Charles Robert Darwin was born at Shrewsbury, England, Feb. 12,
1809, of a family distinguished on both sides. Abandoning medicine
for natural history, he joined H.M.S. Beagle in 1831 on the five
years' voyage, which he described in "The Voyage of the Beagle,"
and to which he refers in the introduction to his masterpiece. The
"Origin of Species" containing, in the idea of natural selection,
the distinctive contribution of Darwin to the theory of organic
evolution, was published in November, 1859. In only one brief
sentence did he there allude to man, but twelve years later he
published the "Descent of Man," in which the principles of the
earlier volume found their logical outcome. In other works Darwin
added vastly to our knowledge of coral reefs, organic variation,
earthworms, and the comparative expression of the emotions in man
and animals. Darwin died in ignorance of the work upon variation
done by his great contemporary, Gregor Mendel, whose work was
rediscovered in 1900. "Mendelism" necessitates much modification of
Darwin's work, which, however, remains the maker of the greatest
epoch in the study of life and the most important contribution to
that study ever made. Its immortal author died on April 19, 1882,
and was buried in Westminster Abbey.
_I.--Creation or Evolution?_
When on board H.M.S. Beagle as naturalist, I was much struck with
certain facts in the distribution of the organic beings inhabiting South
America, and in the geographical relations of the present to the past
inhabitants of that continent. These facts, as will be seen in the
latter chapters of this volume, seemed 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, in 1837, it occurred to me
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.
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 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 justly excites our admiration.
Naturalists continually refer to external conditions, such as climate,
food, etc., as the only possible cause of variation. In one 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 mistletoe, 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 the 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.
It is, therefore, of the highest importance to gain a clear insight into
the means of modification and co-adaptation. At the beginning 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.
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
until recently entertained, 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 also convinced that Natural Selection has been the
most important, but not the exclusive, means of modification.
_II.--Variation and Selection_
All living beings vary more or less from one another, and though
variations which are not inherited are unimportant for us, the number
and diversity of inheritable deviations of structure, both those of
slight and those of considerable physiological importance, are endless.
No breeder doubts how strong is the tendency to inheritance; that like
produces like is his fundamental belief. Doubts have been thrown on
this principle only by theoretical writers. When any deviation of
structure often appears, and we see it in the father and child, we
cannot tell whether it may not be due to the same cause having acted on
both; but when amongst individuals, apparently exposed to the same
conditions, any very rare deviation, due to some extraordinary
combination of circumstances, appears in the parent--say, once amongst
several million individuals--and it re-appears in the child, the mere
doctrine of chances almost compels us to attribute its reappearance to
inheritance.
Everyone must have heard of cases of albinism, prickly skin, hairy
bodies, etc., appearing in members of the same family. If strange and
rare deviations of structure are really inherited, less strange and
commoner deviations may be freely admitted to be inheritable. Perhaps
the correct way of viewing the whole subject would be to look at the
inheritance of every character whatever as the rule, and non-inheritance
as the anomaly.
The laws governing inheritance are for the most part unknown. No one can
say why the same peculiarity in different individuals of the same
species, or in different species, is sometimes inherited and sometimes
not so; why the child often reverts in certain characters to its
grandfather or grandmother, or more remote ancestor; why a peculiarity
is often transmitted from one sex to both sexes, or to one sex alone,
more commonly but not exclusively to the like sex.
The fact of heredity being given, we have evidence derived from human
practice as to the influence of selection. There are large numbers of
domesticated races of animals and plants admirably suited in various
ways to man's use or fancy--adapted to the environment of which his need
and inclination are the most essential constituents. We cannot suppose
that all the breeds were suddenly produced as perfect and as useful as
we now see them; indeed, in many cases, we know that this has not been
their history. The key is man's power of accumulative selection. Nature
gives successive variations; man adds them up in certain directions
useful to him. In this sense he may be said to have made for himself
useful breeds.
