Title: Punctuated Equilibrium Theory Versus Gradualism Theory
1Punctuated Equilibrium Theory Versus Gradualism
Theory
2Overview of Topic
- Important Definitions
- A thorough look at Gradualism
- Examples of Gradualism
- A thorough look at Punctuated Equilibrium
- Examples of Punctuated Equilibrium
- The Fossil Record
- Rate of Early Evolution
- Which theory is being used today
- Questions
- References
3Other Definitions That are Key to this
presentation
- Anagenesis Is evolution within a lineage. This
is the same as gradualism because in gradualism
evolution follows a slow pattern. Sometimes
confusion can occur when people switch the terms
interchangeable. Since Punctuated Equilibrium
does not follow any known pattern, it is not
considered an Anagenic form of evolution. - Cladogenesis is evolution that results in the
splitting of a lineage. Because punctuated
equilibrium is a theory that claims evolution
does not always follow a linear pattern it
follows the cladogenesis pattern of evolution. - Neontology The study of presently alive or
recently extinct organisms. - Paleontology The study of fossils (in basic
terms). - Peripatric Speciation Geographic isolation
occurs first, resulting in no gene flow. This
Isolation is normally the result of vicariance,
dispersal and distance. - Speciation Gould suggests that rather than
becoming more diverse with time, some species
become extinct and surviving species diversify to
fill in the gaps.
4Anagenesis VS Cladogenesis
http//rainbow.ldgo.columbia.edu/courses/v1001/ana
clad.html
http//www.micro.utexas.edu/courses/levin/bio304/e
volution/phyletic.gif
5Basic Definition of Gradualism
http//astrobiology.ucla.edu/ESS116/L05/051620phy
letic20gradualism.jpg
6Further points of Gradualism
- Gradualism is a biological concept that refers to
the type of change that characterizes biological
evolution. - Evolution occurs through the accumulation of
slight modifications over a period of
generations. - Every individual is the same species as its
parents. - It is the population, not the individual, that
evolves. - (Wikipedia, the free encyclopedia)
7Graph of Gradual Evolution
- http//anthro.palomar.edu/synthetic/images/graph_o
f_phyletic_gradualism.gif
8Charles Darwin Role in the Theory of Gradualism
- Charles Darwin is the Creator of Gradualism
- Known as the father of evolution Charles Darwin
invented the theory of gradualism. He claimed
that through natural selection the individuals
with the best genetic traits would be the ones to
mate and pass on their genes. This process is
very slow since it requires countless generations
for these small changes to be realized. This made
Darwin believe that evolution happens with small
changes over very long periods.
www.counterbalance.net/ media/darwin-body.html
9 The Human example of Gradualism
- The best known example of gradualism may be the
evolution of humans. Instead of fast advancements
and spontaneous spurts of rapid evolution humans
followed a linear pattern of evolution. Although
the fossil record is still incomplete the slow
gradual changes that make homo sapiens unique
have been documented. On the chart below, the
Anagenic pattern of evolution is apparent.
http//www.leakeyfoundation.org/content/image-1571
.jpg
10Humans Evolving Diagram Two
- This picture includes both the skulls and the
outline of the actual body. It is important to
note that between stages only limited body
physiology is changed. Since human evolution is
believed to be through gradualism this diagram
you will not notice and drastic changes or
branches of other species. (sorry the diagram is
a little blurry if you wish to see a clearer one
look on the side board there is a similar poster)
http//www.brain-dynamics.net/research/brain_files
/evolution.jpg
11The Basic Definition of Punctuated Equilibrium
http//astrobiology.ucla.edu/ESS116/L05/051620phy
letic20gradualism.jpg
12Advanced Rules of Punctuated Equilibrium
- The 9 Rules of this theory
- Paleontology should be informed by neontology.
- Most speciation is cladogenesis rather than
anagenesis. - Most speciation occurs through peripatric
speciation. - Large, widespread species dont change or change
slowly - Daughter species develop in a geographically
limited region. - Daughter species develop in a stratigraphically
limited extent - Sampling of the fossil record will reveal a
pattern of most species in stasis, with abrupt
appearance of new species - Adaptive change in lineages occurs mostly during
periods of speciation. - Trends in adaptation occur through the mechanism
of species selection.
13Graph Depicts Punctuated Equilibrium
http//anthro.palomar.edu/synthetic/images/graph_o
f_punctuated_equilibrium_2.gif
14The Inventory of the Punctuated Equilibrium
Theory
- Niles Eldredge of the American Museum of Natural
History and Stephen Jay Gould of Harvard
University rejected the excuse for the missing
links in the fossil record and invented their own
theory. The Punctuated Equilibrium Theory. This
occurred in 1972 almost a half century after the
original theory was introduced.
15The T Rexellent Example of Punctuated
Equilibrium
- By viewing the fossil record it is clear that in
many cases punctuated equilibrium - occurred. These examples are as plentiful as they
are diverse. In fact it has been - proven that from small shell fish to large
dinosaurs punctuated equilibrium was - the process of evolution. The following examples
of Punctuated Equilibrium - proven by the fossil record were discovered in a
Montana by Horner, J.R., D.J. - Varrichio, and M.B. Goodwin.
