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Argentina
C. Observations
4. Biogeography
- Community Convergence
In similar environments, there are
organisms that fill similar ecological
roles – and they are
morphologically similar.
Correlated patterns…
Australia
C. Observations
4. Biogeography – Island Faunas
C. Observations
4. Biogeography – Island Fauna
- Fauklands – species same as mainland
- Galapagos – species different from mainland
a. degree of isolation correlated with uniqueness of inhabitants…..
Voyage of the Beagle – Darwin (1845) "The natural history of these islands is
eminently curious, and well deserves attention. Most of the organic
productions are aboriginal creations, found nowhere else;
Flightless Cormorant
“…there is even a difference between the inhabitants of the different islands;
yet all show a marked relationship with those of America, though separated
from that continent by an open space of ocean, between 500 and 600 miles in
width.”
Green Iguana – Central and
South America
“…The archipelago is a little world within itself, or rather a satellite attached to
America, whence it has derived a few stray colonists, and has received the
general character of its indigenous productions. Considering the small size of
the islands, we feel the more astonished at the number of their aboriginal
beings, and at their confined range.”
Galapagos Land Iguana,
pallid species, only on
Santa Fe island.
“… Seeing every height crowned with its crater, and the boundaries of most of
the lava streams still distinct, we are led to believe that within a period
geologically recent the unbroken ocean was here spread out.”
“…Hence, both in space and time, we seem to be brought somewhat near to
that great fact -- that mystery of mysteries -- the first appearance of new
beings on this earth.”
The Voyage of the Beagle – Charles Darwin
C. Observations
4. Biogeography – Island Faunas
a. Isolation correlates with uniqueness
C. Observations
4. Biogeography – Island Faunas
a. Isolation correlates with uniqueness
b. islands are dominated by dispersive forms
C. Observations
4. Biogeography – Island Faunas
a. Isolation correlates with uniqueness
b. islands are dominated by dispersive forms
c. there is even variation among islands
- Finches
"Seeing this gradation and diversity of structure in one small,
intimately related group of birds, one might really fancy that from
an original paucity of birds in this archipelago, one species had
been taken and modified for different ends."
- Mockingbirds
- Mockingbirds
Darwin classified four varieties of one species:
One species
- Mockingbirds
John Gould, the premiere ornithologist of the day, classified these as
four species:
- Mockingbirds
Darwin began to think… could the variation WITHIN species
eventually lead to variation BETWEEN species?
Could organisms in a species become so different that they become different
species?
C. Observations
4. Biogeography – Island Faunas
- How did these animals get here?
Everything points to migration from Americas
C. Observations
4. Biogeography – Island Faunas
- How did these animals get here?
Everything points to migration
- But if ancestors migrated from Americas,
C. Observations
4. Biogeography – Island Faunas
- How did these animals get here?
Everything points to migration
- But if ancestors migrated from Americas,
then the species must have changed over time
into the species we observe there today….
Because they are not the same.
C. Observations
5. Argument for Evolution as Historical Fact:
P1: Species that are alive today are different from those that have lived
previously.
P2: Spontaneous Generation is refuted, so organisms only come from other
organisms.
C1: Thus, the organisms alive today must have come from those pre-existing,
yet different, species.
C2: There must have been change through time (evolution).
Corollary: The fossil record, vestigial organs, and homologies are all
explicable and logical in this context, and inexplicable (even heritical) in some
theological contexts (imperfection).
I. Darwin’s Contributions
A. His Life
B. Origin of Species
C. Observations
D. Hypothesis – How Change Occurs
D. Hypothesis – How Change Occurs
1. Transitional Observations
a. Domesticated Animals
D. Hypothesis – How Change Occurs
1. Transitional Observations
a. Domesticated Animals
D. Hypothesis – How Change Occurs
1. Transitional Observations
a. Domesticated Animals
Humans can change the characteristics of a species by ‘selecting’
for particular traits. This can lead to the expression of extreme variation,
well beyond the original range of variation in the initial group.
Selection can create…. There are no wolves that are as small as
Chihuahuas…
D. Hypothesis – How Change Occurs
1. Transitional Observations
b. 1844: Darwin Reads Malthus - Essay On the Principle of
Population (1798)
Thomas Malthus (1766-1834)
D. Hypothesis – How Change Occurs
1. Transitional Observations
b. 1844: Darwin Reads Malthus - Essay On Population
P1: All populations have the capacity to ‘over-reproduce’
P2: Resources are finite
C: There will be a “struggle for existence”… most
offspring born will die before reaching reproductive age.