The great power of this principle of selection is not hypothetical. It
is certain that several of our eminent breeders have, even within a
single lifetime, modified to a large extent their breeds of cattle and
sheep. What English breeders have actually effected is proved by the
enormous prices given for animals with a good pedigree; and these have
been exported to almost every quarter of the world. The same principles
are followed by horticulturists, and we see an astonishing improvement
in many florists' flowers, when the flowers of the present day are
compared with drawings made only twenty or thirty years ago.
The practice of selection is far from being a modern discovery. The
principle of selection I find distinctly given in an ancient Chinese
encyclopædia. Explicit rules are laid down by some of the Roman
classical writers. It is clear that the breeding of domestic animals was
carefully attended to in ancient times, and is now attended to by the
lowest savages. It would, indeed, have been a strange fact had attention
not been paid to breeding, for the inheritance of good and bad qualities
is so obvious.
Study of the origin of our domestic races of animals and plants leads to
the following conclusions. Changed conditions of life are of the highest
possible importance in causing variability, both by acting directly on
the organisation, and indirectly by affecting the reproductive system.
Spontaneous variation of unknown origin plays its part. Some, perhaps a
great, effect may be attributed to the increased use or disuse of parts.
The final result is thus rendered infinitely complex. In some cases the
intercrossing of aboriginally distinct species appears to have played
an important part in the origin of our breeds. When several breeds have
once been formed in any country, their occasional intercrossing, with
the aid of selection, has, no doubt, largely aided in the formation of
new sub-breeds; but the importance of crossing has been much
exaggerated, both in regard to animals and to those plants which are
propagated by seed. Over all these causes of change, the accumulative
action of selection, whether applied methodically and quickly, or
unconsciously and slowly, but more efficiently, seems to have been the
predominant power.
_III.--Variation Under Nature_
Before applying these principles to organic beings in a state of nature,
we must ascertain whether these latter are subject to any variation. We
find variation everywhere. Individual differences, though of small
interest to the systematist, are of the highest importance for us, for
they are often inherited; and they thus afford materials for natural
selection to act and accumulate, in the same manner as man accumulates
in any given direction individual differences in his domesticated
productions. Further, what we call varieties cannot really be
distinguished from species in the long run, a fact which we can clearly
understand if species once existed as varieties, and thus originated.
But the facts are utterly inexplicable if species are independent
creations.
How have all the exquisite adaptations of one part of the body to
another part, and to the conditions of life, and of one organic being to
another being, been perfected? For everywhere we find these beautiful
adaptations.
The answer is to be found in the struggle for life. Owing to this
struggle, variations, however slight, and from whatever cause
proceeding, if they be in any degree profitable to the individuals of a
species in their infinitely complex relations to other organic beings
and to their physical conditions of life, will tend to the preservation
of such individuals, and will generally be inherited by the offspring.
The offspring, also, will thus have a better chance of surviving, for,
of the many individuals of any species which are periodically born, but
a small number can survive. I have called this principle, by which each
slight variation, if useful, is preserved, by the term Natural
Selection, in order to mark its relation to man's power of selection.
But the expression, often used by Mr. Herbert Spencer, of the Survival
of the Fittest, is more accurate.
We have seen that man, by selection, can certainly produce great
results, and can adapt organic beings to his own uses, through the
accumulation of slight but useful variations given to him by the hand of
Nature. Natural Selection is a power incessantly ready for action, and
is as immeasurably superior to man's feeble efforts as the works of
Nature are to those of Art.
All organic beings are exposed to severe competition. Nothing is easier
than to admit in words the truth of the universal struggle for life, or
more difficult--at least, I have found it so--than constantly to bear
this conclusion in mind. Yet, unless it be thoroughly engrained in the
mind, the whole economy of Nature, with every fact of distribution,
rarity, abundance, extinction, and variation, will be dimly seen or
quite misunderstood. We behold the face of Nature bright with gladness;
we often see superabundance of food. We do not see, or we forget, that
the birds which are idly singing round us mostly live on insects or
seeds, and are thus constantly destroying life; or we forget how largely
these songsters, or their eggs, or their nestlings, are destroyed by
birds or beasts of prey. We do not always bear in mind that, though food
may be superabundant, it is not so at all seasons of each recurring
year.
