On the Origin of Species
by
Charles Darwin
Part 8 out of 9
the existence of varieties, which they think sufficiently distinct to
be worthy of record in systematic works. No one can draw any clear
distinction between individual differences and slight varieties; or
between more plainly marked varieties and sub-species, and species.
Let it be observed how naturalists differ in the rank which they
assign to the many representative forms in Europe and North America.
If then we have under nature variability and a powerful agent always
ready to act and select, why should we doubt that variations in any
way useful to beings, under their excessively complex relations of
life, would be preserved, accumulated, and inherited? Why, if man can
by patience select variations most useful to himself, should nature
fail in selecting variations useful, under changing conditions of
life, to her living products? 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. The theory of natural selection, even if we looked
no further than this, seems to me to be in itself probable. I have
already recapitulated, as fairly as I could, the opposed difficulties
and objections: now let us turn to the special facts and arguments in
favour of the theory.
On the view that species are only strongly marked and permanent
varieties, and that each species first existed as a variety, we can
see why it is that no line of demarcation can be drawn between
species, commonly supposed to have been produced by special acts of
creation, and varieties which are acknowledged to have been produced
by secondary laws. On this same view we can understand how it is that
in each region where many species of a genus have been produced, and
where they now flourish, these same species should present many
varieties; for where the manufactory of species has been active, we
might expect, as a general rule, to find it still in action; and this
is the case if varieties be incipient species. Moreover, the species
of the larger genera, which afford the greater number of varieties or
incipient species, retain to a certain degree the character of
varieties; for they differ from each other by a less amount of
difference than do the species of smaller genera. The closely allied
species also of the larger genera apparently have restricted ranges,
and they are clustered in little groups round other species--in which
respects they resemble varieties. These are strange relations on the
view of each species having been independently created, but are
intelligible if all species first existed as varieties.
As each species tends by its geometrical ratio of reproduction to
increase inordinately in number; and as the modified descendants of
each species will be enabled to increase by so much the more as they
become more diversified in habits and structure, so as to be enabled
to seize on many and widely different places in the economy of nature,
there will be a constant tendency in natural selection to preserve the
most divergent offspring of any one species. Hence during a
long-continued course of modification, the slight differences,
characteristic of varieties of the same species, tend to be augmented
into the greater differences characteristic of species of the same
genus. New and improved varieties will inevitably supplant and
exterminate the older, less improved and intermediate varieties; and
thus species are rendered to a large extent defined and distinct
objects. Dominant species belonging to the larger groups tend to give
birth to new and dominant forms; so that each large group tends to
become still larger, and at the same time more divergent in character.
But as all groups cannot thus succeed in increasing in size, for the
world would not hold them, the more dominant groups beat the less
dominant. This tendency in the large groups to go on increasing in
size and diverging in character, together with the almost inevitable
contingency of much extinction, explains the arrangement of all the
forms of life, in groups subordinate to groups, all within a few great
classes, which we now see everywhere around us, and which has
prevailed throughout all time. This grand fact of the grouping of all
organic beings seems to me utterly inexplicable on the theory of
creation.
As natural selection acts solely by accumulating slight, successive,
favourable variations, it can produce no great or sudden modification;
it can act only by very short and slow steps. Hence the canon of
"Natura non facit saltum," which every fresh addition to our knowledge
tends to make more strictly correct, is on this theory simply
intelligible. We can plainly see why nature is prodigal in variety,
though niggard in innovation. But why this should be a law of nature
if each species has been independently created, no man can explain.
Many other facts are, as it seems to me, explicable on this theory.
How strange it is that a bird, under the form of woodpecker, should
have been created to prey on insects on the ground; that upland geese,
which never or rarely swim, should have been created with webbed feet;
that a thrush should have been created to dive and feed on sub-aquatic
insects; and that a petrel should have been created with habits and
structure fitting it for the life of an auk or grebe! and so on in
endless other cases. But on the view of each species constantly trying
to increase in number, with natural selection always ready to adapt
the slowly varying descendants of each to any unoccupied or
ill-occupied place in nature, these facts cease to be strange, or
perhaps might even have been anticipated.
As natural selection acts by competition, it adapts the inhabitants of
each country only in relation to the degree of perfection of their
associates; so that we need feel no surprise at the inhabitants of any
one country, although on the ordinary view supposed to have been
specially created and adapted for that country, being beaten and
supplanted by the naturalised productions from another land. Nor ought
we to marvel if all the contrivances in nature be not, as far as we
can judge, absolutely perfect; and if some of them be abhorrent to our
ideas of fitness. We need not marvel at the sting of the bee causing
the bee's own death; at drones being produced in such vast numbers for
one single act, and being then slaughtered by their sterile sisters;
at the astonishing waste of pollen by our fir-trees; at the
instinctive hatred of the queen bee for her own fertile daughters; at
ichneumonidae feeding within the live bodies of caterpillars; and at
other such cases. The wonder indeed is, on the theory of natural
selection, that more cases of the want of absolute perfection have not
been observed.
The complex and little known laws governing variation are the same, as
far as we can see, with the laws which have governed the production of
so-called specific forms. In both cases physical conditions seem to
have produced but little direct effect; yet when varieties enter any
zone, they occasionally assume some of the characters of the species
proper to that zone. In both varieties and species, use and disuse
seem to have produced some effect; for it is difficult to resist this
conclusion when we look, for instance, at the logger-headed duck,
which has wings incapable of flight, in nearly the same condition as
in the domestic duck; or when we look at the burrowing tucutucu, which
is occasionally blind, and then at certain moles, which are habitually
blind and have their eyes covered with skin; or when we look at the
blind animals inhabiting the dark caves of America and Europe. In both
varieties and species correlation of growth seems to have played a
most important part, so that when one part has been modified other
parts are necessarily modified. In both varieties and species
reversions to long-lost characters occur. How inexplicable on the
theory of creation is the occasional appearance of stripes on the
shoulder and legs of the several species of the horse-genus and in
their hybrids! How simply is this fact explained if we believe that
these species have descended from a striped progenitor, in the same
manner as the several domestic breeds of pigeon have descended from
the blue and barred rock-pigeon!
