Charles Darwin's Origins of Species outlined |
|
We found this faithful rendition of Charles Darwin's book. But, Christians must read Darwin's book in whole in order to refute it. Although we have an outline don't let that substitute your studies on Origins of Species.
The Argument of the Origin of
Species
The Origin of Species is Darwin's
best-known book and is widely available in modern reprints.
It should be noted, however, that in response to numerous
criticisms Darwin undertook constant revisions between the
book's first appearance in 1859 and the sixth edition of
1872. The later editions thus differ considerably from the
first, and the last edition contains an additional chapter
(chapter 7) dealing with objections to the theory. These
changes tend to obscure the original argument and the first
edition is thus by far the clearest expression of Darwin's
insight. A facsimile of this edition is available and also a
concordance, although many modern reprints unfortunately
follow the text of the sixth edition. All references below
are to the first edition unless otherwise stated.
|
Introduction: This leads the reader directly to
the question of adaptation which Darwin sees as the central
problem of evolution. He argues briefly that Lamarckism
cannot explain all cases of adaptation and points out that
the simple progressionism of the Vestiges does not
even address the question of how species become adapted to
their environment. From the start Darwin makes it clear that
he will be offering a new mechanism to explain the origin of
species by adaptation,
|
The main text of the Origin of Species can be
divided into three parts:
|
|
Chapters 1-5 outline the theory of natural selection,
|
|
Chapters 6-9 (6-10 in the sixth edition) deal with the
many objections that Darwin foresees will be raised against
his theory, and
|
|
the concluding chapters (10-14 in the first edition,
11-15 in the sixth) show how a wide range of otherwise
inexplicable phenomena can be illuminated by the theory of
common descent by adaptive modification.
|
I.
|
Chapters 1-5: outline the theory of natural selection
|
|
Chp1: Variation under Domestication: Chapter 1
begins by stressing that animal and plant breeders have been
able to produce immense changes within domesticated species.
Darwin was convinced that the analogy with artificial
selection was the best way of helping his readers to
understand how nature might be able to produce similar
changes by an equivalent selective process. Almost
immediately we encounter Darwin's pre-Mendelian theory of
variation and inheritance. Like the notebooks of the 1830s,
the Origin of Species is pervaded by a way of
thinking about reproduction which is quite alien to modern
biology. There is no direct equivalent of the modern belief
that the population contains a reservoir of genetic
variability, each gene being transmitted as a unit from one
generation to the next. Instead, Darwin argues that
individual variation is due to the direct effect of changed
conditions on the reproductive process. This, he believes,
will explain why domesticated species exhibit more
variability than wild ones. Further details are given in
chapter 5, "Laws of Variation," where he insists that all
changes of structure are caused, even though we do
not know the cause and speak of them as being due to chance
(131-2). In this chapter Darwin admits a minor role for
Lamarckism, although he insists that most of the variability
is undirected.
In his discussion of variation under domestication,
Darwin moves from a general account of the "random"
variation in domesticated species to the work of the animal
breeders who exploit that variation to produce significant
changes. He goes to some length to show that we cannot draw
a rigid distinction between the production of new breeds
by man and the appearance of new species in
nature. Artificial breeds do not invariably tend to revert
to some fixed "natural" form for their species. The
diversity of pigeon breeds is enormous, and Darwin argues
that, if the different breeds were shown to an ornithologist
who did not know that they were domesticated, he would
classify them as belonging to distinct species, perhaps even
distinct genera. What, then, is the explanation of man's
ability to produce such enormous changes in a species? "The
key is man's power of accumulative selection: nature gives
incessant variations; man adds them up in certain directions
useful to him" (30).
|
|
Chp. 2: Variation under Nature: In chapter 2
Darwin asks whether the variation which serves as the raw
material of selection exists in wild populations. He admits
that there may be much less variation in the wild
because--according to his theory--wild species exist under
"natural" conditions which do not disturb the reproductive
process. But individual differences do occur and even the
most important structures are subject to variation, as
evidence of which Darwin cites studies by John Lubbock which
had demonstrated major variations in the patterns of the
nervous system within a single insect species. "These
individual differences are highly important for us, as they
afford materials for natural selection to accumulate, in the
same manner as man can accumulate in any given direction
individual differences in his domesticated productions"
(45).