A struggle for existence, the term being used in a large, general, and
metaphorical sense, inevitably follows from the high rate at which all
organic beings tend to increase.
Every being, which during its natural lifetime produces several eggs or
seeds, must suffer destruction during some period of its life, and
during some season or occasional year; otherwise, on the principle of
geometrical increase, its numbers would quickly become so inordinately
great that no country could support the product. Hence, as more
individuals are produced than can possibly survive, there must in every
case be a struggle for existence, either one individual with another of
the same species, or with the individuals of distinct species, or with
the physical conditions of life. It is the doctrine of Malthus applied
with manifold force to the whole animal and vegetable kingdoms; for in
this case there can be no artificial increase of food, and no prudential
restraint from marriage. Although some species may be now increasing,
more or less rapidly, in numbers, all cannot do so, for the world would
not hold them.
There is no exception to the rule that every organic being naturally
increases at so high a rate that, if not destroyed, the earth would soon
be covered by the progeny of a single pair. Even slow-breeding man has
doubled in twenty-five years, and at this rate, in less than a thousand
years, there would literally not be standing-room for his progeny.
Linnæus has calculated that if an annual plant produced only two
seeds--and there is no plant so unproductive as this--and their
seedlings next year produced two, and so on, then in twenty years there
would be a million plants. The elephant is reckoned the slowest breeder
of all known animals, and I have taken some pains to estimate its
probable minimum rate of natural increase. It will be safest to assume
that it begins breeding when thirty years old, and goes on breeding
until ninety years old, bringing forth six young in the interval, and
surviving till one hundred years old. If this be so, after a period of
from 740 to 750 years there would be nearly nineteen million elephants
alive, descended from the first pair.
The causes which check the natural tendency of each species to increase
are most obscure. Eggs or very young animals seem generally to suffer
most, but this is not invariably the case. With plants there is a vast
destruction of seeds. The amount of food for each species of course
gives the extreme limit to which each can increase; but very frequently
it is not the obtaining food, but the serving as prey to other animals,
which determines the average number of a species. Climate is important,
and periodical seasons of extreme cold or drought seem to be the most
effective of all checks.
The relations of all animals and plants to each other in the struggle
for existence are most complex, and often unexpected. Battle within
battle must be continually recurring with varying success; and yet in
the long run the forces are so nicely balanced that the face of Nature
remains for long periods of time uniform, though assuredly the merest
trifle would give the victory to one organic being over another.
Nevertheless, so profound is our ignorance, and so high our presumption,
that we marvel when we hear of the extinction of an organic being; and
as we do not see the cause, we invoke cataclysms to desolate the world,
or invent laws on the duration of the forms of life!
The struggle for life is most severe between individuals and varieties
of the same species. The competition is most severe between allied forms
which fill nearly the same place in the economy of Nature. But great is
our ignorance on the mutual relations of all organic beings. All that we
can do is to keep steadily in mind that each organic being is striving
to increase in a geometrical ratio; that each at some period of its
life, during some season of the year, during each generation or at
intervals, has to struggle for life and to suffer great destruction.
When we reflect on this struggle, we may console ourselves with the full
belief that the war of Nature is not incessant, that no fear is felt,
that death is generally prompt, and that the vigorous, the healthy, and
the happy survive and multiply.
_IV.--The Survival of the Fittest_
How will the struggle for existence act in regard to variation? Can the
principle of selection, which we have seen is so potent in the hands of
man, apply under Nature? I think we shall see that it can act most
efficiently. Let the endless number of slight variations and individual
differences occurring in our domestic productions, and, in a lesser
degree, in those under Nature, be borne in mind, as well as the strength
of the hereditary tendency. Under domestication, it may be truly said
that the whole organisation becomes in some degree plastic.
