen utterly worthless, in the same exact condition as in the most sterile hybrids. When, on the one hand, we see domesticated animals and plants, though often weak and sickly, yet breeding quite freely