Darwin

1
Darwins book Darwin had been working for several
years on his major species book, but was still
years away from finishing it. On July 20, 1858,
he decided to write an abstract of this work for
quicker publication, to be called An Abstract of
an Essay on the Origin of Species and Varieties
Through Natural Selection, a title the publisher
(John Murray) rightly considered too clunky. The
full title of the book in its first edition was
On the Origin of Species by Means of Natural
Selection, or the Preservation of Favoured Races
in the Struggle for Life, but by the sixth
edition this had been shortened to just The
Origin of Species.
2
Title Page of the First Edition of On the Origin
of Species. Races in the long subtitle (typical
of Victorian books) had the meaning of
varieties and not the modern meaning. The
first use of races in the book is a reference
to races of cabbage. Darwin is identified as
the author of his journal about the voyage of the
Beagle.
3
Review of On the Origin of Species On December
26, 1859, a very favorable review of Darwins
book appeared in the Times of London. The Times
was a very conventional, very orthodox newspaper
(satirized by Anthony Trollope as Jupiter
Olympus the voice of the gods), which ran only
one or two book reviews a month, and it made no
sense that if they reviewed On the Origin of
Species they would not severely attack it.
Darwin was greatly surprised, and wondered who
had written it. The review sounded to him as
though it had been written by Huxley, but it was
inconceivable, given Huxleys reputation, that
they would ever ask him to write for them. Darwin
wrote to Huxley about the review .
4
The author is a literary man German scholar.
He has read my book attentively but what is very
remarkable, it seems that he is a profound
naturalist. He knows my Barnacle book,
appreciates it too highly. Lastly he writes
thinks with uncommon force clearness what is
even still rarer his writing is seasoned with
most pleasant wit Who can it be? Certainly I
should have said that there was only one man in
England who could have written this essay that
you were the man. But I suppose that I am wrong,
that there is some hidden genius of great
calibre. For how could you influence Jupiter
Olympus make him give 3 ½ columns to pure
science. The old Fogies will think the world
will come to an end. Well whoever the man is,
he has done great service to the cause, far more
than by a dozen reviews in common periodicals.
If you should happen to be acquainted with the
author for Heaven-sake tell me who he is.
5

• 5 Separate Theses of Darwins Views of Evolution
• These are the major theses of what has often been
  called Darwinism.
• Evolution as such. This is the thesis that the
  world is not constant or recently created nor
  perpetually cycling but rather is steadily
  changing and that organisms are transformed in
  time.
• (2) Common descent
• (3) Multiplication of species
• (4) Gradualism
• (5) Natural selection

6
Examples A common ancestor of chimpanzees and
bonobos (formerly pygmy chimpanzees or hippie
chimpanzees) split into these two lines several
million years ago. A common ancestor of
chimpanzees, bonobos, and humans split about 5 to
7 million years ago. Many splits seem to have
occurred on the hominid line, with only one
species remaining today, Homo sapiens. The apple
maggot (Rhagoletis pomonella) originally fed on
hawthorn apples, but in North America has split
since 1800 into two species, one feeding on
hawthorns and one on apples, which the maggot
also found palatable.
7
(1) Evolution as such (2) Common descent. This
is the thesis that every group of organisms
descended from a common ancestor and that all
groups of organisms, including animals, plants,
and microorganisms, ultimately go back to a
single origin of life on earth. (3)
Multiplication of species (4) Gradualism (5)
Natural selection
8
The Fundamental Tree of Life
9
(1) Evolution as such (2) Common descent (3)
Multiplication of species. This thesis explains
the origin of the enormous organic diversity. It
postulates that species multiply, either by
splitting into daughter species or by
budding, that is, by the establishment of
geographically isolated founder populations that
evolve to new species. (4) Gradualism (5)
Natural selection
10
Humans and their nearest relatives
11

• Evolution as such
• Common descent
• (3) Multiplication of species
• (4) Gradualism. According to this thesis,
  evolutionary change takes place through the
  gradual change of populations and not by the
  sudden (saltational) production of new
  individuals that represent a new type. Many of
  the older Darwinians, including Huxley,
  preferred saltation for one thing, it was
  thought that the Earth was not old enough for
  such gradual processes to have occurred.