On the ordinary view of each species having been independently
created, why should the specific characters, or those by which the
species of the same genus differ from each other, be more variable
than the generic characters in which they all agree? Why, for
instance, should the colour of a flower be more likely to vary in any
one species of a genus, if the other species, supposed to have been
created independently, have differently coloured flowers, than if all
the species of the genus have the same coloured flowers? If species
are only well-marked varieties, of which the characters have become in
a high degree permanent, we can understand this fact; for they have
already varied since they branched off from a common progenitor in
certain characters, by which they have come to be specifically
distinct from each other; and therefore these same characters would be
more likely still to be variable than the generic characters which
have been inherited without change for an enormous period. It is
inexplicable on the theory of creation why a part developed in a very
unusual manner in any one species of a genus, and therefore, as we may
naturally infer, of great importance to the species, should be
eminently liable to variation; but, on my view, this part has
undergone, since the several species branched off from a common
progenitor, an unusual amount of variability and modification, and
therefore we might expect this part generally to be still variable.
But a part may be developed in the most unusual manner, like the wing
of a bat, and yet not be more variable than any other structure, if
the part be common to many subordinate forms, that is, if it has been
inherited for a very long period; for in this case it will have been
rendered constant by long-continued natural selection.
Glancing at instincts, marvellous as some are, they offer no greater
difficulty than does corporeal structure on the theory of the natural
selection of successive, slight, but profitable modifications. We can
thus understand why nature moves by graduated steps in endowing
different animals of the same class with their several instincts. I
have attempted to show how much light the principle of gradation
throws on the admirable architectural powers of the hive-bee. Habit no
doubt sometimes comes into play in modifying instincts; but it
certainly is not indispensable, as we see, in the case of neuter
insects, which leave no progeny to inherit the effects of
long-continued habit. On the view of all the species of the same genus
having descended from a common parent, and having inherited much in
common, we can understand how it is that allied species, when placed
under considerably different conditions of life, yet should follow
nearly the same instincts; why the thrush of South America, for
instance, lines her nest with mud like our British species. On the
view of instincts having been slowly acquired through natural
selection we need not marvel at some instincts being apparently not
perfect and liable to mistakes, and at many instincts causing other
animals to suffer.
If species be only well-marked and permanent varieties, we can at once
see why their crossed offspring should follow the same complex laws in
their degrees and kinds of resemblance to their parents,--in being
absorbed into each other by successive crosses, and in other such
points,--as do the crossed offspring of acknowledged varieties. On the
other hand, these would be strange facts if species have been
independently created, and varieties have been produced by secondary
laws.
If we admit that the geological record is imperfect in an extreme
degree, then such facts as the record gives, support the theory of
descent with modification. New species have come on the stage slowly
and at successive intervals; and the amount of change, after equal
intervals of time, is widely different in different groups. The
extinction of species and of whole groups of species, which has played
so conspicuous a part in the history of the organic world, almost
inevitably follows on the principle of natural selection; for old
forms will be supplanted by new and improved forms. Neither single
species nor groups of species reappear when the chain of ordinary
generation has once been broken. The gradual diffusion of dominant
forms, with the slow modification of their descendants, causes the
forms of life, after long intervals of time, to appear as if they had
changed simultaneously throughout the world. The fact of the fossil
remains of each formation being in some degree intermediate in
character between the fossils in the formations above and below, is
simply explained by their intermediate position in the chain of
descent. The grand fact that all extinct organic beings belong to the
same system with recent beings, falling either into the same or into
intermediate groups, follows from the living and the extinct being the
offspring of common parents. As the groups which have descended from
an ancient progenitor have generally diverged in character, the
progenitor with its early descendants will often be intermediate in
character in comparison with its later descendants; and thus we can
see why the more ancient a fossil is, the oftener it stands in some
degree intermediate between existing and allied groups. Recent forms
are generally looked at as being, in some vague sense, higher than
ancient and extinct forms; and they are in so far higher as the later
and more improved forms have conquered the older and less improved
organic beings in the struggle for life. Lastly, the law of the long
endurance of allied forms on the same continent,--of marsupials in
Australia, of edentata in America, and other such cases,--is
intelligible, for within a confined country, the recent and the
extinct will naturally be allied by descent.
Looking to geographical distribution, if we admit that there has been
during the long course of ages much migration from one part of the
world to another, owing to former climatal and geographical changes
and to the many occasional and unknown means of dispersal, then we can
understand, on the theory of descent with modification, most of the
great leading facts in Distribution. We can see why there should be so
striking a parallelism in the distribution of organic beings
throughout space, and in their geological succession throughout time;
for in both cases the beings have been connected by the bond of
ordinary generation, and the means of modification have been the same.
We see the full meaning of the wonderful fact, which must have struck
every traveller, namely, that on the same continent, under the most
diverse conditions, under heat and cold, on mountain and lowland, on
deserts and marshes, most of the inhabitants within each great class
are plainly related; for they will generally be descendants of the
same progenitors and early colonists. On this same principle of former
migration, combined in most cases with modification, we can
understand, by the aid of the Glacial period, the identity of some few
plants, and the close alliance of many others, on the most distant
mountains, under the most different climates; and likewise the close
alliance of some of the inhabitants of the sea in the northern and
southern temperate zones, though separated by the whole intertropical
ocean. Although two areas may present the same physical conditions of
life, we need feel no surprise at their inhabitants being widely
different, if they have been for a long period completely separated
from each other; for as the relation of organism to organism is the
most important of all relations, and as the two areas will have
received colonists from some third source or from each other, at
various periods and in different proportions, the course of
modification in the two areas will inevitably be different.
On this view of migration, with subsequent modification, we can see
why oceanic islands should be inhabited by few species, but of these,
that many should be peculiar. We can clearly see why those animals
which cannot cross wide spaces of ocean, as frogs and terrestrial
mammals, should not inhabit oceanic islands; and why, on the other
hand, new and peculiar species of bats, which can traverse the ocean,
should so often be found on islands far distant from any continent.
