case of mammals, were they created bearing the false marks of nourishment
from the mother's womb? Although naturalists very properly demand a full
explanation of every difficulty from those who believe in the mutability of
species, on their own side they ignore the whole subject of the first
appearance of species in what they consider reverent silence.
It may be asked how far I extend the doctrine of the modification of
species. The question is difficult to answer, because the more distinct
the forms are which we may consider, by so much the arguments fall away in
force. But some arguments of the greatest weight extend very far. All the
members of whole classes can be connected together by chains of affinities,
and all can be classified on the same principle, in groups subordinate to
groups. Fossil remains sometimes tend to fill up very wide intervals
between existing orders. Organs in a rudimentary condition plainly show
that an early progenitor had the organ in a fully developed state; and this
in some instances necessarily implies an enormous amount of modification in
the descendants. Throughout whole classes various structures are formed on
the same pattern, and at an embryonic age the species closely resemble each
other. Therefore I cannot doubt that the theory of descent with
modification embraces all the members of the same class. I believe that
animals have descended from at most only four or five progenitors, and
plants from an equal or lesser number.
Analogy would lead me one step further, namely, to the belief that all
animals and plants have descended from some one prototype. But analogy may
be a deceitful guide. Nevertheless all living things have much in common,
in their chemical composition, their germinal vesicles, their cellular
structure, and their laws of growth and reproduction. We see this even in
so trifling a circumstance as that the same poison often similarly affects
plants and animals; or that the poison secreted by the gall-fly produces
monstrous growths on the wild rose or oak-tree. Therefore I should infer
from analogy that probably all the organic beings which have ever lived on
this earth have descended from some one primordial form, into which life
was first breathed.
When the views entertained in this volume on the origin of species, or when
analogous views are generally admitted, we can dimly foresee that there
will be a considerable revolution in natural history. Systematists will be
able to pursue their labours as at present; but they will not be
incessantly haunted by the shadowy doubt whether this or that form be in
essence a species. This I feel sure, and I speak after experience, will be
no slight relief. The endless disputes whether or not some fifty species
of British brambles are true species will cease. Systematists will have
only to decide (not that this will be easy) whether any form be
sufficiently constant and distinct from other forms, to be capable of
definition; and if definable, whether the differences be sufficiently
important to deserve a specific name. This latter point will become a far
more essential consideration than it is at present; for differences,
however slight, between any two forms, if not blended by intermediate
gradations, are looked at by most naturalists as sufficient to raise both
forms to the rank of species. Hereafter we shall be compelled to
acknowledge that the only distinction between species and well-marked
varieties is, that the latter are known, or believed, to be connected at
the present day by intermediate gradations, whereas species were formerly
thus connected. Hence, without quite rejecting the consideration of the
present existence of intermediate gradations between any two forms, we
shall be led to weigh more carefully and to value higher the actual amount
of difference between them. It is quite possible that forms now generally
acknowledged to be merely varieties may hereafter be thought worthy of
specific names, as with the primrose and cowslip; and in this case
scientific and common language will come into accordance. In short, we
shall have to treat species in the same manner as those naturalists treat
genera, who admit that genera are merely artificial combinations made for
convenience. This may not be a cheering prospect; but we shall at least be
freed from the vain search for the undiscovered and undiscoverable essence
of the term species.
The other and more general departments of natural history will rise greatly
in interest. The terms used by naturalists of affinity, relationship,
community of type, paternity, morphology, adaptive characters, rudimentary
and aborted organs, &c., will cease to be metaphorical, and will have a
plain signification. When we no longer look at an organic being as a
savage looks at a ship, as at something wholly beyond his comprehension;
when we regard every production of nature as one which has had a history;
when we contemplate every complex structure and instinct as the summing up
of many contrivances, each useful to the possessor, nearly in the same way
as when we look at any great mechanical invention as the summing up of the
labour, the experience, the reason, and even the blunders of numerous
workmen; when we thus view each organic being, how far more interesting, I
speak from experience, will the study of natural history become!