Much of chapter 2 is devoted to a very different method
of demonstrating the variability of wild species. Darwin
points to the fact that many species are known to form
fairly distinct and permanent races or "varieties" adapted
to the local conditions in certain parts of their territory.
Naturalists had been quite willing to assume that such
varieties were formed by common descent from a single
ancestral form, yet there was often disagreement as to
whether a particular form was a variety or a distinct
species. Darwin argues that the confusion arises because
varieties are merely an intermediate step in the production
of new species: "a well-marked variety may justly be called
an incipient species" (52). The term "species" is thus an
arbitrary one: a species is just a strongly marked variety
that the majority of experienced naturalists agree to call a
species. Once this point is accepted the barriers supposedly
separating species have been broken down and the way is
cleared for transmutation to be used to explain the
production of all new forms of life.
|
|
Chp. 3: Struggle for Existence: Chapter 3
introduces this concept which arises from the tendency of
all species to over-reproduce. If more are born than can
possibly survive, there must be competition to see which
individuals will get enough of the scarce resources to keep
themselves alive. Darwin is quite clear that this idea has
its origins in the "principle of population" that Malthus
applied to human society: "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" (63). The force of this argument is based on
numerical calculations designed to show the potential rate
of population increase that must be checked by the shortage
of resources.
The struggle is most severe between members of the same
species, or between closely related varieties, because here
the individuals are competing for exactly the same
resources. Many different factors determine who shall live
and who shall die. Often the elimination takes place among
the young; sometimes shortage of food is critical but often
it is predators which keep the population down. Darwin
emphasizes the complex web of interactions between species,
each being held in check by others which prey upon it or
upon which it preys. Many readers of the Origin of
Species were impressed by his emphasis on the complex
network of living relationships even if they did not accept
the theory of natural selection. Darwin admits that behind
'the face of nature bright with gladness' there is a scene
of constant struggle. Yet he was anxious not to create too
harsh an image of nature. He wished to imply that his theory
modified, but did not challenge, the prevailing belief that
nature had been created by a wise and benevolent God. The
last thing he wanted was for people to see his book as the
basis for an amoral view of nature. He thus ends his chapter
on the struggle for existence with the following words:
|
|
|
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. (79)
|
|
Chp. 4: Natural Selection: Chapter 4 contains
Darwin's main description of his mechanism. After reminding
his readers of the power of artificial selection and of the
dependence of the wild organism on its environment, he goes
on:
|
|
|
Can it, then, be thought improbable, seeing that
variations useful to man have undoubtedly occurred, that
other variations useful in some way to each being in the
great and complex battle of life, should sometimes occur in
the course of thousands of generations? If such do occur,
can we doubt (remembering that many more individuals are
born than can possibly survive) that individuals having any
advantage, however slight, 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 variations and the rejection of
injurious variations, I call Natural Selection. (80-81)
|
|
Darwin contrasts nature's powers with those of mankind,
stressing how much more effective will be the scrutiny of
nature. He points out that natural selection acts only to
improve the organisms' ability to cope with their
environment and thus tries to persuade his readers that,
whatever the apparent harshness of natural selection, we can
nevertheless see it as a force promoting the improvement of
living things.
Reproduction rather than survival is the crucial factor
of course, a point illustrated in the section on 'Sexual
selection' in which Darwin argues that any character useful
in obtaining a mate will become highly developed. The
antlers of deer and the bright colours of many birds are
explained by the fact that the mating habits of the various
species allow those males with well-developed secondary
sexual characters to attract more females.
Darwin explains that the extinction of some forms will be
inevitable in a world governed by natural selection. Species
will often be exterminated by competitors, thus in effect
leaving room for the more successful species to multiply. At
the end of chapter 4 he includes a long discussion of the
process of divergence by which a single original form can
give rise to a family of descendants, each of which will
become more specialized for its own way of life and which
may itself subdivide. Natural selection will always favour
increased specialization even in a stable environment. He
gives a diagram to illustrate the process - a classic
example of an evolutionary tree. Significantly, Darwin's
tree has no central trunk or 'main stem' of evolution. No
one branch can be singled out as the main line of
development because each is adapting in its own way to the
environmental changes it encounters in the course of its
migrations. There is no way in which the human race can be
seen as the goal towards which the evolution of the whole
animal kingdom has been striving.