Such facts as the presence of peculiar species of bats, and the
absence of all other mammals, on oceanic islands, are utterly
inexplicable on the theory of independent acts of creation.
The existence of closely allied or representative species in any two
areas, implies, on the theory of descent with modification, that the
same parents formerly inhabited both areas; and we almost invariably
find that wherever many closely allied species inhabit two areas, some
identical species common to both still exist. Wherever many closely
allied yet distinct species occur, many doubtful forms and varieties
of the same species likewise occur. It is a rule of high generality
that the inhabitants of each area are related to the inhabitants of
the nearest source whence immigrants might have been derived. We see
this in nearly all the plants and animals of the Galapagos
archipelago, of Juan Fernandez, and of the other American islands
being related in the most striking manner to the plants and animals of
the neighbouring American mainland; and those of the Cape de Verde
archipelago and other African islands to the African mainland. It must
be admitted that these facts receive no explanation on the theory of
creation.
The fact, as we have seen, that all past and present organic beings
constitute one grand natural system, with group subordinate to group,
and with extinct groups often falling in between recent groups, is
intelligible on the theory of natural selection with its contingencies
of extinction and divergence of character. On these same principles we
see how it is, that the mutual affinities of the species and genera
within each class are so complex and circuitous. We see why certain
characters are far more serviceable than others for
classification;--why adaptive characters, though of paramount
importance to the being, are of hardly any importance in
classification; why characters derived from rudimentary parts, though
of no service to the being, are often of high classificatory value;
and why embryological characters are the most valuable of all. The
real affinities of all organic beings are due to inheritance or
community of descent. The natural system is a genealogical
arrangement, in which we have to discover the lines of descent by the
most permanent characters, however slight their vital importance may
be.
The framework of bones being the same in the hand of a man, wing of a
bat, fin of the porpoise, and leg of the horse,--the same number of
vertebrae forming the neck of the giraffe and of the elephant,--and
innumerable other such facts, at once explain themselves on the theory
of descent with slow and slight successive modifications. The
similarity of pattern in the wing and leg of a bat, though used for
such different purpose,--in the jaws and legs of a crab,--in the
petals, stamens, and pistils of a flower, is likewise intelligible on
the view of the gradual modification of parts or organs, which were
alike in the early progenitor of each class. On the principle of
successive variations not always supervening at an early age, and
being inherited at a corresponding not early period of life, we can
clearly see why the embryos of mammals, birds, reptiles, and fishes
should be so closely alike, and should be so unlike the adult forms.
We may cease marvelling at the embryo of an air-breathing mammal or
bird having branchial slits and arteries running in loops, like those
in a fish which has to breathe the air dissolved in water, by the aid
of well-developed branchiae.
Disuse, aided sometimes by natural selection, will often tend to
reduce an organ, when it has become useless by changed habits or under
changed conditions of life; and we can clearly understand on this view
the meaning of rudimentary organs. But disuse and selection will
generally act on each creature, when it has come to maturity and has
to play its full part in the struggle for existence, and will thus
have little power of acting on an organ during early life; hence the
organ will not be much reduced or rendered rudimentary at this early
age. The calf, for instance, has inherited teeth, which never cut
through the gums of the upper jaw, from an early progenitor having
well-developed teeth; and we may believe, that the teeth in the mature
animal were reduced, during successive generations, by disuse or by
the tongue and palate having been fitted by natural selection to
browse without their aid; whereas in the calf, the teeth have been
left untouched by selection or disuse, and on the principle of
inheritance at corresponding ages have been inherited from a remote
period to the present day. On the view of each organic being and each
separate organ having been specially created, how utterly inexplicable
it is that parts, like the teeth in the embryonic calf or like the
shrivelled wings under the soldered wing-covers of some beetles,
should thus so frequently bear the plain stamp of inutility! Nature
may be said to have taken pains to reveal, by rudimentary organs and
by homologous structures, her scheme of modification, which it seems
that we wilfully will not understand.
I have now recapitulated the chief facts and considerations which have
thoroughly convinced me that species have changed, and are still
slowly changing by the preservation and accumulation of successive
slight favourable variations. Why, it may be asked, have all the most
eminent living naturalists and geologists rejected this view of the
mutability of species? It cannot be asserted that organic beings in a
state of nature are subject to no variation; it cannot be proved that
the amount of variation in the course of long ages is a limited
quantity; no clear distinction has been, or can be, drawn between
species and well-marked varieties. It cannot be maintained that
species when intercrossed are invariably sterile, and varieties
invariably fertile; or that sterility is a special endowment and sign
of creation. The belief that species were immutable productions was
almost unavoidable as long as the history of the world was thought to
be of short duration; and now that we have acquired some idea of the
lapse of time, we are too apt to assume, without proof, that the
geological record is so perfect that it would have afforded us plain
evidence of the mutation of species, if they had undergone mutation.
But the chief cause of our natural unwillingness to admit that one
species has given birth to other and distinct species, is that we are
always slow in admitting any great change of which we do not see the
intermediate steps. The difficulty is the same as that felt by so many
geologists, when Lyell first insisted that long lines of inland cliffs
had been formed, and great valleys excavated, by the slow action of
the coast-waves. The mind cannot possibly grasp the full meaning of
the term of a hundred million years; it cannot add up and perceive the
full effects of many slight variations, accumulated during an almost
infinite number of generations.
Although I am fully convinced of the truth of the views given in this
volume under the form of an abstract, I by no means expect to convince
experienced naturalists whose minds are stocked with a multitude of
facts all viewed, during a long course of years, from a point of view
directly opposite to mine. It is so easy to hide our ignorance under
such expressions as the "plan of creation," "unity of design," etc.,
and to think that we give an explanation when we only restate a fact.
Any one whose disposition leads him to attach more weight to
unexplained difficulties than to the explanation of a certain number
of facts will certainly reject my theory. A few naturalists, endowed
with much flexibility of mind, and who have already begun to doubt on
the immutability of species, may be influenced by this volume; but I
look with confidence to the future, to young and rising naturalists,
who will be able to view both sides of the question with impartiality.
