punctuated equilibrium - OpotikiCollegeBiology

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PUNCTUATED
EQUILIBRIUM
http://www.saburchill.com/IBbiology/chapters05/017.html
NEO-DARWINISM
Evolutionary change is both slow and
gradual
 Resulting from the accumulation of many
small genetic changes favoured by natural
selection
 Other effects occasionally making small
contributions
 Gradualism
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© 2008 Paul Billiet ODWS
Evolution of new species
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Two possible ways from gradualism
PHYLETIC TRANSFORMATION
ALLOPATRIC SPECIATION
© 2008 Paul Billiet ODWS
PHYLETIC TRANSFORMATION
Gradual accumulation of small genetic
variations preserved by natural selection
 A whole population imperceptibly to
evolve in to a new species
 Impossible to draw a clear line between
the end of the first species and the
beginning of its descendant species
 There would be a long period of
intermediate forms

© 2008 Paul Billiet ODWS
ALLOPATRIC SPECIATION
Geographical or reproductive isolation of
a part of the population would allow it to
evolve in a different direction
 Possibly more rapidly than the main
population
 If the isolated population is small, it might
be very difficult to find fossils of the
intermediate stages

© 2008 Paul Billiet ODWS
Allopatric speciation
of Species W into
species X due to the
isolation of a small
population of Species
W
Species X
Species Z
Species Y
Species Y
Time
Allopatric speciation
of species Y into
species Z due to the
isolation of a small
population of species
Y
Phyletic transition of species W
into Species Y due to the slow
gradual accumulation of mutations
in Species W
Species W
© 2008 Paul Billiet ODWS
Evolution
THE PUNCTUATED
EQUILIBRIUM MODEL
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They observed that the
fossil record gives a
different picture for the
evolution
They claim that there were
long periods of stasis (410 million years) involving
little evolutionary change
Then occasional rapid
formation of new
species
As little as 5,000 - 50,000
years
© 2008 Paul Billiet ODWS
Stephen J
Gould
Niles Eldredge
Stasis and change
A species resists evolutionary change
 A species would rather move to a new
area where it can find its habitat than
adapt to a new one
 If a small population of a species should
get isolated in an area where its habitat
does not exist…
 …rapid change could take place to bring
the population back to equilibrium (stasis)
 But it is no longer the same species

© 2008 Paul Billiet ODWS
Species Y
Species Z
Species X
Stasis
Species W
Stasis
Time
Stasis
© 2008 Paul Billiet ODWS
Rapid
speciation
Rapid
speciation
Evolution
Rapid
speciation
Mechanisms
1.
2.
3.
4.
Rapid natural selection in isolated
populations
Genetic drift in small isolated
populations.
Hopeful monsters
Breakdown of developmental
homeostasis
© 2008 Paul Billiet ODWS
Criticisms
What is a species?
 How rapid is rapid?
 The incomplete fossil record

© 2008 Paul Billiet ODWS