D. Hypothesis – How Change Occurs
2. Natural Selection
P1: All populations have the
capacity to ‘over-reproduce’
P2: Resources are finite
C: There will be a “struggle for
existence”
P3: Organisms in a population
vary, and some of this
variation
is heritable
D. Hypothesis – How Change Occurs
2. Natural Selection
P1: All populations have the capacity to ‘over-reproduce’
P2: Resources are finite
C: There will be a “struggle for existence”
P3: Organisms in a population vary, and some of this
variation is
heritable
C2: Some organisms, as a consequence of their inherited traits, will
be more likely to survive and reproduce than others. There will be “differential
reproductive success.”
D. Hypothesis – How Change Occurs
2. Natural Selection
C2: Some organisms, as a consequence of their inherited traits, will
be more likely to survive and reproduce than others. There will be “differential
reproductive success.”
C3: So, adaptive traits will be passed on in a population at higher
frequency than less adaptive traits. These adaptive traits will accumulate in a
population. The population will change over time. LINEAGE EVOLUTION.
D. Hypothesis – How Change Occurs
2. Natural Selection
C2: Some organisms, as a consequence of their inherited traits, will
be more likely to survive and reproduce than others. There will be “differential
reproductive success.”
C3: Over time, adaptive traits will be passed on in a population at
higher frequency than less adaptive traits. These adaptive traits will
accumulate in a population. The population will change over time. LINEAGE
EVOLUTION.
Corollary: Two populations, adapting to different environments, will
become different from one another; perhaps so different that they are unable to
mate, and are different species RADIATIONAL EVOLUTION.
E. Dilemmas
1. Evolution of complex traits
E. Dilemmas
1. Evolution of complex traits
E. Dilemmas
1. Evolution of complex traits
- "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 in the lower animals of organs performing at the same time wholly
distinct functions"
E. Dilemmas
1. Evolution of complex traits
2. Where are the continuous sequences of transitional
forms, both through time and at present (connecting
existing species?)
X
X
X
X
?
X
X
X
X
X
E. Dilemmas
1. Evolution of complex traits
2. Where are the continuous sequences of transitional
forms?
-the fossil record is incomplete – not all species leave a fossil
-Keep looking…
E. Dilemmas
1. Evolution of complex traits
2. Where are the continuous
sequences of transitional
forms?
1861:
Archeopteryx Lithographica
E. Dilemmas
1. Evolution of complex traits
2. Where are the continuous
sequences of transitional
forms?
- Connecting species:
Adapted forms swamp intermediates, which are
typically rare and are not as 'perfected' as adapted forms...
E. Dilemmas
1. Evolution of complex traits
2. Where are the continuous sequences of transitional
forms?
3. How are instincts evolved?
E. Dilemmas
1. Evolution of complex traits
2. Where are the continuous sequences of transitional
forms?
3. How are instincts evolved?
close study demonstrates that instincts also vary; so selection can act
on them if they are heritable like a morphological trait.
E. Dilemmas
1. Evolution of complex traits
2. Where are the continuous sequences of transitional
forms?
3. How are instincts evolved?
4. How do sterility barriers evolve? And how are sterile castes selected
for???
E. Dilemmas
1. Evolution of complex traits
2. Where are the continuous sequences of transitional
forms?
3. How are instincts evolved?
4. How do sterility barriers evolve? And how are sterile castes selected
for???
5. Source of heritable variation?
E. Dilemmas
1. Evolution of complex traits
2. Where are the continuous sequences of transitional
forms?
3. How are instincts evolved?
4. How do sterility barriers evolve? And how are sterile castes selected
for???
5. Source of heritable variation?
- Natural selection should “weed out” poorly adapted forms
over time, making the organisms in the population more similar (less variation).
Why is there still so much variation in natural populations?
E. Dilemmas
1. Evolution of complex traits
2. Where are the continuous sequences of transitional
forms?
3. How are instincts evolved?
4. How do sterility barriers evolve? And how are sterile castes selected
for???
5. Source of heritable variation?
- and if heredity is governed by blending traits, then how is
variation produced generation after generation?