|
II.
|
Chapters 6-9 [6-10 in the sixth edition]: The
many objections that Darwin foresees will be raised against
his theory
|
|
[6]: [Miscellaneous Objections to the
Theory of Natural Selection]: The additional chapter
[6] added to the last edition includes Darwin's
response to critics who had indeed expressed and extended
the problems he had anticipated.
|
|
Chp. 6: Difficulties on Theory: With chapter 6
[7] we move into the central section of the
Origin of Species in which Darwin attempts to defend
his idea against the objections he foresees will be raised
against it.
|
|
|
1) The first problem in chapter 6 is that of the lack of
transitional forms between known species. This is an
important point because it is often assumed that a theory of
continuous evolution must imply that there are no
gaps between species. Darwin argues that this is not the
case if evolution is a branching divergent process.
Divergence takes place through the continued extermination
of the less specialized forms and thus the intermediates do
not survive through to the present. In his view, "species
come to be tolerably well-defined objects, and do not at any
one period present an inextricable chaos of varying and
intermediate links" (177).
2) The next problem is the origin of species with
peculiar habits or structures. How, for instance, could a
non-flying mammal evolve into a bat--surely the intermediate
forms would have limbs that were not well adapted either for
walking or for flying? Here Darwin appeals to the existence
of flying squirrels with varying abilities to glide from
tree to tree. These confirm that the intermediate state
between legs and wings is viable, thus illustrating the
route selection may have taken in the creation of the more
perfect wings of bats. Darwin notes that species do indeed
change their habits, as witnessed by certain kinds of
woodpeckers that do not live in trees and web-footed geese
that do not live in water. These examples are inexplicable
on the assumption that God creates every species perfectly
adapted to its way of life, but are to be expected if
species are constantly trying to find new ecological niches
to exploit and if evolution takes some time to adjust a
species to a new way of life.
3) Darwin also refers to the problem of explaining the
evolution of a highly complex structure such as the human
eye. He notes that in the invertebrates there are creatures
with eyes of varying degrees of complexity, showing that
intermediate stages in the development of vision can be of
benefit to the species. He admits that, if one could find a
complex organ for which no intermediate states were
conceivable, his theory would have to be rejected, but
insists that no such organs are known. Another problem is
the existence of organs of little apparent importance. If
natural selection works only by seizing upon advantageous
variations, then surely all characters must be adaptive. Yet
many naturalists were convinced that species possess useless
characters. Darwin responds to this problem by suggesting
that we may often underestimate a structure's usefulness.
The giraffe's tail seems to be used as a fly-flapper, which
appears rather trivial until one recollects that in some
parts of the tropics the distribution of large mammals is
critically determined by their vulnerability to insect
pests.
|
|
Chp. 7: Instinct: Chapter 7 [8] deals
with, a topic of particular interest to Darwin because he
was convinced that evolution must be able to explain animal
behaviour. The Lamarckians had an obvious explanation of
instinct as a learned habit that had gradually been built
into the species' hereditary constitution. But Darwin notes
that this will not explain the instincts of neuter insects.
He was convinced that natural selection can act on instincts
just as it can act on physical characters. There is
variation within the instinctive behaviour of any particular
species, as shown by the fact that man has been able to
eradicate the dog's instinctive tendency to attack sheep.
Thus selection will be able to enhance a useful instinct by
seizing upon useful variations. The case of neuter insects
is explained by the fact that selection can act on families
as well as individuals: insects with a tendency to produce
some useful but neuter types among their offspring would
survive better as the founders of colonies.
|
|
Chp. 8: Hybridism: In chapter 8 [9],
Darwin deals with what many critics saw as a fatal objection
to his theory. Varieties formed within the same species can
be cross-bred with one another, but on the traditional view
any attempt to hybridize distinct species will always fail.
