Darwin

Darwin’s life & work

Darwin’s “big idea”

A revolution?

Charles Darwin
1809 - 1882

John Stevens Henslow Adam Sedgwick

The Zoology of the Voyage of
H.M.S. Beagle (1838-’42)

Journal of Researches (1839)

Structure and Distribution of
Coral Reefs (1842)

Geological Observations on
Volcanic Islands (1844)

Geological Observations on
South America (1846)

1837: Notebooks

1842: Pencil Sketch
(35 pp.)

1844: Essay (240 pp.)

1856 – 58: Natural
Selection (unﬁnished)

1858 ...

1862 - On the various contrivances by which British and foreign orchids are
fertilised by insects

1868 - Variation of Animals and Plants Under Domestication

1872 - Descent of Man and Selection in Relation to Sex

1872 - Expression of Emotions in Man and Animals

1875 - Insectivorous Plants

1875 – Movement and Habits of Climbing Plants (orig, 1865)

1876 - The Effects of Cross- and Self-Fertilization

1876 – Autobiography (pub. 1888)

1877 - The Different Forms of Flowers on Plants of the Same Species

1880 - Power of Movement in Plants

1881 - The Formation of Vegetable Mould through the Action of Worms

Implications

Mechanism

Pathway

Fact

Evolution
“Biological (or organic) evolution is change in the
properties of populations of organisms or groups of
such populations, over the course of generations. The
development, or ontogeny, of an individual organism is
not considered evolution: individual organisms do not
evolve. The changes in populations that are
considered evolutionary are those that are ‘heritable'
via the genetic material from one generation to the
next. Biological evolution may be slight or substantial”
Douglas J. Futuyma (1998) Evolutionary Biology

7mya! 6mya! 5mya! 4mya! 3mya! 2mya! 1mya! Now!

Kenyanthropus!
platyops! Homo erectus!

Homo ergaster!

A. garhi! Homo! “Archaic”!
rudolfensis! Homo!
sapiens!
Ardipithecus! Ardipithecus! Australopithecus!
kadabba! ramidus! afarensis!
Sahelanthropus!
tchadensis! Homo!
habilis!
Modern!
Humans!
Australopithecus!
anamensis!
Australopithecus!
Orrorin! africanus!
tugenesis!

Paranthropus!
robustus!
Neandertals!

Paranthropus!
aethiopicus!
Paranthropus!
boisei!

Evolution as Path

Degree of relatedness of
modern species
Timing of splits among lineages
Characteristics of extinct
ancestors

Darwin’s Big Idea

Descent with modiﬁcation
through natural selection

Darwin’s viewpoint
Fact
Pathway: Establishment of
genealogical relationship (“tree
thinking”) with common descent
and multiplication of species via
splitting or budding
Mechanism: Natural selection
and other mechanisms

Fact #1

Potential exponential
increase of populations
(“superfecundity”)

Source: Thomas Malthus
(1798), William Paley
(1802), observation

Fact #2

Steady-state stability of
most populations

Source: observation

Fact #3

Limitation of resources

Source: observation

Inference #1

Struggle for existence among
individuals

Author of inference:
Malthus (1798)

Linear Growth Food Production

Exponential Growth Population Growth

Malthusian
Catastrophe

Fact #4

Variation between individuals

Source: observation

Fact #5

Heritability of much of this
variation

Source: animal breeders

Inference #2

Some of this variation is advantageous in certain
environments therefore differential survival, i.e. natural
selection, will occur.

Inference held by: Darwin, Alfred Russel Wallace, and
others

Inference #3

Over many generations, provided selection
pressure is maintained, evolution will occur

Inference unique to Darwin & Wallace

Fitness
Fitness is a measure of the reproductive output
of an organism with a particular genotype with
respect to that of other genotypes in a
particular environment.
For a trait to be evolutionarily relevant, it must
affect reproduction - it is not enough to affect
survival.

Analyzing Selection
Is the population variable?
Is some of the variation among individuals
within the population heritable?
Do individuals vary in their success as surviving
or reproducing?
Are survival and reproduction non-random?
Did the population change over time?

Alternatively
If there are variations in a replicating entity, and
If these are inherited, and
If one variant is more suited to some task than the
others, and
If that task directly affects survival and therefore
reproduction of the entities,
Then selection will result in evolutionary change in
the population of entities.

Non-
Random
Random
Variation
Selection

Natural Selection is not a
Random Process

Predicting the Future
No need to be able to
predict long-term course of
evolution.
Evolution is analogous to a
poker tournament.

Darwin

“I have just been writing an
audacious little discussion, to
show that organic beings are
not perfect, only perfect
enough to struggle with their
competitors.”
Letter to J.D. Hooker, 9/11/1857

Natural Selection
Nature “cares not for mere external
appearances; she may be said to scrutinize with a
severe eye, every nerve, vessel & muscle; every
habit, instinct, shade of constitution, - the whole
machinery of the organization. There will be here
no caprice, no favoring: the good will be
preserve[d] & the bad rigidly destroyed.”
“By nature, I mean the laws ordained by God to
govern the Universe.”

Origin, 2nd ed.
“A celebrated author and divine has
written to me that ‘he has gradually
learnt to see that it is just as noble a
conception of the Deity to believe
that He created a few original forms
capable of self-development into
other and needful forms, as to believe
that He required a fresh act of
creation to supply the voids caused by
the action of His laws.’”