Whoever is led to believe that species are mutable will do good
service by conscientiously expressing his conviction; for only thus
can the load of prejudice by which this subject is overwhelmed be
removed.
Several eminent naturalists have of late published their belief that a
multitude of reputed species in each genus are not real species; but
that other species are real, that is, have been independently created.
This seems to me a strange conclusion to arrive at. They admit that a
multitude of forms, which till lately they themselves thought were
special creations, and which are still thus looked at by the majority
of naturalists, and which consequently have every external
characteristic feature of true species,--they admit that these have
been produced by variation, but they refuse to extend the same view to
other and very slightly different forms. Nevertheless they do not
pretend that they can define, or even conjecture, which are the
created forms of life, and which are those produced by secondary laws.
They admit variation as a vera causa in one case, they arbitrarily
reject it in another, without assigning any distinction in the two
cases. The day will come when this will be given as a curious
illustration of the blindness of preconceived opinion. These authors
seem no more startled at a miraculous act of creation than at an
ordinary birth. But do they really believe that at innumerable periods
in the earth's history certain elemental atoms have been commanded
suddenly to flash into living tissues? Do they believe that at each
supposed act of creation one individual or many were produced? Were
all the infinitely numerous kinds of animals and plants created as
eggs or seed, or as full grown? and in the 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, etc., 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.
INDEX.
Aberrant groups, 429.
Abyssinia, plants of, 375.
Acclimatisation, 139.
Affinities:
of extinct species, 329.
of organic beings, 411.
Agassiz:
on Amblyopsis, 139.
on groups of species suddenly appearing, 302, 305.
on embryological succession, 338.
on the glacial period, 366.
on embryological characters, 418.
on the embryos of vertebrata, 439.
on parallelism of embryological development and geological succession,
449.
Algae of New Zealand, 376.
Alligators, males, fighting, 88.
Amblyopsis, blind fish, 139.
America, North:
productions allied to those of Europe, 371.
boulders and glaciers of, 373.
South, no modern formations on west coast, 290.
Ammonites, sudden extinction of, 321.
Anagallis, sterility of, 247.
Analogy of variations, 159.
Ancylus, 386.
Animals:
not domesticated from being variable, 17.
domestic, descended from several stocks, 19.
acclimatisation of, 141.
of Australia, 116.
with thicker fur in cold climates, 133.
blind, in caves, 137.
extinct, of Australia, 339.
Anomma, 240.
Antarctic islands, ancient flora of, 399.
Antirrhinum, 161.
Ants:
attending aphides, 211.
slave-making instinct, 219.
Ants, neuter, structure of, 236.
Aphides attended by ants, 211.
Aphis, development of, 442.
Apteryx, 182.
Arab horses, 35,
Aralo-Caspian Sea, 339.
Archiac, M. de, on the succession of species, 325.
Artichoke, Jerusalem, 142.
Ascension, plants of, 389.
Asclepias, pollen of, 193.
Asparagus, 359.
Aspicarpa, 417.
Asses, striped, 163.
Ateuchus, 135,
Audubon:
on habits of frigate-bird, 185.
on variation in birds'-nests, 212,
on heron eating seeds, 387.
Australia:
animals of, 116.
dogs of, 215.
extinct animals of, 339.
European plants in, 375.
Azara on flies destroying cattle, 72.
Azores, flora of, 363.
Babington, Mr., on British plants, 48.
Balancement of growth, 147.
Bamboo with hooks, 197.
Barberry, flowers of, 98.
Barrande, M. :
on Silurian colonies, 313.
on the succession of species, 325.
on parallelism of palaeozoic formations, 328.
on affinities of ancient species, 330.
Barriers, importance of, 347.
Batrachians on islands, 393.
Bats:
how structure acquired, 180.
distribution of, 394.
Bear, catching water-insects, 184.
Bee:
sting of, 202.
queen, killing rivals, 202.
Bees fertilising flowers, 73.
Bees:
hive, not sucking the red clover, 95.
cell-making instinct, 224.
humble, cells of, 225.
parasitic, 218.
Beetles:
wingless, in Madeira, 135.
with deficient tarsi, 135.
Bentham, Mr. :
on British plants, 48.
on classification, 419.
Berkeley, Mr., on seeds in salt-water, 358.
Bermuda, birds of, 391.
Birds:
acquiring fear, 212.
annually cross the Atlantic, 364.
colour of, on continents, 132.
fossil, in caves of Brazil, 339.
of Madeira, Bermuda, and Galapagos, 390.
song of males, 89.
transporting seeds, 361.
waders, 386.
wingless, 134, 182.
with traces of embryonic teeth, 451.
Bizcacha, 349.
affinities of, 429.
Bladder for swimming in fish, 190.
Blindness of cave animals, 137,
Blyth, Mr. :
on distinctness of Indian cattle, 18.
on striped Hemionus, 163.
on crossed geese, 253.
Boar, shoulder-pad of, 88.
Borrow, Mr., on the Spanish pointer, 35.
Bory St. Vincent on Batrachians, 393.
Bosquet, M., on fossil Chthamalus, 304.
Boulders, erratic, on the Azores, 363.
Branchiae, 190.
Brent, Mr. :
on house-tumblers, 214.
on hawks killing pigeons, 362.
Brewer, Dr., on American cuckoo, 217.
Britain, mammals of, 395.
Bronn on duration of specific forms, 293.
Brown, Robert, on classification, 414.
Buckman on variation in plants, 10.
Buzareingues on sterility of varieties, 270.
Cabbage, varieties of, crossed, 99.
Calceolaria, 251.
Canary-birds, sterility of hybrids, 252.
Cape de Verde islands, 398.
Cape of Good Hope, plants of, 110, 375.
Carrier-pigeons killed by hawks, 362.
Cassini on flowers of compositae, 145.
Catasetum, 424.
Cats:
with blue eyes, deaf, 12.
variation in habits of, 91.
curling tail when going to spring, 201.
Cattle:
destroying fir-trees, 71.
destroyed by flies in La Plata, 72.
breeds of, locally extinct, 111.
fertility of Indian and European breeds, 254.