• (5) Natural selection

12
(1) Evolution as such (2) Common descent
(3) Multiplication of species (4)
Gradualism (5) Natural selection. According to
this thesis, evolutionary change comes about
through the abundant production of genetic
variation in every generation. The relatively
few individuals who survive, owing to a
particularly well-adapted combination of
inheritable characters, give rise to the next
generation.
13
The Natural Selection Argument Fact 1. Every
population has such high fertility that its size
would increase exponentially if not constrained.
This was pointed out by both William Paley and
Thomas Malthus, and is clear from our own
observations of plants and animals. Think of a
single tomato plant, and all the tomatoes it
produces, and all the seeds in each tomato.
Think of a pine tree, and all the pine cones it
produces each year, all the seeds on each cone,
and all the new pine tree seedlings that can
result therefrom or think of a redbud tree, or
a maple tree, or almost any kind of weed. Think
of a queen honeybee and all the bees it can give
birth to each year. Think of all the children a
human female could give birth to in her lifetime.
14
(No Transcript)
15
Fact 2. The size of populations, except for
temporary annual fluctuations, remains stable
over time (observed steady-state stability).
This we see from our own observations again. A
gardener who plants a few tomato plants one year
doesnt necessarily find thousands of tomato
plants in the garden the next year. A homeowner
with a prolific crabapple tree doesnt find tens
of thousands of crabapple seedlings on his
property the next year (or at least, will get rid
of most of them!). Rabbits breed quickly dont
usually multiply as wildly as they could, in
principle.
16
Fact 3. The resources available to every species
are limited. This point was made by Malthus, but
is evident from our own observations, whether we
are talking about plants or animals. Inference
1. There is intense competition (struggle for
existence) among the members of a species. This
point was made by Malthus with regard to human
populations, de Candolle with regard to all
organisms. It is most evident for animals, but
is also true for plants and bacteria.
17
Fact 4. No two individuals of a population are
exactly the same (population thinking). (This
was evident to animal breeders, who deliberately
chose the best specimens to propagate, to
horticulturists, for the same reason, and, in
general, to all taxonomists but not generally
appreciated by non-scientists.) Inference 2.
Individuals of a population differ from each
other in the probability of survival (i.e.,
natural selection). This inference was made by
Darwin, for populations of all types of
organisms, but had previously been noted by
others, usually with respect to a particular
species or variety.
18
Fact 5. Many of the differences among the
individuals of a population are, at least in
part, heritable. This information came from
animal breeders (breeders of pigeons, livestock,
etc.) Inference 3. Natural selection, continued
over many generations, results in evolution.
This was Darwins conclusion from the five facts
and two inferences listed above. This line of
reasoning makes natural selection pretty
unavoidable and thus pretty certain. What is not
clear is how important it is in nature and at
what rate it occurs. Also, there could be other
types of selection, and Darwin identified one
sexual selection (to be discussed later).
19
Chapter Titles

• Chapter Titles in On the Origin of Species
• Variation under Domestication
• Variation under Nature
• Struggle for Existence
• Natural Selection
• Laws of Variation
• Difficulties on Theory
• Instinct
• Hybridisation
• On the Imperfection of the Geological Record
• On the Geological Succession of Organic Beings
• Geographical Distribution
• Geographical Distribution continued
• Mutual Affinities of Organic Beings Morphology
  Embryology Rudimentary Organs
• Recapitulation and Conclusion

20
Chapter 1 Variation under Domestication Darwins
first chapter discusses artificial selection
the breeding of better horses, pigeons, plants,
etc. by subjecting them to new conditions and
deliberately choosing to reproduce the best stock
or the individuals with the desired
characteristics. This was a familiar topic to
the British. Darwin argues at length that it is
not possible to distinguish between new breeds
produced by artificial human selection and the
new species produced in nature by natural
selection. Individuals of a domestic variety
differ more from one another than do individuals
in a wild species. More species occur in populous
genera than in the less populous an unusual
fact of no significance if one assumes special
creation, but understandable under the theory of
natural selection.