But the variability, which we almost universally meet with in our
domestic productions, is not directly produced by man; he can neither
originate variations nor prevent their occurrence; he can only preserve
and accumulate such as do occur. Unintentionally he exposes organic
beings to new and changing conditions of life, and variability ensues;
but similar changes of condition might and do occur under Nature.
Let it also be borne in mind how infinitely complex and close-fitting
are the mutual relations of all organic beings to each other and to
their physical conditions of life, and consequently what infinitely
varied diversities of structure might be of use to each being under
changing conditions of life. Can it, then, be thought improbable, seeing
what variations useful to man have undoubtedly occurred, that other
variations, useful in some way to each being in the great complex battle
of life, should occur in the course of many successive generations? If
such do occur, can we doubt, remembering that many more individuals are
born than can possibly survive, that individuals having any advantage
over others, would have the best chance of surviving and of procreating
their kind? On the other hand, we may feel sure that any variation in
the least degree injurious would be rigidly destroyed. This preservation
of favourable individual differences and variations, and the destruction
of those which are injurious, I have called Natural Selection, or the
Survival of the Fittest.
The term is too frequently misapprehended. Variations neither useful nor
injurious would not be affected by natural selection. It is not asserted
that natural selection induces variability. It implies only the
preservation of such varieties as arise and are beneficial to the being
under its conditions of life. Again, it has been said that I speak of
natural selection as an active Power or Deity; but who objects to an
author speaking of the attraction of gravity as ruling the movements of
the planets? It is difficult to avoid personifying the word Nature; but
I mean by Nature only the aggregate action and product of many natural
laws, and by laws the sequence of events as ascertained by us.
As man can produce, and certainly has produced, a great result by his
methodical and unconscious means of selection, what may not natural
selection effect? Man can act only on external and visible characters;
Nature, if I may be allowed to personify the natural preservation or
survival of the fittest, cares nothing for appearances, except in so far
as they are useful to any being. She can act on every internal organ, on
every shade of constitutional difference, on the whole machinery of
life. Man selects only for his own good; Nature only for that of the
being which she tends. Every selected character is fully exercised by
her, as is implied by the fact of their selection. Man keeps the natives
of many climates in the same country; he seldom exercises each selected
character in some peculiar and fitting manner; he feeds a long and a
short-beaked pigeon on the same food; he does not exercise a long-backed
or long-legged quadruped in any peculiar manner; he exposes sheep with
long and short wool to the same climate.
Man does not allow the most vigorous males to struggle for the females.
He does not rigidly destroy all inferior animals, but protects during
each varying season, as far as lies in his power, all his productions.
He often begins his selection by some half-monstrous form; or at least
by some modification prominent enough to catch the eye or to be plainly
useful to him.
But under Nature, the slightest differences of structure or constitution
may well turn the nicely-balanced scale in the struggle for life, and so
be preserved. How fleeting are the wishes and efforts of man! How short
his time! And, consequently, how poor will be his results compared with
those accumulated by Nature during whole geological periods! Can we
wonder that Nature's productions should be far "truer" in character than
man's productions; that they should be infinitely better adapted to the
most complex conditions of life, and should plainly bear the stamp of
far higher workmanship?
It may metaphorically be said that natural selection is daily and hourly
scrutinising, throughout the world, the slightest variations; rejecting
those that are bad, preserving and adding up all that are good; silently
and insensibly working, whenever and wherever opportunity offers, at the
improvement of each organic being in relation to its organic and
inorganic conditions of life. We see nothing of these slow changes in
progress until the hand of time has marked the lapse of ages, and then
so imperfect is our view into long-past geological ages that we see only
that the forms of life are now different from what they formerly were.
Although natural selection can act only through and for the good of
each being, yet characters and structures, which we are apt to consider
as of very trifling importance, may thus be acted on.