Cave, inhabitants of, blind, 137.
Centres of creation, 352.
Cephalopodae, development of, 442.
Cervulus, 253.
Cetacea, teeth and hair, 144.
Ceylon, plants of, 375.
Chalk formation, 322.
Characters:
divergence of, 111.
sexual, variable, 156.
adaptive or analogical, 427.
Charlock, 76,
Checks:
to increase, 67.
mutual, 71.
Chickens, instinctive tameness of, 216.
Chthamalinae, 288.
Chthamalus, cretacean species of, 304.
Circumstances favourable:
to selection of domestic products, 40.
to natural selection, 101.
Cirripedes:
capable of crossing, 101.
carapace aborted, 148.
their ovigerous frena, 192.
fossil, 304.
larvae of, 440.
Classification, 413.
Clift, Mr., on the succession of types, 339.
Climate:
effects of, in checking increase of beings, 68.
adaptation of, to organisms, 139.
Cobites, intestine of, 190.
Cockroach, 76.
Collections, palaeontological, poor, 287.
Colour:
influenced by climate, 132.
in relation to attacks by flies, 198.
Columba livia, parent of domestic pigeons, 23.
Colymbetes, 386.
Compensation of growth, 147.
Compositae:
outer and inner florets of, 144.
male flowers of, 451.
Conclusion, general, 480.
Conditions, slight changes in, favourable to fertility, 267.
Coot, 185.
Coral:
islands, seeds drifted to, 360.
reefs, indicating movements of earth, 309.
Corn-crake, 185.
Correlation:
of growth in domestic productions, 11.
of growth, 143, 198.
Cowslip, 49.
Creation, single centres of, 352.
Crinum, 250.
Crosses, reciprocal, 258.
Crossing:
of domestic animals, importance in altering breeds, 20.
advantages of, 96.
unfavourable to selection, 102.
Crustacea of New Zealand, 376.
Crustacean, blind, 137.
Cryptocerus, 238.
Ctenomys, blind, 137.
Cuckoo, instinct of, 216.
Currants, grafts of, 262.
Currents of sea, rate of, 359.
Cuvier:
on conditions of existence, 206.
on fossil monkeys, 303.
Cuvier, Fred., on instinct, 208.
Dana, Professor:
on blind cave-animals, 139.
on relations of crustaceans of Japan, 372.
on crustaceans of New Zealand, 376.
De Candolle:
on struggle for existence, 62.
on umbelliferae, 146.
on general affinities, 430.
De Candolle, Alph.:
on low plants, widely dispersed, 406.
on widely-ranging plants being variable, 53.
on naturalisation, 115.
on winged seeds, 146.
on Alpine species suddenly becoming rare, 175.
on distribution of plants with large seeds, 360.
on vegetation of Australia, 379.
on fresh-water plants, 386.
on insular plants, 389.
Degradation of coast-rocks, 282.
Denudation:
rate of, 285.
of oldest rocks, 308.
Development of ancient forms, 336.
Devonian system, 334.
Dianthus, fertility of crosses, 256.
Dirt on feet of birds, 362.
Dispersal:
means of, 356.
during glacial period, 365.
Distribution:
geographical, 346.
means of, 356.
Disuse, effects of, under nature, 134.
Divergence of character, 111.
Division, physiological, of labour, 115.
Dogs:
hairless, with imperfect teeth, 12.
descended from several wild stocks, 18.
domestic instincts of, 213.
inherited civilisation of, 215.
fertility of breeds together, 254.
of crosses, 268,
proportions of, when young, 444.
Domestication, variation under, 7.
Downing, Mr., on fruit-trees in America, 85.
Downs, North and South, 285.
Dragon-flies, intestines of, 190.
Drift-timber, 360.
Driver-ant, 240.
Drones killed by other bees, 202.
Duck:
domestic, wings of, reduced, 11.
logger-headed, 182.
Duckweed, 385.
Dugong, affinities of, 414.
Dung-beetles with deficient tarsi, 135.
Dyticus, 386.
Earl, Mr. W., on the Malay Archipelago, 395.
Ears:
drooping, in domestic animals, 11.
rudimentary, 454.
Earth, seeds in roots of trees, 361.
Eciton, 238.
Economy of organisation, 147.
Edentata:
teeth and hair, 144.
fossil species of, 339.
Edwards, Milne:
on physiological divisions of labour, 115.
on gradations of structure, 194.
on embryological characters, 418.
Eggs, young birds escaping from, 87.
Electric organs, 192.
Elephant:
rate of increase, 64.
of glacial period, 141.
Embryology, 439.
Existence:
struggle for, 60.
conditions of, 206.
Extinction:
as bearing on natural selection, 109.
of domestic varieties, 111.
317.
Eye:
structure of, 187.
correction for aberration, 202.
Eyes reduced in moles, 137.
Fabre, M., on parasitic sphex, 218.
Falconer, Dr. :
on naturalization of plants in India, 65.
on fossil crocodile, 313.
on elephants and mastodons, 334,
and Cautley on mammals of sub-Himalayan beds, 340.
Falkland Island, wolf of, 393.
Faults, 285.
Faunas, marine, 348.
Fear, instinctive, in birds, 212.
Feet of birds, young molluscs adhering to, 385.
Fertility:
of hybrids, 249.
from slight changes in conditions, 267.
of crossed varieties, 267.
Fir-trees:
destroyed by cattle, 71.
pollen of, 203.
Fish:
flying, 182.
teleostean, sudden appearance of, 305.
eating seeds, 362, 387.
fresh-water, distribution of, 384.
Fishes:
ganoid, now confined to fresh water, 107.
electric organs of, 192.
ganoid, living in fresh water, 321.
of southern hemisphere, 376.
Flight, powers of, how acquired, 182.
Flowers:
structure of, in relation to crossing, 97.
of compositae and umbelliferae, 144.
Forbes, E. :
on colours of shells, 132.
on abrupt range of shells in depth, 175.
on poorness of palaeontological collections, 287.
on continuous succession of genera, 316.
on continental extensions, 357.
on distribution during glacial period, 366,
on parallelism in time and space, 409.