21
Pigeons Believing that it is always best to
study some special group, I have, after
deliberation, taken up domestic pigeons. I have
kept every breed which I could purchase or
obtain, and have been most kindly favoured with
skins from several quarters of the world, more
especially by the Honourable W. Elliot from
India, and by the Honourable C. Murray from
Persia. Many treatises in different languages
have been published on pigeons, and some of them
are very important, as being of considerable
antiquity. I have associated with several
eminent fanciers, and have been permitted to join
two of the London Pigeon Clubs.
22
The diversity of the breeds is something
astonishing. Compare the English carrier and the
short-faced tumbler, and see the wonderful
difference in their beaks, entailing
corresponding differences in their skulls. The
carrier, more especially the male bird, is also
remarkable from the wonderful development of the
carunculated skin about the head, and this is
accompanied by greatly elongated eyelids, very
large external orifices to the nostrils, and a
wide gape of mouth. The short-faced tumbler has
a beak in outline almost like that of a finch
and the common tumbler has the singular and
strictly inherited habit of flying at a great
height in a compact flock, and tumbling in the
air head over heels.
23
The runt is a bird of great size, with long,
massive beak and large feet some of the
sub-breeds of runts have very long necks, others
very long wings and tails, others singularly
short tails. The barb is allied to the carrier,
but, instead of a very long beak, has a very
short and very broad one. The pouter has a much
elongated body, wings, and legs and its
enormously developed crop, which it glories in
inflating, may well excite astonishment and even
laughter. The turbit has a very short and
conical beak, with a line of reversed feathers
down the breast and it has the habit of
continually expanding slightly the upper part of
the oesophagus.
24
The Jacobin has the feathers so much reversed
along the back of the neck that they form a hood,
and it has, proportionally to its size, much
elongated wing and tail feathers. The trumpeter
and laugher, as their names express, utter a very
different coo from the other breeds. The fantail
has thirty or even forty tail-feathers, instead
of twelve or fourteen, the normal number in all
members of the great pigeon family and these
feathers are kept expanded, and are carried so
erect that in good birds the head and tail touch
the oil-gland is quite aborted. Several other
less distinct breeds might have been specified.
25
Variability of pigeons A carrier pigeon and a
pouter pigeon
26
Chapter 1 continued Darwin, who had discussed
pigeons with many pigeon-breeders, described
their immense variability, but concluded that
Great as are the differences between the breeds
of the pigeon, I am fully convinced that all are
descended from the rock-pigeon Columba livia.
Pigeon breeders, who thought they were just
perfecting each breed, did not believe Darwin.
Columba livia The wild rock-pigeon or rock-dove.
27
Variations in domestic fowl Hamburg fowl (upper
left) Spanish fowl (upper right) Polish fowl
(bottom)
28
Chapter 2 Variation under Nature In Chapter 2,
Darwin showed that animal and plant populations
in the wild exhibit considerable variation. Some
variations (like monstrosities and variations due
to the environment) are not inheritable, but
others are, and slight variations can build up
into large differences. Darwin stated that
variations could exist between varieties in a
species and between species, but the distinction
between species and varieties is difficult to
ascertain and probably not meaningful. This was
proved by the fact that botanists and zoologists
often disagreed in classifying different
organisms as members of different species or
members of different varieties few well-marked
and well-known varieties can be named which have
not been ranked as species by at least some
competent judges.
29
Chapter 2 continued Darwin regarded the line
between species and varieties as somewhat
arbitrary, although variation between species
would have to be greater than variation between
varieties. But larger samples of organisms of a
species exhibited greater variation, so species
or genera that extended over greater geographical
areas would exhibit greater variation (have more
species or subspecies) than those confined to a
smaller area.