Natural selection will modify the structure of the young in relation to
the parent, and of the parent in relation to the young. In social
animals it will adapt the structure of each individual for the benefit
of the whole community, if the community profits by the selected change.
What natural selection cannot do is to modify the structure of one
species, without giving it any advantage, for the good of another
species; and though statements to this effect may be found in works of
natural history, I cannot find one case which will bear investigation.
A structure used only once in an animal's life, if of high importance to
it, might be modified to any extent by natural selection; for instance,
the great jaws possessed by certain insects, used exclusively for
opening the cocoon, or the hard tip to the beak of unhatched birds, used
for breaking the egg. It has been asserted that of the best short-beaked
tumbler pigeons a greater number perish in the egg than are able to get
out of it; so that fanciers assist in the act of hatching. Now, if
Nature had to make the beak of a full-grown pigeon very short for the
bird's own advantage, the process of modification would be very slow,
and there would be simultaneously the most rigorous selection of all the
young birds within the egg, for all with weak beaks would inevitably
perish; or more easily broken shells might be selected, the thickness of
the shell being known to vary like every other structure.
With all beings there must be much fortuitous destruction, which can
have little or no influence on the course of natural selection. For
instance, a vast number of eggs or seeds are annually devoured, and
these could be modified through natural selection only if they varied
in some manner which protected them from their enemies. Yet many of
these eggs or seeds would perhaps, if not destroyed, have yielded
individuals better adapted to their conditions of life than any of those
which happened to survive. So, again, a vast number of mature animals
and plants, whether or not they be the best adapted to their conditions,
must be annually destroyed by accidental causes, which would not be in
the least degree mitigated by certain changes of structure or
constitution which would in other ways be beneficial to the species.
But let the destruction of the adults be ever so heavy, if the number
which can exist in any district be not wholly kept down by such
causes--or, again, let the destruction of eggs or seeds be so great that
only a hundredth or a thousandth part are developed--yet of those which
do survive, the best adapted individuals, supposing there is any
variability in a favourable direction, will tend to propagate their kind
in larger numbers than the less well adapted.
On our theory the continued existence of lowly organisms offers no
difficulty; for natural selection does not necessarily include
progressive development; it only takes advantage of such variations as
arise and are beneficial to each creature under its complex relations of
life.
The mere lapse of time by itself does nothing, either for or against
natural selection. I state this because it has been erroneously asserted
that the element of time has been assumed by me to play an all-important
part in modifying species, as if all the forms of life were necessarily
undergoing change through some innate law.
_V.--Sexual Selection_
This form of selection depends, not on a struggle for existence in
relation to other organic beings or to external conditions, but on a
struggle between the individuals of one sex, generally the males, for
the possession of the other sex. The result is not death to the
unsuccessful competitor, but few or no offspring. Sexual selection is,
therefore, less rigorous than natural selection. Generally, the most
vigorous males, those which are best fitted for their places in Nature,
will leave most progeny. But, in many cases, victory depends not so much
on general vigour as on having special weapons, confined to the male
sex. A hornless stag or spurless cock would have a poor chance of
leaving numerous offspring. Sexual selection, by always allowing the
victor to breed, might surely give indomitable courage, length to the
spur, and strength to the wing to strike in the spurred leg, in nearly
the same manner as does the brutal cock-fighter by the careful selection
of his best cocks.
How low in the scale of Nature the law of battle descends I know not.
Male alligators have been described as fighting, bellowing, and whirling
round, like Indians in a war-dance, for the possession of the females;
male salmons have been observed fighting all day long; male stag-beetles
sometimes bear wounds from the mandibles of other males; the males of
certain other insects have been frequently seen fighting for a
particular female who sits by, an apparently unconcerned beholder of the
struggle, and then retires with the conqueror. The war is, perhaps,
severest between the males of the polygamous animals, and these seem
oftenest provided with special weapons. The males of carnivorous animals
are already well armed, though to them special means of defence may be
given through means of sexual selection, as the mane of the lion and the
hooked jaw of the salmon. The shield may be as important for victory as
the sword or spear.