Letter to Asa Gray
(1860)
“There seems to me too much misery in the world. I cannot
persuade myself that a beneﬁcent and omnipotent God would
have designedly created the Ichneumonidae with the express
intention of their feeding within the living bodies of caterpillars
or that a cat should play with mice... On the other hand, I cannot
anyhow be contented to view this wonderful universe, and
especially the nature of man, and to conclude that everything is
the result of brute force. I am inclined to look at everything as
resulting from designed laws, with the details, whether good or
bad, left to the working out of what we may call chance.”

Darwin
“The old argument of design in nature, as given by
Paley, which formerly seemed to me to me so
conclusive, fails, now that the law of natural
selection has been discovered. We can no longer
argue that, for instance, the beautiful hinge of a
bivalve shell must have been made by an intelligent
being, like the hinge of a door by a man. There
seems to be no more design in the variability of
organic beings and in the action of natural
selection, than in the course which the wind
blows. Everything in nature is the result of ﬁxed
laws.”

Paley

A: X is intricate and well suited to a task T
W1: X is a product of intelligent design
W2: X is a product of random physical forces
Paley claims that the likelihood of W1 given A
exceeds that of W2, i.e. P(A|W1) >> P(A|W2)

Darwin
A: X may or may not be intricate or well-suited
to a task T.
W1: X is a product of intelligent design
W2: X is a product of a non-random natural
mechanism
Darwin claims that the likelihood of W2 given A
exceeds that of W1, i.e. P(A|W2) >> P(A|W1)

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Sexual
Selection

Inter-male competition
Female choice

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1858 was not “marked by
any of those striking
discoveries which at once
revolutionize, so to speak,
the department of science on
which they bear.”

“When the ideas advanced
by me in this volume, or
when analogous views on
the origin of species are
generally admitted, we can
dimly foresee that there will
be a considerable revolution
in natural history”

Some Questions

What was before?
What happened?
What was after?
How quickly did the change happen

Some Questions
What was before?

Transmutation of Species
‘Struggle’ with biosphere & other
organisms
Natural Selection

Classical
Precursors
Anaximader (~600 BCE):
Humans from ﬁsh

Empedocles (~450 BCE):
Combination of parts

Lucretius (~75 BCE): From
atoms to humans

Buffon

Limited
Variation

Speciation
due to
Environment

Jean Baptiste Pierre Antoine de
Monet, le chevalier de Lamarck
a believer in the great age of the
Earth
a gradualist
a strong supporter of the
importance of behavior and the
environment
a believer in branching evolution
the ﬁrst modern evolutionist

Natural Selection
1818 - William Wells: Two essays: On Upon Single Vision
with Two Eyes;The Other on Dew…and An Account of a
Female of the White Race…Part of Whose Skin Resembles
That of a Negro…By the Late W.C. Wells…with a Memoir
of His Life,Written by Himself.
1831 - Patrick Matthew: Naval Timber and Arboriculture.
1835 - Edward Blyth: “An Attempt to Classify the
‘Varieties’ of Animals, with Observations on the Marked
Seasonal and Other Changes Which Naturally Take
Place in Various British Species, and Which Do Not
Constitute Varieties“ Magazine of Natural History

Some Questions
What happened?

Accumulation of evidence, but for
what?
Consilience of inductions
(Whewell)

Instinct

Classification Fossil Record

Evolution

Embryology Morphology

Geographic
Distribution

Some Questions

What was after?

Acceptance of evolution and of
naturalistic mechanism but
rejection of natural selection

Cohen’s Stages
The “intellectual revolution” or “revolution-in-
itself” (private)
Written commitment to the new method,
concept or theory (private)
Dissemination of the ideas (public)
Adoption by a critical mass of individuals or
groups (public)

Some Questions

How quickly did the change?

Not very!

A 75 Year “Revolution”
1859
- Origin of Species
1870’s -
Rise of Neo-Lamarckianism
1899 - Herman Bumpus’ evidence for natural
selection
1900 - Re-discovery of Mendel
1901- WFR Wheldon’s evidence for natural
selection.
1930’s - “The Modern Synthesis”

Darwin’s Legacy

We have a professional,
discipline and an entirely
convincing, naturalistic
explanation of the design-like
appearance of the natural
world.

Natural
Selection

Economy of
Tree Thinking
Nature

Gradual Genealogical
Change Classification

Darwin

Biogeographic
Coevolution
Distribution

Sexual Selective
Selection Extinction

Deep Time

“Darwinists” do not exist

Evolution ≠ “Darwinism”

No Revolution?
“Evolution had become
respectable. No revolution
took place, no pyrotechnics,
just a quiet change at the top –
a palace coup. Society would
never be the same.”
James Moore

Do you think that Darwin’s
Theory of Evolution is ...

1%

29%
35%
Suported by evidence
Not supported by evidence
Don’t know enough
No Opinion

35%

Gallup 11/19/04

Theistic
Naturalistic
Non-Evolutionary

38%

47%

15%

2010

“America’s moral
decline is a product of
the Darwinian
worldview - which, in
turn, is a revival of
ancient materialist
philosophy.”

Nancy Pearcy, Discovery Institute

Darwin
“There is grandeur in this view of life, with its
several powers, having originally been 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.

Darwin

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Editor's Notes