Forests, changes in, in America, 74.
Formation, Devonian, 334.
Formations:
thickness of, in Britain, 284.
intermittent, 290.
Formica rufescens, 219.
Formica sanguinea, 219.
Formica flava, neuter of, 239.
Frena, ovigerous, of cirripedes, 192.
Fresh-water productions, dispersal of, 383.
Fries on species in large genera being closely allied to other
species, 57.
Frigate-bird, 185.
Frogs on islands, 393.
Fruit-trees:
gradual improvement of, 37.
in United States, 85.
varieties of, acclimatised in United States, 142.
Fuci, crossed, 258.
Fur, thicker in cold climates, 133.
Furze, 439.
Galapagos Archipelago:
birds of, 390.
productions of, 398, 400.
Galeopithecus, 181.
Game, increase of, checked by vermin, 68.
Gartner:
on sterility of hybrids, 247, 255.
on reciprocal crosses, 258.
on crossed maize and verbascum, 270.
on comparison of hybrids and mongrels, 272.
Geese:
fertility when crossed, 253.
upland, 185.
Genealogy important in classification, 425.
Geoffrey St. Hilaire:
on balancement, 147.
on homologous organs, 434.
Geoffrey St. Hilaire, Isidore:
on variability of repeated parts, 149.
on correlation in monstrosities, 11.
on correlation, 144.
on variable parts being often monstrous, 155.
Geographical distribution, 346.
Geography, ancient, 487.
Geology:
future progress of, 487.
imperfection of the record, 279.
Giraffe, tail of, 195.
Glacial period, 365.
Gmelin on distribution, 365.
Gnathodon, fossil, 368.
Godwin-Austen, Mr., on the Malay Archipelago, 299.
Goethe on compensation of growth, 147.
Gooseberry, grafts of, 262.
Gould, Dr. A., on land-shells, 397.
Gould, Mr.:
on colours of birds, 132.
on birds of the Galapagos, 398.
on distribution of genera of birds, 404.
Gourds, crossed, 270.
Grafts, capacity of, 261.
Grasses, varieties of, 113.
Gray, Dr. Asa:
on trees of United States, 100.
on naturalised plants in the United States, 115.
on rarity of intermediate varieties, 176.
on Alpine plants, 365.
Gray, Dr. J. E., on striped mule, 165.
Grebe, 185.
Groups, aberrant, 429.
Grouse:
colours of, 84.
red, a doubtful species, 49.
Growth:
compensation of, 147.
correlation of, in domestic products, 11.
correlation of, 143.
Habit:
effect of, under domestication, 11.
effect of, under nature, 134.
diversified, of same species, 183.
Hair and teeth, correlated, 144.
Harcourt, Mr. E. V., on the birds of Madeira, 391.
Hartung, M., on boulders in the Azores, 363.
Hazel-nuts, 359.
Hearne on habits of bears, 184.
Heath, changes in vegetation, 72,
Heer, O., on plants of Madeira, 107.
Helix pomatia, 397.
Helosciadium, 359.
Hemionus, striped, 163.
Herbert, W. :
on struggle for existence, 62.
on sterility of hybrids, 249.
Hermaphrodites crossing, 96.
Heron eating seed, 387.
Heron, Sir R., on peacocks, 89.
Heusinger on white animals not poisoned by certain plants, 12.
Hewitt, Mr., on sterility of first crosses. 264.
Himalaya:
glaciers of, 373.
plants of, 375.
Hippeastrum, 250.
Holly-trees, sexes of, 93.
Hollyhock, varieties of, crossed, 271.
Hooker, Dr., on trees of New Zealand, 100.
Hooker, Dr. :
on acclimatisation of Himalayan trees, 140.
on flowers of umbelliferae, 145.
on glaciers of Himalaya, 373.
on algae of New Zealand, 376.
on vegetation at the base of the Himalaya, 378.
on plants of Tierra del Fuego, 374, 378.
on Australian plants, 375, 399.
on relations of flora of South America, 379.
on flora of the Antarctic lands, 381, 399.
on the plants of the Galapagos, 391, 398.
Hooks:
on bamboos, 197.
to seeds on islands, 392.
Horner, Mr., on the antiquity of Egyptians, 18.
Horns, rudimentary, 454.
Horse, fossil, in La Plata, 318.
Horses:
destroyed by flies in La Plata, 72.
striped, 163.
proportions of, when young, 445.
Horticulturists, selection applied by, 32.
Huber on cells of bees, 230.
Huber, P.:
on reason blended with instinct, 208.
on habitual nature of instincts, 208.
on slave making ants, 219.
on Melipona domestica, 225.
Humble-bees, cells of, 225.
Hunter, J., on secondary sexual characters, 150.
Hutton, Captain, on crossed geese, 253.
Huxley, Professor:
on structure of hermaphrodites, 101.
on embryological succession, 338.
on homologous organs, 438.
on the development of aphis, 442.
Hybrids and mongrels compared, 272.
Hybridism, 245.
Hydra, structure of, 190.
Ibla, 148.
Icebergs transporting seeds, 363.
Increase, rate of, 63.
Individuals:
numbers favourable to selection, 102.
many, whether simultaneously created, 356.
Inheritance:
laws of, 12.
at corresponding ages, 14, 86.
Insects:
colour of, fitted for habitations, 84.
sea-side, colours of, 132.
blind, in caves, 138.
luminous, 193.
neuter, 236.
Instinct, 207.
Instincts, domestic, 213.
Intercrossing, advantages of, 96.
Islands, oceanic, 388.
Isolation favourable to selection, 104.
Japan, productions of, 372.
Java, plants of, 375.
Jones, Mr. J. M., on the birds of Bermuda, 391.
Jussieu on classification, 417.
Kentucky, caves of, 137.
Kerguelen-land, flora of, 381, 399.
Kidney-bean, acclimatisation of, 142.
Kidneys of birds, 144.
Kirby on tarsi deficient in beetles, 135.