E. Dilemmas
1. Evolution of complex traits
2. Where are the continuous sequences of transitional
forms?
3. How are instincts evolved?
4. How do sterility barriers evolve? And how are sterile castes selected
for???
5. Source of heritable variation?
- Darwin’s explanations:
- Lamarckian “use and disuse”
- and ‘gemmules’…
F. Darwinian Evolution
1. Darwin’s Model
Sources of Variation
Causes of Change
????????????????  VARIATION  NATURAL SELECTION
(use and disuse??)
F. Darwinian Evolution
2. A Summary of Darwin's Theories (from Mayr)
- Evolution as such - change over time
- Common Descent - not Lamarckian transformationalism
- Gradualism - incremental, uniformitarian change
- Populational Change in Frequencies of Traits
not changes in individuals becoming perfect
- Natural Selection - changes due to differential
reproductive success
Post Darwinian Developments
I. Physics
A. The Age of the Earth
1. 1862 - William Thompson - "Lord Kelvin"
2. 1896 - Henri Becquerel
- discovers emission of Uranium
3. 1903 - Pierre and Marie Curie
- discover emission from new element - Radium
4. 1904 - Ernst Rutherford
- "The discovery of the radio-active elements, which in their
disintegration liberate enormous amounts of energy, thus increases the
possible limit of the duration of life on this planet, and allows the time claimed
by the geologist and biologist for the process of evolution."
Post Darwinian Developments
II. Geology
A. The Dynamic Earth
Post Darwinian Developments
II. Geology
A. The Dynamic Earth
Continental Drift
- 1915 - Alfred Wegener
- Not accepted until the 1960’s and 1970’s, when sea floor spreading
was observed, sonar was used to map the ocean, and paleomagnetism
demonstrated where continents had been in the past relative to magnetic
north.
- North and South Atlantic and Indian Ocean Basins.
Post Darwinian Developments
III. Paleontology
A. Intermediate Fossils
FISH
AMPHIBIANS
Ichthyostega
- Fins and gill covers (FISH)
- Feet (AMPHIBIANS)
XXX
- After fish, before amphibians (just
where evolution predicts it should be)
D. Devonian (417-354 mya)
- Placoderms
- Sharks
- Lobe-finned Fishes
365 mya
385 mya
Archeopteryx
- Fingers, teeth, tail (Reptiles)
-Feathers (birds)
- After reptiles, before birds (just where
evolution predicts it should be)
REPTILES
BIRDS
XXX
Therapsids
REPTILES
MAMMALS
- Mammalian skeleton
- Intermediate ear
- scales
XXX
- After reptiles, before mammals (just
where evolution predicts it should be)
Mammals from the
Jurassic (185 mya)
Therapsids from the Permian (280 mya) to
the Triassic (200mya)
Pelycosaur Reptiles of the
Carboniferous (300 mya)
Australopithecines
Australopithecus afarensis
Legs
Australopithecines
- bipedal (human trait)
- chimp-sized cranial volume
APES
HUMANS
- After apes, before humans (just where
evolution predicts it should be)
XXX
Post-Darwinian Facts
I. Physics
II. Geology/Paleontology
III. Genetics
Post-Darwinian Facts
I. Physics
II. Geology/Paleontology
III. Genetics
- Genetic info is particulate (no blending)
- Variation produced by new combinations of particles
(crossing over and ind. assort.)
Post-Darwinian Facts
I. Physics
II. Geology/Paleontology
III. Genetics
IV. The Modern Synthesis – 1940’s
The Modern Synthetic Theory of Evolution
Mutation
Recombination
VARIATION
Sources of Variation
Agents of Change
N.S.
Drift
- crossing over
Migration
- independent assortment
Mutation
So, if NO AGENTS are acting on a population,
then it will be in equilibrium and WON'T change.
Non-random Mating
Beyond the Synthesis
1. Peripatric Speciation (Mayr)
Beyond the Synthesis
1. Peripatric Speciation (Mayr)
2. Punctuated Equilibrium (Eldridge and Gould – 1972)
- 1972 - Eldridge and Gould - Punctuated Equilibrium
VARIATION
1. Consider a large, well-adapted population
TIME
- 1972 - Eldridge and Gould - Punctuated Equilibrium
1. Consider a large, well-adapted population
VARIATION
Effects of Selection and Drift are small - little
change over time
TIME
- 1972 - Eldridge and Gould - Punctuated Equilibrium
VARIATION
2. There are always small sub-populations "budding off" along the
periphery of a species range...
