IV. Modern Evolutionary Theory

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IV. Modern Evolutionary Theory A. Post-Darwinian
Facts B. Population Genetics C. Post-Darwinian
Theory
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IV. Modern Evolutionary Theory A. Post-Darwinian
Facts B. Population Genetics C. Post-Darwinian
Theory 1. Mutationist School (1900-1930) Richar
d Goldschmidt T. H. Morgan
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IV. Modern Evolutionary Theory A. Post-Darwinian
Facts B. Population Genetics C. Post-Darwinian
Theory 1. Mutationist School (1900-1930) 2.
The Modern Synthesis (1940)
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Post Darwinian Developments I. Genetics C.
Population Genetics 1. 1908-10 Hardy -
Weinberg - (Castle)

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Post Darwinian Developments I. Genetics C.
Population Genetics 1. 1908-10 Hardy -
Weinberg - (Castle) after one generation of
random mating, and equilibrium is reached in
genotypic frequencies.

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Post Darwinian Developments I. Genetics C.
Population Genetics 1. 1908-10 Hardy -
Weinberg - (Castle) 2. 1912-1988 Sewall
Wright

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Post Darwinian Developments I. Genetics C.
Population Genetics 1. 1908-10 Hardy -
Weinberg - (Castle) 2. 1912-1988 Sewall
Wright - plant and animal breeding -
statistical modelling of evolution - Drift -
'Wright' Effect

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Post Darwinian Developments I. Genetics C.
Population Genetics 1. 1908-10 Hardy -
Weinberg - (Castle) 2. 1912-1988 Sewall
Wright 3. 1930 - R. A. Fisher -
statistician - ANOVA - The Genetical Theory
of Natural Selection

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Post Darwinian Developments I. Genetics C.
Population Genetics 1. 1908-10 Hardy -
Weinberg - (Castle) 2. 1912-1988 Sewall
Wright 3. 1930 - R. A. Fisher 4. 1932
- J. B. S. Haldane - The Causes of
Evolution - Stressed the importance of
selection over mutation

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Post Darwinian Developments I. Genetics C.
Population Genetics 1. 1908-10 Hardy -
Weinberg - (Castle) 2. 1912-1988 Sewall
Wright 3. 1930 - R. A. Fisher 4. 1932
- J. B. S. Haldane 5. 1937 - T.
Dobzhansky - pop gen of D. psuedoobscura
inversions - Genetics and the Origin of
Species - 'isolating mechanisms'