Knight, Andrew, on cause of variation, 7.
Kolreuter:
on the barberry, 98.
on sterility of hybrids, 247.
on reciprocal crosses, 258.
on crossed varieties of nicotiana, 271.
on crossing male and hermaphrodite flowers, 451.
Lamarck on adaptive characters, 427.
Land-shells:
distribution of, 397.
of Madeira, naturalised, 402.
Languages, classification of, 422.
Lapse, great, of time, 282.
Larvae, 440.
Laurel, nectar secreted by the leaves, 92.
Laws of variation, 131.
Leech, varieties of, 76.
Leguminosae, nectar secreted by glands, 92.
Lepidosiren, 107, 330.
Life, struggle for, 60.
Lingula, Silurian, 306.
Linnaeus, aphorism of, 413.
Lion:
mane of, 88.
young of, striped, 439.
Lobelia fulgens, 73, 98,
Lobelia, sterility of crosses, 250.
Loess of the Rhine, 384.
Lowness of structure connected with variability, 149.
Lowness, related to wide distribution, 406.
Lubbock, Mr., on the nerves of coccus, 46.
Lucas, Dr. P.:
on inheritance, 12.
on resemblance of child to parent, 275.
Lund and Clausen on fossils of Brazil, 339.
Lyell, Sir C.:
on the struggle for existence, 62.
on modern changes of the earth, 95.
on measure of denudation, 283.
on a carboniferous land-shell, 289.
on fossil whales, 303.
on strata beneath Silurian system, 307.
on the imperfection of the geological record, 310.
on the appearance of species, 312.
on Barrande's colonies, 313.
on tertiary formations of Europe and North America, 323.
on parallelism of tertiary formations, 328.
on transport of seeds by icebergs, 363.
on great alternations of climate, 382.
on the distribution of fresh-water shells, 385.
on land-shells of Madeira, 402.
Lyell and Dawson on fossilized trees in Nova Scotia, 296.
Macleay on analogical characters, 427.
Madeira:
plants of, 107.
beetles of, wingless, 135.
fossil land-shells of, 339.
birds of, 390.
Magpie tame in Norway, 212.
Maize, crossed, 270.
Malay Archipelago:
compared with Europe, 299.
mammals of, 395.
Malpighiaceae, 417.
Mammae, rudimentary, 451.
Mammals:
fossil, in secondary formation, 303.
insular, 393.
Man, origin of races of, 199.
Manatee, rudimentary nails of, 454.
Marsupials:
of Australia, 116.
fossil species of, 339.
Martens, M., experiment on seeds, 360.
Martin, Mr. W. C., on striped mules, 165.
Matteuchi on the electric organs of rays, 193.
Matthiola, reciprocal crosses of, 258.
Means of dispersal, 356.
Melipona domestica, 225.
Metamorphism of oldest rocks 308.
Mice:
destroying bees, 74.
acclimatisation of, 141.
Migration, bears on first appearance of fossils, 296.
Miller, Professor, on the cells of bees, 226.
Mirabilis, crosses of, 258.
Missel-thrush, 76.
Misseltoe, complex relations of, 3.
Mississippi, rate of deposition at mouth, 284.
Mocking-thrush of the Galapagos, 402.
Modification of species, how far applicable, 483.
Moles, blind, 137.
Mongrels:
fertility and sterility of, 267.
and hybrids compared, 272.
Monkeys, fossil, 303,
Monocanthus, 424.
Mons, Van, on the origin of fruit-trees, 29, 39.
Moquin-Tandon on sea-side plants, 132.
Morphology, 434.
Mozart, musical powers of, 209.
Mud, seeds in, 386.
Mules, striped, 165.
Muller, Dr. F., on Alpine Australian plants, 375.
Murchison, Sir R.:
on the formations of Russia, 289.
on azoic formations, 307.
on extinction, 317.
Mustela vison, 179.
Myanthus, 424.
Myrmecocystus, 238.
Myrmica, eyes of, 240.
Nails, rudimentary, 453.
Natural history:
future progress of, 484.
selection, 80.
system, 413.
Naturalisation:
of forms distinct from the indigenous species, 115.
in New Zealand, 201.
Nautilus, Silurian, 306.
Nectar of plants, 92.
Nectaries, how formed, 92.
Nelumbium luteum, 387.
Nests, variation in, 212.
Neuter insects, 236.
Newman, Mr., on humble-bees, 74.
New Zealand:
productions of, not perfect, 201.
naturalised products of, 337.
fossil birds of, 339.
glacial action in, 373,
crustaceans of, 376.
algae of, 376.
number of plants of, 389.
flora of, 399.
Nicotiana:
crossed varieties of, 271.
certain species very sterile, 257.
Noble, Mr., on fertility of Rhododendron, 251.
Nodules, phosphatic, in azoic rocks, 307,
Oak, varieties of, 50.
Onites apelles, 135.
Orchis, pollen of, 193,
Organs:
of extreme perfection, 186,
electric, of fishes, 192.
of little importance, 194.
homologous, 434.
rudiments of, 450.
Ornithorhynchus, 107, 416.
Ostrich:
not capable of flight, 134.
habit of laying eggs together, 218.
American, two species of, 349.
Otter, habits of, how acquired, 179.
Ouzel, water, 185.
Owen, Professor:
on birds not flying, 134.
on vegetative repetition, 149.
on variable length of arms in ourang-outang, 150.
on the swim-bladder of fishes, 191.
on electric organs, 192.
on fossil horse of La Plata, 319.
on relations of ruminants and pachyderms, 329.
on fossil birds of New Zealand, 339.
on succession of types, 339.
on affinities of the dugong, 414.
on homologous organs, 435.
on the metamorphosis of cephalopods and spiders, 442.
Pacific Ocean, faunas of, 348.
Paley on no organ formed to give pain, 201.
Pallas on the fertility of the wild stocks of domestic animals, 253.
Paraguay, cattle destroyed by flies, 72.
Parasites, 217.
Partridge, dirt on feet, 362.
Parts:
greatly developed, variable, 150.
degrees of utility of, 201.