Darwin counters this argument by showing that the supposed
absolute distinction between varieties and species is not as
clear-cut as was popularly supposed. He cites extensive
evidence to show that varying degrees of sterility are
encountered in efforts to cross-breed different species of
plants. If the species are closely related, there will often
be a small degree of fertility in the hybrid offspring. His
conclusion is that, far from being a fatal objection to his
theory, a close study of hybridization confirms that there
is no sharp distinction between varieties and species. As
two related forms diverge further from one another in the
course of evolution, their ability to interbreed gradually
diminishes and eventually falls to zero, that is, absolute
sterility.
|
|
Chp. 9: On the Imperfection of the Geological Record:
In Chapter 9 Darwin anticipates objections to his
commitment to the belief that evolution always takes place
slowly and gradually. He was aware that this did not seem to
be supported by the fossil record which generally shows new
species appearing abruptly with no sign of an evolutionary
ancestry. He argues that the discontinuity is a result of
the record's imperfection and not an indication that species
really are introduced suddenly. He points out (280) that it
would be a mistake to look for simple intermediates between
two related forms; they will have diverged from a common
ancestor that would not have been an exact intermediate
between its later descendants. But even this more complex
kind of relationship is seldom found in the record, and
Darwin insists that we should not expect to find all the
steps in evolution preserved in the rocks. Fossilbearing
rocks are only laid down in certain circumstances, and thus
long periods of time will have passed between the deposition
of strata that now seem consecutive. Even when we have a
continuous sequence of depositions, evolutionary changes may
often have taken place in isolated parts of a species' range
where fossils are not being laid down (a point amplified in
the modern theory of punctuated equilibrium).
A related problem concerns the abrupt appearance of whole
groups of living things at certain points in the record. The
most obvious example of this is what we now know as the
"Cambrian explosion" the sudden appearance of all the basic
modern types at the beginning of the Cambrian era. (Note
that in the first edition Darwin places this in the
Silurian--the geological nomenclature was disputed at the
time.) Darwin argues that the imperfection of the record
also accounts for these episodes. There must have been vast
periods of time before the Cambrian when life was evolving
but from which so far no fossils had been found. Perhaps the
continents were positioned differently so long ago, and most
of the fossil-bearing rocks from that age are sunk beneath
the modern oceans. All that Darwin could do was to express
the hope that some fossils from the pre-Cambrian rocks would
eventuall~, be found to fill in the gap.
|
III.
|
Chapters 10-14 [11-15]: a wide range of otherwise
inexplicable phenomena can be illuminated by the theory of
common descent by adaptive modification.
|
|
Chp. 10: On the Geological Succession of Organic
Beings: Chapter 10 [11] continues the discussion
of the fossil record but Darwin now moves onto the offensive
so that his concluding chapters can present the positive
case for evolution. Here he argues that, if we make
allowances for the imperfection of the record, the known
fossils are distributed just as one would expect on the
basis of a theory of common descent. Palaeontologists were
generally agreed that in any sequence of fossil formations
the intermediate forms in time were intermediate in
character. Owen and others had also shown that ancient types
often seemed to 'fall between' the more distinct modern
forms. Thus the pigs and camels could now be united into a
single group by including fossils which were intermediate in
character. To Darwin it was obvious that these ancient types
were the generalized ancestors from which the more
specialized modern forms had evolved.
|
|
Chp. 11: Geographic Distribution: This and the
next chapter deal some of the evidence that converted Darwin
himself to a belief in evolution. In Chapter 11 Darwin
insists that the differences between the Old and New World
faunas cannot be explained in terms of climate since both
areas share the same range of physical conditions. The
ostrich of Africa and the rhea of South America are
superficially similar, but when examined carefully each is
seen to be characteristic of its own continent. The chief
determinant of geographical distribution is the barriers
which exist to free migration, of which the oceans are the
most important in the case of land animals. Conversely, dry
land creates an obvious barrier to the migration of marine
forms. Darwin argues that a successful species will spread
out as far as it can, adapting to the local conditions it
encounters, until it meets an impassable barrier. Thus on
his theory it is to be expected that major barriers to
migration will define unique groups of species.
|
|
Chp. 12: Geographic Distribution (Continued): In
Chapter 12 Darwin also discusses the process by which
oceanic islands such as the Galapagos are populated,
bringing in his own studies of how seeds and eggs can
occasionally be transported across wide stretches of
ocean.
|
|
Chp. 13: Mutual Affinities of Organic Beings:
Chapter 13 allows Darwin to develop the explanatory
power of his theory to the full. He picks out a number of
phenomena encountered by naturalists in their efforts to
classify species and demonstrates that they are explicable
only in terms of a theory of common descent. The basic
system of classification entails the grouping of similar
species into genera, the genera themselves into families and
so on. By uncovering these relationships naturalists were
seeking what was called a 'Natural System' of classification
- but Darwin now asks what this system is supposed to be. Is
it the plan of the Creator, as many exponents of natural
theology liked to claim? Darwin insists that to assume the
existence of an underlying divine plan adds nothing to our
knowledge of natural relationships. His theory alone can
explain why species are grouped together: the natural system
is an expression of evolutionary relationships, in effect a
cross-section of the evolutionary tree.