A grand and almost untrodden field of inquiry will be opened, on the causes
and laws of variation, on correlation of growth, on the effects of use and
disuse, on the direct action of external conditions, and so forth. The
study of domestic productions will rise immensely in value. A new variety
raised by man will be a far more important and interesting subject for
study than one more species added to the infinitude of already recorded
species. Our classifications will come to be, as far as they can be so
made, genealogies; and will then truly give what may be called the plan of
creation. The rules for classifying will no doubt become simpler when we
have a definite object in view. We possess no pedigrees or armorial
bearings; and we have to discover and trace the many diverging lines of
descent in our natural genealogies, by characters of any kind which have
long been inherited. Rudimentary organs will speak infallibly with respect
to the nature of long-lost structures. Species and groups of species,
which are called aberrant, and which may fancifully be called living
fossils, will aid us in forming a picture of the ancient forms of life.
Embryology will reveal to us the structure, in some degree obscured, of the
prototypes of each great class.
When we can feel assured that all the individuals of the same species, and
all the closely allied species of most genera, have within a not very
remote period descended from one parent, and have migrated from some one
birthplace; and when we better know the many means of migration, then, by
the light which geology now throws, and will continue to throw, on former
changes of climate and of the level of the land, we shall surely be enabled
to
trace in an admirable manner the former migrations of the inhabitants of
the whole world. Even at present, by comparing the differences of the
inhabitants of the sea on the opposite sides of a continent, and the nature
of the various inhabitants of that continent in relation to their apparent
means of immigration, some light can be thrown on ancient geography.
The noble science of Geology loses glory from the extreme imperfection of
the record. The crust of the earth with its embedded remains must not be
looked at as a well-filled museum, but as a poor collection made at hazard
and at rare intervals. The accumulation of each great fossiliferous
formation will be recognised as having depended on an unusual concurrence
of circumstances, and the blank intervals between the successive stages as
having been of vast duration. But we shall be able to gauge with some
security the duration of these intervals by a comparison of the preceding
and succeeding organic forms. We must be cautious in attempting to
correlate as strictly contemporaneous two formations, which include few
identical species, by the general succession of their forms of life. As
species are produced and exterminated by slowly acting and still existing
causes, and not by miraculous acts of creation and by catastrophes; and as
the most important of all causes of organic change is one which is almost
independent of altered and perhaps suddenly altered physical conditions,
namely, the mutual relation of organism to organism,--the improvement of
one being entailing the improvement or the extermination of others; it
follows, that the amount of organic change in the fossils of consecutive
formations probably serves as a fair measure of the lapse of actual time.
A number of species, however, keeping in a body might remain for a long
period unchanged, whilst within this same period, several of these species,
by migrating into new countries and coming into competition with foreign
associates, might become modified; so that we must not overrate the
accuracy of organic change as a measure of time. During early periods of
the earth's history, when the forms of life were probably fewer and
simpler, the rate of change was probably slower; and at the first dawn of
life, when very few forms of the simplest structure existed, the rate of
change may have been slow in an extreme degree. The whole history of the
world, as at present known, although of a length quite incomprehensible by
us, will hereafter be recognised as a mere fragment of time, compared with
the ages which have elapsed since the first creature, the progenitor of
innumerable extinct and living descendants, was created.
In the distant future I see open fields for far more important researches.
Psychology will be based on a new foundation, that of the necessary
acquirement of each mental power and capacity by gradation. 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 Silurian 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. And 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 of
each genus, and all the species of many genera, have left no descendants,
but have become utterly extinct. We can so far take a prophetic glance
into futurity as to foretel that it will be the common and widely-spread
species, belonging to the larger and dominant groups, 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
Silurian 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. Hence we may look with some confidence to a secure future
of equally inappreciable length. And 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 an entangled 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 on 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
external 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
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.