Amongst birds, the contest is often of a more peaceful character. All
those who have attended to the subject believe that there is the
severest rivalry between the males of many species to attract, by
singing, the females. The rock-thrush of Guiana, birds of paradise, and
some others, congregate; and successive males display with the most
elaborate care, and show off in the best manner, their gorgeous plumage;
they likewise perform strange antics before the females, which, standing
by as spectators, at last choose the most attractive partner.
If man can in a short time give beauty and an elegant carriage to his
bantams, according to his standard of beauty, I can see no good reason
to doubt that female birds, by selecting, during thousands of
generations, the most melodious or beautiful males, according to their
standard of beauty, might produce a marked effect.
_VI.--The Struggle for Existence_
Under domestication we see much variability, caused, or at least
excited, by changed conditions of life; but often in so obscure a manner
that we are tempted to consider the variations as spontaneous.
Variability is governed by many complex laws--by correlated growth,
compensation, the increased use and disuse of parts, and the definite
action of the surrounding conditions. There is much difficulty in
ascertaining how largely our domestic productions have been modified;
but we may safely infer that the amount has been large, and that
modifications can be inherited for long periods. As long as the
conditions of life remain the same, we have reason to believe that a
modification, which has already been inherited for many generations, may
continue to be inherited for an almost infinite number of generations.
On the other hand, we have evidence that variability, when it has once
come into play, does not cease under domestication for a very long
period; nor do we know that it ever ceases, for new varieties are still
occasionally produced by our oldest domesticated productions.
Variability is not actually caused by man; he only unintentionally
exposes organic beings to new conditions of life, and then Nature acts
on the organisation and causes it to vary. But man can and does select
the variations given to him by Nature, and thus accumulates them in any
desired manner. He thus adapts animals and plants for his own benefit or
pleasure. He may do this methodically, or he may do it unconsciously by
preserving the individuals most useful or pleasing to him without an
intention of altering the breed.
It is certain that he can influence the character of a breed by
selecting, in each successive generation, individual differences so
slight as to be inappreciable except by an educated eye. This
unconscious process of selection has been the agency in the formation of
the most distinct and useful domestic breeds. That many breeds produced
by man have to a large extent the character of natural species is shown
by the inextricable doubts whether many of them are varieties or
aboriginally distinct species.
There is no reason why the principles which have acted so efficiently
under domestication should not have acted under Nature. In the survival
of favoured individuals and races, during the constantly recurrent
struggle for existence, we see a powerful and ever-acting form of
selection. The struggle for existence inevitably follows from the high
geometrical ratio of increase which is common to all organic beings.
This high rate of increase is proved by calculation; by the rapid
increase of many animals and plants during a succession of peculiar
seasons and when naturalised in new countries. More individuals are born
than can possibly survive. A grain in the balance may determine which
individuals shall live and which shall die; which variety or species
shall increase in number, and which shall decrease, or finally become
extinct.
As the individuals of the same species come in all respects into the
closest competition with each other, the struggle will generally be
most severe between them; it will be almost equally severe between the
varieties of the same species, and next in severity between the species
of the same genus. On the other hand, the struggle will often be severe
between beings remote in the scale of Nature. The slightest advantage in
certain individuals, at any age or during any season, over those with
which they come into competition, or better adaptation, in however
slight a degree, to the surrounding physical conditions, will, in the
long run, turn the balance.
With animals having separated sexes, there will be in most cases a
struggle between the males for the possession of the females. The most
vigorous males, or those which have most successfully struggled with
their conditions of life, will generally leave most progeny. But success
will often depend on the males having special weapons, or means of
defence, or charms; and a slight advantage will lead to victory.
As geology plainly proclaims that each land has undergone great physical
changes, we might have expected to find that organic beings have varied
under Nature in the same way as they have varied under domestication.
