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Evolution
Species change over time,
in part because of how they
interact with their
environment (ecology).
I.
Darwin
A. Evolution and Common Ancestry
Concludes that species change over time, diverging from
one another and their common ancestors as they adapt to new
environments
Plate from The Origin of Species, 1859
1837 notebook
I.
Darwin
A. Evolution and Common Ancestry
As a consequence of:
- stratigraphic patterns in the fossil record
I.
Darwin
A. Evolution and Common Ancestry
As a consequence of:
- stratigraphic patterns in the fossil record
- evidence from morphology
Homologous Structures:
Same parts, but different uses
in different environments
(correlated pattern)
I.
Darwin
A. Evolution and Common Ancestry
As a consequence of:
- stratigraphic patterns in the fossil record
- evidence from morphology
Analogous Structures:
Different parts, but same uses
in same environment
(correlated pattern)
I.
Darwin
A. Evolution and Common Ancestry
Whale embryo
w/leg buds
As a consequence of:
- stratigraphic patterns in the fossil record
- evidence from morphology
Vestigial and embryonic
Structures:
No used in one species but
functional in others
Haeckel (after Darwin)
I.
Darwin
A. Evolution and Common Ancestry
As a consequence of:
- stratigraphic patterns in the fossil record
- evidence from morphology
- evidence from biogeography
Community Convergence:
In similar environments,
unrelated organisms play
parallel roles and converge
morphologically and ecologically
I.
Darwin
A. Evolution and Common Ancestry
As a consequence of:
- stratigraphic patterns in the fossil record
- evidence from morphology
- evidence from biogeography
Island Communities:
In isolated environments,
colonists change in response to
new conditions
I.
Darwin
A. Evolution and Common Ancestry
B. Mechanism of Change: Natural Selection
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.
I.
Darwin
A. Evolution and Common Ancestry
B. Mechanism of Change: Natural Selection
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.
P3: Organisms in a population vary, and some of this variation is heritable
I.
Darwin
A. Evolution and Common Ancestry
B. Mechanism of Change: Natural Selection
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.
P3: Organisms in a population vary, and some of this variation is heritable
C2: As a result of this variation, some organisms will be more likely to
survive and reproduce than others – there will be differential reproductive
success.
I.
Darwin
A. Evolution and Common Ancestry
B. Mechanism of Change: Natural Selection
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.
P3: Organisms in a population vary, and some of this variation is heritable
C2: As a result of this variation, some organisms will be more likely to
survive and reproduce than others – there will be differential reproductive
success.
C3: The population changes through time, as adaptive traits accumulate in
the population.
I.
Darwin
A. Evolution and Common Ancestry
B. Mechanism of Change: Natural Selection
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.
P3: Organisms in a population vary, and some of this variation is heritable
C2: As a result of this variation, some organisms will be more likely to
survive and reproduce than others – there will be differential reproductive
success.
C3: The population changes through time, as adaptive traits accumulate in
the population.
Corollary: Two populations, isolated in different environments, will diverge
from one another as they adapt to their own environments. Eventually,
these populations may become so different from one another that they are
different species.
I.
Darwin
Sources of Variation
?
V
A
R
I
A
T
I
O
N
Agents of Change
Natural Selection
I.
II.
Darwin
Genetics
Sources of Variation
Mutation
Recombination
- crossing over
- independent assortment
Agents of Change
V
A
R
I
A
T
I
O
N
Natural Selection
Mutation
Units of heredity (genes) don’t blend together; they are ‘particulate’ and are passed
in new combinations to offspring.
In a diploid species, each parent makes 2n combinations of chromosomes in their
gametes, without accounting for crossing-over!
I. Darwin
II. Genetics
III. Population Genetics and The Modern Synthesis
A. Model
Sources of Variation
Mutation
Recombination
- crossing over
- independent assortment
V
A
R
I
A
T
I
O
N
Agents of Change
Natural Selection
Mutation
Drift
Migration
Non-Random Mating
Rates of mutation are low; mutation is important as a source of new genes, but
doesn’t change frequencies much. Selection and drift are major agents of
change.
I. Darwin
II. Genetics
III. Population Genetics and The Modern Synthesis
A. Model
B. Drift
- two patterns related to population size
I. Darwin
II. Genetics
III. Population Genetics and The Modern Synthesis
A. Model
B. Drift
- two patterns related to population size
- “Genetic Bottleneck”
If a population crashes (perhaps as the result of a plague) there will be both selection and
drift. There will be selection for those resistant to the disease (and correlated selection
for genes close to the genes conferring resistance), but there will also be drift at other loci
simply by reducing the size of the breeding population.
European Bison, hunted to
12 individuals, now number
over 1000.