Parus major, 183.
Passiflora, 251.
Peaches in United States, 85.
Pear, grafts of, 261.
Pelargonium:
flowers of, 145.
sterility of, 251.
Pelvis of women, 144,
Peloria, 145.
Period, glacial, 365.
Petrels, habits of, 184.
Phasianus, fertility of hybrids, 253.
Pheasant, young, wild, 216.
Philippi on tertiary species in Sicily, 312.
Pictet, Professor:
on groups of species suddenly appearing, 302, 305.
on rate of organic change, 313.
on continuous succession of genera, 316.
on close alliance of fossils in consecutive formations, 335.
on embryological succession, 338.
Pierce, Mr., on varieties of wolves, 91.
Pigeons:
with feathered feet and skin between toes, 12.
breeds described, and origin of, 20.
breeds of, how produced, 39, 42.
tumbler, not being able to get out of egg, 87.
reverting to blue colour, 160.
instinct of tumbling, 214.
carriers, killed by hawks, 362.
young of, 445.
Pistil, rudimentary, 451.
Plants:
poisonous, not affecting certain coloured animals, 12.
selection applied to, 32.
gradual improvement of, 37.
not improved in barbarous countries, 38.
destroyed by insects, 67.
in midst of range, have to struggle with other plants, 77.
nectar of, 92,
fleshy, on sea-shores, 132.
fresh-water, distribution of, 386.
low in scale, widely distributed, 406.
Plumage, laws of change in sexes of birds, 89.
Plums in the United States, 85.
Pointer dog:
origin of, 35.
habits of, 213.
Poison not affecting certain coloured animals, 12.
Poison, similar effect of, on animals and plants, 484.
Pollen of fir-trees, 203,
Poole, Col., on striped hemionus, 163.
Potamogeton, 387.
Prestwich, Mr., on English and French eocene formations, 328.
Primrose, 49.
sterility of, 247.
Primula, varieties of, 49.
Proteolepas, 148.
Proteus, 139.
Psychology, future progress of, 488.
Quagga, striped, 165.
Quince, grafts of, 261.
Rabbit, disposition of young, 215.
Races, domestic, characters of, 16.
Race-horses:
Arab, 35.
English, 356.
Ramond on plants of Pyrenees, 368.
Ramsay, Professor:
on thickness of the British formations, 284.
on faults, 285.
Ratio of increase, 63.
Rats:
supplanting each other, 76.
acclimatisation of, 141.
blind in cave, 137.
Rattle-snake, 201.
Reason and instinct, 208.
Recapitulation, general, 459.
Reciprocity of crosses, 258.
Record, geological, imperfect, 279.
Rengger on flies destroying cattle, 72.
Reproduction, rate of, 63.
Resemblance to parents in mongrels and hybrids, 273.
Reversion:
law of inheritance, 14.
in pigeons to blue colour, 160.
Rhododendron, sterility of, 251.
Richard, Professor, on Aspicarpa, 417.
Richardson, Sir J.:
on structure of squirrels, 180.
on fishes of the southern hemisphere, 376.
Robinia, grafts of, 262.
Rodents, blind, 137.
Rudimentary organs, 450.
Rudiments important for classification, 416.
Sageret on grafts, 262.
Salmons, males fighting, and hooked jaws of, 88.
Salt-water, how far injurious to seeds, 358.
Saurophagus sulphuratus, 183.
Schiodte on blind insects, 138.
Schlegel on snakes, 144
Sea-water, how far injurious to seeds, 358.
Sebright, Sir J.:
on crossed animals, 20.
on selection of pigeons, 31.
Sedgwick, Professor, on groups of species suddenly appearing, 302.
Seedlings destroyed by insects, 67.
Seeds:
nutriment in, 77.
winged, 146.
power of resisting salt-water, 358.
in crops and intestines of birds, 361.
eaten by fish, 362, 387.
in mud, 386.
hooked, on islands, 392.
Selection:
of domestic products, 29.
principle not of recent origin, 33.
unconscious, 34.
natural, 80.
sexual, 87.
natural, circumstances favourable to, 101,
Sexes, relations of, 87.
Sexual:
characters variable, 156.
selection, 87.
Sheep:
Merino, their selection, 31.
two sub-breeds unintentionally produced, 36.
mountain, varieties of, 76.
Shells:
colours of, 132.
littoral, seldom embedded, 288.
fresh-water, dispersal of, 385.
of Madeira, 391,
land, distribution of, 397.
Silene, fertility of crosses, 257.
Silliman, Professor, on blind rat, 137.
Skulls of young mammals, 197, 437.
Slave-making instinct, 219.
Smith, Col. Hamilton, on striped horses, 164.
Smith, Mr. Fred.:
on slave-making ants, 219.
on neuter ants, 239.
Smith, Mr., of Jordan Hill, on the degradation of coast-rocks, 283.
Snap-dragon, 161.
Somerville, Lord, on selection of sheep, 31.
Sorbus, grafts of, 262.
Spaniel, King Charles's breed, 35.
Species:
polymorphic, 46.
common, variable, 53.
in large genera variable, 54.
groups of, suddenly appearing, 302, 306.
beneath Silurian formations, 306.
successively appearing, 312.
changing simultaneously throughout the world, 322.
Spencer, Lord, on increase in size of cattle, 35.
Sphex, parasitic, 218.
Spiders, development of, 442.
Spitz-dog crossed with fox, 268.
Sports in plants, 9.
Sprengel, C. C.:
on crossing, 98.
on ray-florets, 145.
Squirrels, gradations in structure, 180.
Staffordshire, heath, changes in, 72.
Stag-beetles, fighting, 88.
Sterility:
from changed conditions of life, 9.
of hybrids, 246.
laws of, 254.
causes of, 263.
from unfavourable conditions, 265.
of certain varieties, 269.
St. Helena, productions of, 389.
St. Hilaire, Aug., on classification, 418.
St. John, Mr., on habits of cats, 91.
Sting of bee, 202.
Stocks, aboriginal, of domestic animals, 18,
Strata, thickness of, in Britain, 284.
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