Darwin next turns to embryology, noting that the embryos
of different animals often show a much greater degree of
resemblance than the adults. This, he believes, can be
explained on the assumption that adaptive modifications are
produced mostly by changes in the later stages of growth,
leaving the early pattern of development unchanged. For
Darwin, the embryo represents the species in a less modified
state and thus helps to reveal its natural relationships. In
some cases the embryo may actually resemble ancestral forms
that can be discovered in the fossil record (449-50). But
this is a far cry from the so-called, 'recapitulation
theory' in which the development of the human embryo is
supposed to repeat the whole pattern of evolution revealed
by the fossil record. Darwin had no interest in the idea of
a linear pattern of development leading up to mankind as the
goal of creation, and hence no interest in using the growth
of the human embryo as a model for the "main line" of
evolution.
Finally, Darwin turns to the topic of rudimentary or
atrophied organs. Many species have such organs, which are
of no apparent use and which often never develop beyond a
vestigial stage. Creationists must explain such structures
as necessary "for the sake of symmetry' or ,to complete the
scheme of nature," but Darwin once again insists that to
invoke a divine plan of nature is no explanation at all. The
evolutionist has an obvious explanation since he can show
that the rudimentary organs are relics of once useful
structures, now declining because the changing habits of the
species have rendered them superfluous. Heredity preserves
the structure to some extent but it gradually decays because
natural selection will favor those individuals who do not
waste their energy growing useless structures.
|
|
Chp. 14: Recapitulation and Conclusions: In
chapter 14 Darwin sums up the general implications of his
new approach. He looks to the younger generation of
naturalists in the hope that they will be able to throw off
the prejudices that commit many experienced workers to
creationism. He now reveals how far he is prepared to extend
his theory. The basic similarities between all living things
lead him to infer that "all the organic beings which have
ever lived on this earth have descended from some one
primordial form, into which life was first breathed" (484).
The latter phrase seems to imply that the original creation
of life was by divine miracle. It is not at all clear that
Darwin really believed this, but he knew that biologists
such as Pasteur had demolished the claim that life was now
being produced by spontaneous generation. Perhaps conditions
were different in the early periods of the earth's history,
but Darwin had no interest in trying to explore the ultimate
origins of life. Spontaneous generation was seen as an
inherently materialistic hypothesis and he thus felt it
safer to leave open the possibility of a supernatural
origin.
Darwin expresses the hope that evolutionism will bring
about a revolution in natural history as scientists begin to
explore the theory's applications. In particular he notes
that "Light will be thrown on the origin of man and his
history" (488). This is not the only reference to changes
within the human race in the Origin of Species,
but it is the only absolutely unequivocal statement of
Darwin's belief that his theory will account for the origins
of mankind from a lower form. He was well aware that the
extension of the theory to mankind would provoke controversy
because it would threaten the traditional view that our
mental powers lift us onto a higher plane than the animals.
He hoped to minimize the resulting outcry by refusing to
discuss human origins in detail but felt that he had to
include at least this brief indication of his beliefs.
To offset this dangerous implication, Darwin concludes
with an effort to convince his readers that the theory can
be reconciled with traditional beliefs about the
relationship between God and nature. He argues that it is
better to think of the Creator governing the world by law
rather than by arbitrary miracles and suggests that 'as
natural selection works solely by and for the good of each
being, all corporeal and mental endowments will tend to
progress towards perfection' (488-9)
There can be no direct trend leading towards mankind, but
we can be sure that the overall effect of natural selection
is progressive and hence that the human race is the outcome
of a process established by its Creator. Natural selection
follows inevitably from the laws of reproduction and is thus
the best way for God to ensure progress in so complex a
world.
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. (490)
|
-------------------------------------------------------------------------------------
Home
|
|
|
|
|