30
I look at individual differences, though of
small interest to the systematist, as of high
importance for us, as being the first step
towards such slight varieties as are barely
thought worth recording in works on natural
history. And I look at varieties which are in any
degree more distinct and permanent, as steps
leading to more strongly marked and more
permanent varieties and at these latter, as
leading to sub-species, and to species. I
attribute the passage of a variety, from a state
in which it differs very slightly from its parent
to one in which it differs more, to the action of
natural selection in accumulating (as will
hereafter be more fully explained) differences of
structure in certain definite directions. Hence I
believe a well-marked variety may be justly
called an incipient species
31
Chapter 3 Struggle for Existence This chapter
describes the constant struggle for existence in
nature. Darwin mentions Malthus as an
inspiration for this insight. Darwin describes
the constant struggle for existence among
organisms, mainly between individuals of the same
species but also to some extent between
individuals of different species. Nature itself
also puts pressure on individuals through natural
disasters, epidemics, changes in climate, etc.
Individuals with better characteristics
predominate, leading to wonderful adaptations
found in nature the woodpeckers beak that
allows it to catch insects to eat, the structure
of a parasite allowing it to attach to its host
and feed on it, the ability of a beetle to dive
underwater for food, seeds that can be carried
far away by the wind, etc. Species with larger
populations are more likely to be able to adapt
and survive by leaving more progeny.
32
Darwin points out that the struggle for existence
is easy to overlook or forget about, despite its
overwhelming importance We behold the face of
nature bright with gladness, we often see
superabundance of food we do not see, or we
forget, that the birds which are idly singing
round us mostly live on insects or seeds, and are
thus constantly destroying life or we forget how
largely these songsters, or their eggs, or their
nestlings, are destroyed by birds and beasts of
prey we do not always bear in mind, that though
food may be now superabundant, it is not so at
all seasons of each recurring year.
33
Owing to this struggle for life, any variation,
however slight and from whatever cause
proceeding, if it be in any degree profitable to
an individual of any species, in its infinitely
complex relations to other organic beings and to
external nature, will tend to the preservation of
that individual, and will generally be inherited
by its offspring. The offspring, also, will thus
have a better chance of surviving, for, of the
many individuals of any species which are
periodically born, but a small number can
survive. I have called this principle, by which
each slight variation, if useful, is preserved,
by the term of Natural Selection, in order to
mark its relation to man's power of selection.
34
Chapter 4 Natural Selection Chapter 4 fleshes
out the operation of natural selection, a
metaphorical term to suggest that nature can act
on organisms in a way that results in changes
like those of an animal breeder. Darwins
argument is based on the facts we discussed
earlier (1) Organisms produce many more
offspring than necessary just to replace the
parent organisms (2) resources to support life
are limited, leading to competition (the
struggle for existence) (3) individual
organisms have different traits, which influence
their survival and reproduction rates (4)
organisms with the best such traits leave the
most progeny, and over many generations these
traits come to predominate and may lead to new
species i.e., evolution.
35
Chapter 4 contains the only diagram in On the
Origin of Species, a tree of life diagram,
reproduced below.
36
Chapter 5 Laws of Variation This is the least
successful chapter in On the Origin of Species,
and does not contain much of value. Darwin
really doesnt know what the laws of variation
are, and he knows he doesnt, because he says,
Our ignorance of the laws of variation is
profound. Not in one case out of a hundred can we
pretend to assign any reason why this or that
part differs, more or less, from the same part in
the parents. The chapter ends Whatever the
cause may be of each slight difference in the
offspring from their parents and a cause for
each must exist it is the steady accumulation,
through natural selection, of such differences,
when beneficial to the individual, that gives
rise to all the more important modifications of
structure, by which the innumerable beings on the
face of this earth are enabled to struggle with
each other, and the best adapted to survive.
37
Chapter 6 Difficulties on Theory Darwin wanted
to answer objections to his theory before the
critics could make them. He addresses two in
this chapter. Firstly, why, if species have
descended from other species by insensibly fine
gradations, do we not everywhere see innumerable
transitional forms? Why is not all nature in
confusion instead of the species being, as we see
them, well defined? Darwin points out that as
organisms become better adapted and win in the
struggle for existence, the transitional forms
must lose and disappear. This doesnt happen
instantaneously, of course, so organisms are
usually not perfectly adapted to their way of
life. The existence of organisms that are not
perfectly adapted is not compatible with the
concept of a creator who created perfectly
adapted organisms.