Cheetah have very low
genetic diversity,
suggesting a severe
bottleneck in the past.
They can even
exchange skin grafts
without rejection…
Fell to 100’s in the 1800s,
now in the 100,000’s
- “Founder Effect” and Huntington’s Chorea
HC is a neurodegenerative disorder caused by
an autosomal lethal dominant allele.
The fishing villages around Lake Maracaibo in
Venezuela have the highest incidence of
Huntington’s Chorea in the world, approaching
50% in some communities.
By comparing pedigrees, she traced the
incidence to a single woman who arrived 200
years ago. When the population was small, she
had 10 children who survived and reproduced.
Folks with HC now trace their ancestry to this
lineage.
I.
II.
III.
IV.
Darwin
Genetics
Population Genetics and The Modern Synthesis
Modern Evolutionary Theory
A. Peripatric Speciation
I.
II.
III.
IV.
Darwin
Genetics
Population Genetics and The Modern Synthesis
Modern Evolutionary Theory
A. Peripatric Speciation
B. Punctuated Equilibrium
Niles Eldridge
Stephen J. Gould
B. Punctuated Equilibrium – Eldridge and Gould
VARIATION
1. Consider a large, well-adapted population
TIME
B. Punctuated Equilibrium – Eldridge and Gould
1. Consider a large, well-adapted population
VARIATION
Effects of Selection and Drift are small - little change
over time
TIME
B. Punctuated Equilibrium – Eldridge and Gould
VARIATION
2. There are always small sub-populations "budding off" along the
periphery of a species range...
TIME
B. Punctuated Equilibrium – Eldridge and Gould
2. Most will go extinct, but some may survive...
X
VARIATION
X
X
TIME
B. Punctuated Equilibrium – Eldridge and Gould
2. These surviving populations will initially be small, and in a new
environment...so the effects of Selection and Drift should be strong...
X
VARIATION
X
X
TIME
B. Punctuated Equilibrium – Eldridge and Gould
3. These populations will change rapidly in response...
X
VARIATION
X
X
TIME
B. Punctuated Equilibrium – Eldridge and Gould
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).
X
VARIATION
X
X
TIME
B. Punctuated Equilibrium – Eldridge and Gould
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...
X
VARIATION
X
X
TIME
B. Punctuated Equilibrium – Eldridge and Gould
4. And we have large, well-adapted populations that will remain static as
long as the environment is stable...
X
VARIATION
X
X
TIME
B. Punctuated Equilibrium – Eldridge and Gould
5. Since small, short-lived populations are less likely to leave a fossil, the
fossil record can appear 'discontinuous' or 'imperfect'
X
VARIATION
X
X
TIME
B. Punctuated Equilibrium – Eldridge and Gould
5. Large pop's may leave a fossil....
X
VARIATION
X
X
TIME
B. Punctuated Equilibrium – Eldridge and Gould
5. Small, short-lived populations probably won't...
X
VARIATION
X
X
TIME
B. Punctuated Equilibrium – Eldridge and Gould
6. So, the discontinuity in the fossil record is an expected result of our
modern understanding of how evolution and speciation occur...
X
VARIATION
X
X
TIME
B. Punctuated Equilibrium – Eldridge and Gould
6. both in time (as we see), and in SPACE (as changing populations are
probably NOT in same place as ancestral species).
X
VARIATION
X
X
TIME
I.
II.
III.
IV.
Darwin
Genetics
Population Genetics and The Modern Synthesis
Modern Evolutionary Theory
A. Peripatric Speciation
B. Punctuated Equilibrium
C. Genes and Development: “Evo-Devo”
…explain changes like this?
Can changes like this….
C. Genes and Development: "Evo-Devo"
…explain changes like this?
Can changes like this….
Differences correlate with what they
make (different proteins make them
different colors)
Differences don’t correlate with what
they make; they are pretty much the
same stuff, just in a different shape.
C. Genes and Development: "Evo-Devo"
C. Evo-Devo – the influence of regulatory genes
.
Antennules detect chemicals secreted
by predatory fish
Stimulate release of dopamine in the
brain
Brain releases juvenile hormone
(growth hormone in inverts)
Growth of particular body parts
continues, creating a sharp “helmet”
and longer “spine” that reduce
predation.
Selection for an inducible
developmental pathway
Without Fish
With Fish
IV. Modern Evolutionary Theory
A. Peripatric Speciation
B. Punctuated Equilibrium
C. Genes and Development: “Evo-Devo”
D. Model
Sources of Variation
Mutation
Recombination
- crossing over
- independent assortment
D
E
V
E
L
O
P
M
E
N
T
V
A
R
I
A
T
I
O
N
Agents of Change
Natural Selection
Drift
Mutation
Migration
Non-random Mating