Subject Index
Aberrant groups
Abyssinia, plants of
Acclimatisation
Affinities of extinct species; of organic beings
Agassiz on Amblyopsis; on groups of species suddenly appearing; on
embryological succession; on the glacial period; on embryological
characters; on the embryos of vertebrata; on parallelism of embryological
development and geological succession
Algae of New Zealand
Alligators, males, fighting
Amblyopsis, blind fish
America, North, productions allied to those of Europe; boulders and
glaciers of; South, no modern formations on west coast
Ammonites, sudden extinction of
Anagallis, sterility of
Analog of variations
Ancylus
Animals, not domesticated from being variable; domestic; descended from
several stocks; acclimatisation of; of Australia; with thicker fur in cold
climates; blind, in caves; extinct, of Australia
Anomma
Antarctic islands, ancient flora of
Antirr
hinum
Ants attending aphides; slave-making instinct
Ants, neuter, structure of
Aphides attended by ants
Aphis, development of
Apteryx
Arab horses
Aralo-Caspian Sea
Archiac, M. de, on the succession of species
Artichoke, Jerusalem
Ascension, plants of
Asclepias, pollen of
Asparagus
Aspicarpa
Asses, striped
Ateuchus
Audubon, on habits of frigate-bird; on variation in birds'-nests; on heron
eating seeds
Australia, animals of; dogs of; extinct animals of; European plants in
Azara on flies destroying cattle
Azores, flora of
Babington, Mr., on British plants
Balancement of growth
Bamboo with hooks
Barberry, flowers of
Barrande, M., on Silurian colonies; on the succession of species; on
parallelism of palaeozoic formations; on affinities of ancient species
Barriers, importance of
Batrachians on islands
Bats, how structure acquired; distribution of
Bear, catching water-insects
Bee, sting of; queen, killing rivals
Bees fertilizing flowers; hive; not sucking the red clover; cell-making
instinct; humble, cells of; parasitic
Beetles, wingless, in Madeira; with deficient tarsi
Bentham, Mr., on British plants; on classification
Berkeley, Mr., on seeds in salt-water
Bermuda, birds of
Birds acquiring fear; annually cross the Atlantic; colour of, on
continents; fossil, in caves of Brazil; of Madeira, Bermuda, and Galapagos;
song of males; transporting seeds; waders; wingless; with traces of
embryonic teeth
Bizcacha, affinities of
Bladder for swimming in fish
Blindness of cave animals
Blyth, Mr., on distinctness of Indian cattle; on striped Hemionus; on
crossed geese
Boar; shoulder-pad of
Borrow, Mr., on the Spanish pointer
Bory St. Vincent, on Batrachians
Bosquet, M., on fossil Chthamalus
Boulders, erratic, on the Azores
Branchiae
Brent, Mr., on house-tumblers; on hawks killing pigeons
Brewer, Dr., on American cuckoo
Britain, mammals of
Bronn, on duration of specific forms
Brown, Robert, on classification
Buckman, on variation in plants
Buzareingues on sterility of varieties
Cabbage, varieties of, crossed
Calceolaria
Canary-birds, sterility of hybrids
Cape de Verde islands
Cape of Good Hope, plants of
Carrier-pigeons killed by hawks
Cassini on flowers of composita
Catasetum
Cats, with blue eyes, deaf; variation in habits of; curling tail when going
to spring
Cattle destroying fir-trees; destroyed by flies in La Plata; breeds of,
locally extinct; fertility of Indian and European breeds
Cave, inhabitants of, blind
Centres of creation
Cephalopodae, development of
Cervulus
Cetacea, teeth and hair
Ceylon, plants of
Chalk formation
Charlock
Checks to increase; mutual
Chickens, instinctive tameness of
Chthamalinae
Chthamalus, cretacean species of
Circumstances favourable to selection of domestic products; to natural
selection
Cirripedes capable of crossing; carapace aborted; their ovigerous frena;
fossil; larvae of
Clift, Mr., on the succession of types
Climate, effects of, in checking increase of beings; adaptation of, to
organisms