38
Secondly, is it possible that an animal having,
for instance, the structure and habits of a bat,
could have been formed by the modification of
some animal with wholly different habits? Can we
believe that natural selection could produce, on
the one hand, organs of trifling importance, such
as the tail of a giraffe, which serves as a
fly-flapper, and, on the other hand, organs of
such wonderful structure, as the eye, of which we
hardly as yet fully understand the inimitable
perfection? Darwin admitted he could not give
complete answers to any specific questions of
this sort, but that with greater knowledge of
present and former organisms the evolution of
such traits and organs would be understood.
39
To suppose that the eye, with all its inimitable
contrivances for adjusting the focus to different
distances, for admitting different amounts of
light, and for the correction of spherical and
chromatic aberration, could have been formed by
natural selection, seems, I freely confess,
absurd in the highest possible degree. Yet reason
tells me, that if numerous gradations from a
perfect and complex eye to one very imperfect and
simple, each grade being useful to its possessor,
can be shown to exist if further, the eye does
vary ever so slightly, and the variations be
inherited, which is certainly the case and if
any variation or modification in the organ be
ever useful to an animal under changing
conditions of life, then the difficulty of
believing that a perfect and complex eye could be
formed by natural selection, though insuperable
by our imagination, can hardly be considered
real.
40
Darwin went on to point out numerous example of
things that look like steps in the evolution of
the eye in a variety of different animals, very
close to our current understanding of how, in
fact, the eye evolved. He adds, If it could be
demonstrated that any complex organ existed,
which could not possibly have been formed by
numerous, successive, slight modifications, my
theory would absolutely break down. But I can
find out no such case. In recent years
intelligent design advocates have listed such
complex organs, but evolutionary biologists have
been successful in determining how they evolved,
often from organs that originally served other
purposes.
41
We should be extremely cautious in concluding
that an organ could not have been formed by
transitional gradations of some kind. Numerous
cases could be given amongst the lower animals of
the same organ performing at the same time wholly
distinct functions. Darwin cites, as an example,
the swimbladder of fish, whose purpose was to
permit flotation at different depths in the
ocean, but which clearly evolved into the lung of
the higher vertebrates, which is used for
respiration. I can, indeed, hardly doubt that
all vertebrate animals having true lungs have
descended by ordinary generation from an ancient
prototype, of which we know nothing, furnished
with a floating apparatus or swimbladder.
42
Chapter 7 Instinct This chapter deals with
another difficulty Darwin had stated at the
beginning of Chapter 6 Thirdly, can instincts
be acquired and modified through natural
selection? What shall we say to so marvellous an
instinct as that which leads the bee to make
cells, which have practically anticipated the
discoveries of profound mathematicians? Darwin
was writing about the hexagonal shape of the wax
cells made by the honeybee. He also mentions
birds that lay their eggs in other birds nests
(avoiding having to care for them) and certain
ants that act as slaves to other ants, and other
examples.

43
Darwin indicated that instinct is difficult to
define, but that it related to habitual
activities that were not learned. He was sure
that instinct was also the result of natural
selection, which then acted on behavior as well
as physical characteristics. Instinctive
behavior would have developed very slowly, over
long periods of time. Many chapters in On the
Origin of Species were greatly abridged compared
to what they would have been had Darwin written
his big species book and not been rushed into
writing On the Origin of Species. He returned to
instinct in other books, notably The Expression
of the Emotions in Man and Animals, since he
regarded emotions as instincts that evolved
through natural selection.
44
Chapter 8 Hybridisation In Chapter 8 Darwin
discussed hybridization, the crossing of two
species (i.e., one parent from each species). It
was thought at the time that if two individuals
were of the same species, their offspring would
be fertile, but if they were of different
species, their offspring would be sterile. The
hybrids are usually sterile, and when they are
fertile the offspring of two hybrids are usually
sterile. Darwin argued that this may just be
because of dissimilarities in their reproductive
organs, not because the individuals were or were
not of the same species or same variety. Often,
however, the reasons for sterility were not
known. Darwin believed their was no good way to
distinguish between species and varieties.