And if there has been any variability under Nature, it would be an
unaccountable fact if natural selection had not come into play. It has
often been asserted, but the assertion is incapable of proof, that the
amount of variation under Nature is a strictly limited quantity. Man,
though acting on external characters alone, and often capriciously, can
produce within a short period a great result by adding up mere
individual differences in his domestic productions; and everyone admits
that species present individual differences. But, besides such
differences, all naturalists admit that natural varieties exist, which
are considered sufficiently distinct to be worthy of record in
systematic works.
No one has drawn any clear distinction between individual differences
and slight varieties, or between more plainly marked varieties and
sub-species and species. On separate continents, and on different parts
of the same continent when divided by barriers of any kind, what a
multitude of forms exist which some experienced naturalists rank as
varieties, others as geographical races or sub-species, and others as
distinct, though closely allied species!
If, then, animals and plants do vary, let it be ever so slightly or
slowly, why should not variations or individuals, differences which are
in any way beneficial, be preserved and accumulated through natural
selection, or the survival of the fittest? If man can, by patience,
select variations useful to him, why, under changing and complex
conditions of life, should not variations useful to Nature's living
products often arise, and be preserved, or selected? What limit can be
put to this power, acting during long ages and rigidly scrutinising the
whole constitution, structure, and habits of each creature--favouring
the good and rejecting the bad? I can see no limit to this power, in
slowly and beautifully adapting each form to the most complex relations
of life.
In the future I see open fields for far more important researches.
Psychology will be based on the foundation already well laid by Mr.
Herbert Spencer--that of the necessary acquirement of each mental power
and capacity by gradation. Much light will be thrown on the origin of
man and his history.
Authors of the highest eminence seem to be fully satisfied with the view
that each species has been independently created. To my mind it accords
better with what we know of the laws impressed on matter by the Creator
that the production and extinction of the past and present inhabitants
of the world should have been due to secondary causes, like those
determining the birth and death of the individual. When I view all
beings not as special creations, but as the lineal descendants of some
few beings which lived long before the first bed of the Cambrian system
was deposited, they seem to me to become ennobled. Judging from the
past, we may safely infer that not one living species will transmit its
unaltered likeness to a distant futurity.
Of the species now living very few will transmit progeny of any kind to
a far distant futurity; for the manner in which all organic beings are
grouped shows that the greater number of species in each genus, and all
the species in many genera, have left no descendants, but have become
utterly extinct. We can so far take a prophetic glance into futurity as
to foretell that it will be the common and widely-spread species,
belonging to the larger and dominant groups within each class, which
will ultimately prevail and procreate new and dominant species. As all
the living forms of life are the lineal descendants of those which lived
long before the Cambrian epoch, we may feel certain that the ordinary
succession by generation has never once been broken, and that no
cataclysm has desolated the whole world. We may look with some
confidence to a secure future of great length. As natural selection
works solely by and for the good of each being, all corporeal and mental
endowments will tend to progress towards perfection.
It is interesting to contemplate a tangled bank, clothed with many
plants of many kinds, with birds singing on the bushes, with various
insects flitting about, and with worms crawling through the damp earth,
and to reflect that these elaborately constructed forms, so different
from each other, and dependent upon each other in so complex a manner,
have all been produced by laws acting around us. These laws, taken in
the largest sense, being Growth with Reproduction; Inheritance, which is
almost implied by reproduction; Variability from the indirect and direct
action of the conditions of life, and from use and disuse; a ratio of
increase so high as to lead to a struggle for life, and, as a
consequence, to Natural Selection, entailing Divergence of Character
and the Extinction of less improved forms. Thus, from the war of Nature,
from famine and death, the most exalted object which we are capable of
conceiving, namely, the production of the higher animals, directly
follows. There is grandeur in this view of life, with its several
powers, having been originally breathed by the Creator into a few forms,
or into one; and that, whilst this planet has gone cycling on according
to the fixed law of gravity, from so simple a beginning endless forms
most beautiful and most wonderful have been, and are being, evolved.