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Post Darwinian Developments I. Genetics C.
Population Genetics 1. 1908-10 Hardy -
Weinberg - (Castle) 2. 1912-1988 Sewall
Wright 3. 1930 - R. A. Fisher 4. 1932
- J. B. S. Haldane 5. 1937 - T.
Dobzhansky 6. 1942 - Ernst Mayr -
naturalist, not geneticist - influenced
Dobzhansky's interpretations - Systematics and
the Origin of Species - biological species
concept
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Post Darwinian Developments I. Genetics C.
Population Genetics 1. 1908-10 Hardy -
Weinberg - (Castle) 2. 1912-1988 Sewall
Wright 3. 1930 - R. A. Fisher 4. 1932
- J. B. S. Haldane 5. 1937 - T.
Dobzhansky 6. 1942 - Ernst Mayr 7.
1942 - 1950 Huxley, Stebbins, Simpson
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Post Darwinian Developments I. Genetics C.
Population Genetics D. 1940's The Modern
Synthetic Theory of Evolution Sources of
Variation Agents of Change Mutation N.S.
Recombination Drift - crossing
over Migration - independent
assortment Mutation Non-random Mating
VARIATION
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IV. Modern Evolutionary Theory A. Post-Darwinian
Facts B. Population Genetics C. Post-Darwinian
Theory 1. Mutationist School (1900-1930) 2.
The Modern Synthesis (1940) 3. Impact of the
Modern Synthesis - Species and Speciation
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3. Impact of the Modern Synthesis - Species and
Speciation a. Mayr - Biological species
concept - defined species as "groups of
potentially reproducing organisms separated from
other such groups". Based on the Modern
Synthesis, Mayr suggested that speciation would
be most frequent when the two primary agents of
change were at work - DRIFT and
SELECTION ...when small populations were isolated
in new habitats... this was likely to occur when
organisms along the edge of a species range
colonized a new area... Mayr called this
Peripatric Speciation
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3. Impact of the Modern Synthesis - Species and
Speciation b. Dobzhansky - isolating
mechanisms What prevents successful reproduction?
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3. Impact of the Modern Synthesis - Species and
Speciation b. Dobzhansky - isolating
mechanisms What prevents successful
reproduction? - GEOGRAPHIC isolation
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3. Impact of the Modern Synthesis - Species and
Speciation b. Dobzhansky - isolating
mechanisms What prevents successful
reproduction? - GEOGRAPHIC isolation -
TEMPORAL isolation
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3. Impact of the Modern Synthesis - Species and
Speciation b. Dobzhansky - isolating
mechanisms What prevents successful
reproduction? - GEOGRAPHIC isolation -
TEMPORAL isolation - BEHAVIORAL isolation
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3. Impact of the Modern Synthesis - Species and
Speciation b. Dobzhansky - isolating
mechanisms What prevents successful
reproduction? - GEOGRAPHIC isolation -
TEMPORAL isolation - BEHAVIORAL isolation -
MECHANICAL isolation
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3. Impact of the Modern Synthesis - Species and
Speciation b. Dobzhansky - isolating
mechanisms What prevents successful
reproduction? - GEOGRAPHIC isolation -
TEMPORAL isolation - BEHAVIORAL isolation -
MECHANICAL isolation - PHYSIOLOGICAL isolation
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3. Impact of the Modern Synthesis - Species and
Speciation b. Dobzhansky - isolating
mechanisms What prevents successful
reproduction? - GEOGRAPHIC isolation -
TEMPORAL isolation - BEHAVIORAL isolation -
MECHANICAL isolation - PHYSIOLOGICAL
isolation - GENETIC isolation/incompatibility
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3. Impact of the Modern Synthesis - Species and
Speciation b. Dobzhansky - isolating
mechanisms What prevents successful
reproduction? - GEOGRAPHIC isolation -
TEMPORAL isolation - BEHAVIORAL isolation -
MECHANICAL isolation - PHYSIOLOGICAL
isolation - GENETIC isolation/incompatibility
- HYBRID STERILITY
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3. Impact of the Modern Synthesis - Species and
Speciation b. Dobzhansky - isolating
mechanisms What prevents successful
reproduction? - GEOGRAPHIC isolation -
TEMPORAL isolation - BEHAVIORAL isolation -
MECHANICAL isolation - PHYSIOLOGICAL
isolation - GENETIC isolation/incompatibility
- HYBRID STERILITY - DECREASED HYBRID VIGOR
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3. Impact of the Modern Synthesis - Species and
Speciation b. Dobzhansky - isolating
mechanisms
Small genetic change may be enough to cause
speciation. Speciation may be a fairly
continuous process of accumulating differences...
so defining species boundaries may be difficult
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3. Impact of the Modern Synthesis - Species and
Speciation c. Ring Species
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3. Impact of the Modern Synthesis - Species and
Speciation c. Ring Species
They show continuous variation as they moved
south on both sides of the valley. However, when
the ends of the the contiuum meet, they can't
mate. This provides a direct and dramatic
example of continuous variation creating
discontinuous variation.
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3. Impact of the Modern Synthesis - Species and
Speciation c. Speciation Rate Some
characteristics should increase the chances that
a species radiates....
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3. Impact of the Modern Synthesis - Species and
Speciation c. Speciation Rate Some
characteristics should increase the chances that
a species radiates.... - high dispersal
capacity (increase geographic isolation)
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3. Impact of the Modern Synthesis - Species and
Speciation c. Speciation Rate Some
characteristics should increase the chances that
a species radiates.... - high dispersal
capacity (increase geographic isolation) -
small (more likely to become isolated)
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3. Impact of the Modern Synthesis - Species and
Speciation c. Speciation Rate Some
characteristics should increase the chances that
a species radiates.... - high dispersal
capacity (increase geographic isolation) -
small (more likely to become isolated) -
produce lots of offspring (more successful
colonists)
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3. Impact of the Modern Synthesis - Species and
Speciation c. Speciation Rate Some
characteristics should increase the chances that
a species radiates.... - high dispersal
capacity (increase geographic isolation) -
small (more likely to become isolated) -
produce lots of offspring (more successful
colonists)
INSECTS in general, and Beetles in particular....
they fly (disperse), but poorly (don't
return...isolation). And they are tough as nails,
so they can survive to wherever they disperse.
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IV. Modern Evolutionary Theory A. Post-Darwinian
Facts B. Population Genetics C. Post-Darwinian
Theory 1. Mutationist School (1900-1930) 2.
The Modern Synthesis (1940) 3. Impact of the
Modern Synthesis - Species and Speciation 4.
Punctuated Equilibrium (1972 - Eldridge and
Gould)
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- 1972 - Eldridge and Gould - Punctuated
Equilibrium
1. Consider a large, well-adapted population
VARIATION
TIME
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- 1972 - Eldridge and Gould - Punctuated
Equilibrium
1. Consider a large, well-adapted
population Effects of Selection and Drift are
small - (it's already "well adapted" and it is
large....) little change over time
VARIATION
TIME
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- 1972 - Eldridge and Gould - Punctuated
Equilibrium
2. There are always small sub-populations
"budding off" along the periphery of a species
range...(Peripatric speciation...)
VARIATION
TIME
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- 1972 - Eldridge and Gould - Punctuated
Equilibrium
2. Most will go extinct, but some may survive...
VARIATION
X
X
X
TIME
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- 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
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- 1972 - Eldridge and Gould - Punctuated
Equilibrium
3. These populations will change rapidly in
response...
VARIATION
X
X
X
TIME
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- 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
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- 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
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- 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
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- 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
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- 1972 - Eldridge and Gould - Punctuated
Equilibrium
5. Large pop's may leave a fossil....
VARIATION
X
X
X
TIME
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- 1972 - Eldridge and Gould - Punctuated
Equilibrium
5. Small, short-lived populations probably
won't...
VARIATION
X
X
X
TIME
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- 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
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- 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
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IV. Modern Evolutionary Theory A. Post-Darwinian
Facts B. Population Genetics C. Post-Darwinian
Theory 1. Mutationist School (1900-1930) 2.
The Modern Synthesis (1940) 3. Impact of the
Modern Synthesis - Species and Speciation 4.
Punctuated Equilibrium (1972 - Eldridge and
Gould) So, our modern evolutionary theory
PREDICTS that transitional fossils should be
rare, because most evolutionary change is
occurring in small, isolated population in new
environments. This solves Darwin's remaining
dilemma regarding the 'incompleteness' of the
fossil record, and explains why we don't have
intermediates for every possible lineage. (Like
the "rats" to "bats" intermediate mentioned in
last weeks reading...no we don't have those...
but we DO have intermediates of fish to
amphibians, reptiles to birds, and apes to
humans... we shouldn't expect EVERYTHING.)