45
Chapter 9 Imperfection of the Geological
Record The theory of natural selection indicates
that there were intermediate forms between
existing species and their ancestral species,
which normally would be extinct. These might
occur as fossils in the geological record but few
were known in Darwins time. He argued that
their absence is not a disproof of the theory.
Gaps in the fossil record are to be expected
because the intermediate fossils may have been
destroyed or just not yet discovered. What about
forms intermediate between two existing related
species? They may never actually have existed,
according to the theory of evolution through
natural selection, only forms intermediate
between each of them and their common ancestor.
46
In many cases, intermediate forms were never very
numerous or widespread, as natural selection was
constantly operating on these forms. Darwin
accepted Lyells theory of uniformitarianism,
that geological processes had been slowly but
constantly acting on the earths surface, in many
cases probably removing some of the intermediate
forms. Indeed, millions of years of strata have
disappeared completely in many parts of the
world. It is highly important for us to gain
some notion, however imperfect, of the lapse of
years. During each of these years, over the whole
world, the land and the water has been peopled by
hosts of living forms. What an infinite number of
generations, which the mind cannot grasp, must
have succeeded each other in the long roll of
years! Now turn to our richest geological
museums, and what a paltry display we behold!
47
Modern geology was still a young science when On
the Origin of Species was published barely 75
years after James Huttons first published work.
Since its time there has been much more work
carried out and many new fossils discovered.
Many intermediate forms have been discovered,
but, clearly, not all. Many parts of the world
that were not explored in Darwins time have been
since. Most remarkably, think of all the
paleoanthropological studies that have been
carried out on the African continent and that
have begun to fill in the tree of life
beginning with the common ancestor of chimpanzees
and humans. This particular difficulty cited by
Darwin is not presently regarded as a difficulty.
48
Chapter 10 On the Geological Succession of
Organic Beings Darwin referred back to his tree
of life in chapter 4 to describe his picture of
a succession of types as new species constantly
appear on earth, evolve and flourish, and finally
decline and become extinct, perhaps leaving
living descendants, but perhaps bringing their
line to an end. Darwin believed that the
geological record of the succession of organic
beings better agreed with the slow and gradual
modification of organic beings, through descent
with modification that with the immutability of
species, which the record clearly contradicts.
49

• Chapters 11 and 12 Geographical Distribution
• and Geographical Distribution continued
• In these chapters Darwin discusses a variety of
  topics relating evolution and speciation to
  biogeography
• Similar climates in different parts of the world
  may have similar or dissimilar species there is
  no hard and fast rule.
• Large land masses separated from each other, and
  islands, and separated bodies of water, all have
  their own generally very different species.
• When species can migrate to another land or water
  area, they may evolve into different species
  migration and natural selection both affect the
  nature of the species found.

50

1. Darwin believed species originated in one place
   and then migrated to other places, rather than
   appearing (being created) differently in
   different places.
2. Some species migrate easily (birds and plants
   whose seeds can migrate) while others do not
   (such as most land animals).
3. Geological processes caused land and water levels
   to fluctuate, affording opportunities for species
   to evolve due to the appearance and disappearance
   of water barriers. Darwin discussed the effect
   of the ice ages in leading to new and different
   species and the extinction of some.

51
Chapter 12 of The Origin of Species continues the
discussion of the effect of geographical
distribution and separation by focusing on island
life. The Galápagos Islands are used as the
prime example, because Darwin had visited them on
the voyage of the HMS Beagle and written about
their species of animals, which exhibited the
effects of natural selection. I have carefully
searched the oldest voyages, but have not
finished my search as yet I have not found a
single instance, free from doubt, of a
terrestrial mammal (excluding domesticated
animals kept by the natives) inhabiting an island
situated above 300 miles from a continent or
great continental island and many islands
situated at a much less distance are equally
barren.