TIME
- 1972 - Eldridge and Gould - Punctuated Equilibrium
2. Most will go extinct, but some may survive...
VARIATION
X
X
X
TIME
- 1972 - Eldridge and Gould - Punctuated Equilibrium
2. These surviving populations will initially be small, and in a new
environment...so the effects of Selection and Drift should be
strong...
VARIATION
X
X
X
TIME
- 1972 - Eldridge and Gould - Punctuated Equilibrium
3. These populations will change rapidly in response...
VARIATION
X
X
X
TIME
- 1972 - Eldridge and Gould - Punctuated Equilibrium
3. These populations will change rapidly in response... and as they
adapt (in response to selection), their populations should increase
in size (because of increasing reproductive success, by definition).
VARIATION
X
X
X
TIME
- 1972 - Eldridge and Gould - Punctuated Equilibrium
3. As population increases in size, effects of drift decline... and as a
population becomes better adapted, the effects of selection
decline... so the rate of evolutionary change declines...
VARIATION
X
X
X
TIME
- 1972 - Eldridge and Gould - Punctuated Equilibrium
4. And we have large, well-adapted populations that will remain
static as long as the environment is stable...
VARIATION
X
X
X
TIME
- 1972 - Eldridge and Gould - Punctuated Equilibrium
5. Since small, short-lived populations are less likely to leave a
fossil, the fossil record can appear 'discontinuous' or 'imperfect'
VARIATION
X
X
X
TIME
- 1972 - Eldridge and Gould - Punctuated Equilibrium
5. Large pop's may leave a fossil....
VARIATION
X
X
X
TIME
- 1972 - Eldridge and Gould - Punctuated Equilibrium
5. Small, short-lived populations probably won't...
VARIATION
X
X
X
TIME
- 1972 - Eldridge and Gould - Punctuated Equilibrium
6. So, the discontinuity in the fossil record is an expected result of
our modern understanding of how evolution and speciation occur...
VARIATION
X
X
X
TIME
- 1972 - Eldridge and Gould - Punctuated Equilibrium
6. both in time (as we see), and in SPACE (as changing
populations are probably NOT in same place as ancestral species).
VARIATION
X
X
X
TIME
Beyond the Synthesis
1. Peripatric Speciation (Mayr)
2. Punctuated Equilibrium (Eldridge and Gould – 1972)
3. Evo-devo: the importance of developmental programs
Evo-Devo – the influence of developmental programs
1. Core Processes
- Basic biological processes are
CONSERVED, and the enzymes that
perform them are CONSERVED:
- Many enzymes are more than
50% similar in AA sequence in E. coli
and H. sapiens, though separated by 2
billion years of divergence.
- Of 548 metabolic enzymes in
E. coli, 50% are present in ALL LIFE,
and only 13% are unique to bacteria.
Evo-Devo – the influence of developmental programs
1. Core Processes
- Basic biological processes are
CONSERVED, and the enzymes that
perform them are CONSERVED:
- Many enzymes are more than
50% similar in AA sequence in E. coli
and H. sapiens, though separated by 2
billion years of divergence.
- Of 548 metabolic enzymes in
E. coli, 50% are present in ALL LIFE,
and only 13% are unique to bacteria.
- So the variation and diversity of life is
NOT due to changes in metabolic or
structural genes... we are all built out of
the same stuff, that works the same
way at a cellular level.
Evo-Devo – the influence of developmental programs
- Variation is largely due to HOW
these processes are
REGULATED... 300 cell types in
humans, all descended from the
zygote; all genetically the same.
- Best (and most fundamental)
examples are HOX genes. These
are 'homeotic genes' that produce
a variety of transcription factors.
The production and localization of
these transcription factors are
CRITICAL in determining the
‘developmental compartments' of
bilaterally symmetrical animals.
Evo-Devo – the influence of developmental programs
- Effects can be profound
- 'Master Switches' that initiate downstream
cascades that can be very different... like
compound or vertebrate eyes.
Beyond the Synthesis
VARIATION
Recombination
DEVELOPMENT
Mutation
Agents of Change
PHYSIOLOGY
Sources of Variation
Selection
Drift
Mutation
Migration
Non-Random Mating