52
Chapter 13 Mutual Affinities of Organic Beings
Morphology Embryology Rudimentary Organs. In
Chapter 13 Darwin shows that his theory explains
many different observations about organisms
their similarities (internal, not necessarily
external, because unrelated species may have
developed similar adaptations due to similar
environments), their morphology (structure),
embrology, and their rudimentary and atrophied
structures (relics of once-useful organs). The
naturalists grouping of organisms into various
taxa (species, genera, etc.) is the result of a
relationship due to descent with modification
(evolution in modern language) from common
ancestors. Darwin insists that assuming the
existence of a divine plan adds nothing to our
understanding of natural relationships.
53
The evolutionary relationships are evident in
homologous structures What can be more curious
than that the hand of a man, formed for grasping,
that of a mole for digging, the leg of the horse,
the paddle of the porpoise, and the wing of the
bat, should all be constructed on the same
pattern, and should include the same bones, in
the same relative positions? 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.
54
Chapter 14 Recapitulation and Conclusion In
his concluding chapter, Darwin summarized the
implications of his argument, confidently adding
that young and rising naturalists would share
his vision and reject the prejudices that led
many biologists to cling to older ideas. This
chapter includes Darwins only use of the word
evolved (or any variations thereof) its the
last word of the book. Remember that Darwin
never spoke of evolution, rather of descent
with modification.
55
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.
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Chapter 14 continued Darwins last chapter refers
to the whole book as one long argument. He
summarizes his theory and its difficulties, and
states that he believes it will lead to a
revolution in natural history. The closing
paragraph of On the Origin of Species 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.
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Closing paragraph, continued 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.
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Closing paragraph, concluded 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. The last word of The Origin
of Species is the only example in the book of the
word evolved or any words with the same root.
Presumably he tried to avoid using the word
because Lamarck and Chambers had used it and been
criticized.
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Common Ancestor
Evidence for a Common Ancestor of All Life on
Earth 1869 Nucleic acids were first isolated by
Friedrich Miescher. 1944 Avery et al. identify
DNA was identified as the genetic material of all
life conceivably there could have been many
different genetic materials, or possibly each
species could have had a different genetic
material. (Maybe currently unknown species might
have genetic materials different from DNA.)
However, all known life uses the same polymer,
polynucleotide (DNA or RNA), for storing species
specific information. All known organisms base
replication on the duplication of this
molecule. 1953 Crick and Watson discover the
molecular structure of DNA a double helix. The
DNA used by living organisms is synthesized using
only four nucleosides (deoxyadenosine,
deoxythymidine, deoxycytidine, and
deoxyguanosine) out of the dozens known (at least
102 occur naturally).
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LUCA Last Universal Common Ancestor Working
backwards in time, all life apparently had at
least one common ancestor, perhaps more. Perhaps
there were several early life forms maybe some
with different genetic material, not the DNA or
RNA we are familiar with. But if so, all but one
disappeared (unless there are other life forms on
Earth, with different genetic material, that we
have not yet discovered). Of the common ancestors
of all known life on Earth, the last one before
the first is the Last Universal Common
Ancestor, or LUCA.
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In 1864 Darwin complained that Wallace always
spoke of Darwins theory without giving himself
credit, and Wallace wrote back As to the theory
of Natural Selection I shall always maintain it
to be yours and yours only. You had worked it
out in details I had never thought of, years
before I had a ray of light on the subject, and
my paper would never have convinced anybody or
been noticed as more than an ingenious
speculation, whereas your book has revolutionized
the study of natural history, and carried away
captive the best men of the present
age. William Irvine, in Apes, Angels, and
Victorians, called Wallace so retiring, so
reassuring, so generous.
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Darwins only reference to humans apart from
occasional mentions like their hand bones in
the first edition of On the Origin of Species was
this Light will be thrown on the origin of man
and his history. In later editions this became
Much light will be thrown He apparently felt
there was enough in his book already to disturb
many readers without discussing humans but this
was the subject most readers were interested
in. It was not long, however, before Huxley and
Lyell wrote books on this subject Huxleys
Evidence as to Man's Place in Nature and Lyells
Geological Evidences of the Antiquity of Man,
both appearing in 1863. Darwin eventually dealt
with the topic of humans and their history in The
Descent of Man, published in 1871.