- The search for fossils began in 1992 and these
examples were discovered - 50 specimens of lambeosaurids, transitional
between Lambeosaurus and Hypacrosaurus. - Transitional pachycephalosaurid between
Stegoceras and Pachycephalosaurus. - Transitional tyrannosaurid between Tyrannosaurus
and Daspletosaurus -
- The fossils showed 5 million years of
evolutionary stasis, followed by rapid
evolutionary change. The rapidly changing
environment lead to such change. The sea level
rose, drowning the Judith River Formation for
500,000 years. The dinosaurs were forced to move
to smaller areas. Being under pressure, all of
these species evolved fairly rapidly.
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17The Debate over the Gaps in the Fossil Record
- Both theories claim that they can explain the
gaps in the fossil record. The Gradualism theory
states that the fossil record is incomplete and
that it is unlikely that all stages of evolution
would be preserved let alone found. However there
have been a few species that show Gradualism
through the fossil record. Humans for example.
Punctuated Equilibrium claims the gaps in the
fossil record are not just missing links but the
actual process of evolution. They claim that he
evolution happens to rapidly to be found in a
fossil record. As shown before this has been
proven countless times from T rexes to shell
fish. - So in the after math what theory holds true?
- In the present it is still difficult to
decide which statement is true concerning the
gaps in the fossil record since a limited number
of fossils have been collected and recorded.
Research is ongoing today and possible in the
next few hundred years we may have an answer. But
remember these are both just theories and one or
both could be proven wrong.
18The Past Rates of Evolution
- Evolution in the first three billion years of
life on earth was a shining example of
Gradualism. Life on earth was made up only of
unicellular organisms who evolved extremely
slowly in a linear fashion. These organisms where
mostly Eubacteria and later after a long period
of slow change aerobic and photosynthetic
linkages Archaebacteria evolved. - However around 640 million years ago something
changed the rate of evolution. Over a 40 million
year span a mass diversification of life
occurred. This time period is known as the
Cambrian Explosion. Interestingly enough animals
representing present day major phyla and those
that are now extinct appeared during this period.
There are fossil record showing appearances of
early arthropods, primitive chordates and the
precursors to vertebrates.
19What Theory is Being Used Today?
- Punctuated Equilibrium is the more modern theory
of evolutionary rate but it has yet to be fully
proven. Gradualism is the first theory on
evolutionary rate and even though it is over a
century old it still has not been fully proven.
This has lead many scientists to make a theory
that involves both principles. They claim
evolution goes very slowly (like in Gradualism)
but with some exceptions with accelerated speed
and fast changes (like in Punctuated
Equilibrium).
20Summary
- Gradualism Created by Charles Darwin the theory
of Gradualism holds that large evolutionary
changes in species are the result of many small
and ongoing changes and processes - Punctuated Equilibrium Created by Niles and
Gould (1972). Large evolutionary change is
attributed to relatively rapid spurts of change
followed by long period of little or no change. - Past Evolutionary Rates First 3 billion years
very gradual until the Cambrian explosion when
the evolutionary rates soared. - Fossil Record Cannot definitely prove or dismiss
either theory since it is incomplete. - Current Theory A combination of both theories
including gradual and spontaneous change.
21Three Questions On Evolution
- 1. Who invented the Theory of Gradualism and the
Theory of Punctuated Equilibrium. What inspired
these people to develop these theories? - 2. How does each theory explain the gaps in the
fossil record? Can either theory prove the gaps?
Why or Why not? - 3. Give one example of an animal that went
through the process of gradualism and one that
went through the process of punctuated
equilibrium. Explain how these species went
through the process.
22Answers to Questions
- 1. Charles Darwin invented the theory of
Gradualism. He was inspired by his theory of
natural selection. He claimed that through
natural selection the individuals with the best
genetic traits would be the ones to mate and pass
on their genes. This process is very slow since
it requires countless generations for these small
changes to be realized. Niles and Gould invented
the theory of punctuated equilibrium. They were
inspired by the gaps in the fossil record. Their
theory explains the gaps in the fossil record and
how they arent actual gaps but the rate of
evolution. - 2. Gradualism holds that the gaps in the fossil
record are because not all animals are
preserved, and many fossil still must be found,
the fossil record is incomplete. Punctuated
Equilibrium holds the gaps in the fossil record
is due to the rapid evolution of a species
followed by stasis. This theory claims that the
fossil record proves their patter. In actual fact
neither theory is completely proven by the fossil
record because more paleontology must be done. - 3. Humans followed the pattern of Gradual
evolution. This is shown by the existing fossil
record that shows slow and steady evolution over
a long period of time. The T- Rex went through
the Punctuated Equilibrium pattern of evolution.
This was seen in a lake in Montana. A small
population of T-rexes were separated due to
rising water levels. Being separated from a large
gene pools lead to rapid evolution.
23Works Cited List
Suggested Reading (Charles Darwin info and
gradualism info)
http//anthro.palomar.edu/synthetic/images/graph_o
f_punctuated_equilibrium_2.gif
http//astrobiology.ucla.edu/ESS116/L05/051620phy
letic20gradualism.jpg
http//www.brain-dynamics.net/research/brain_files
/evolution.jpg
http//www.leakeyfoundation.org/content/image-1571
.jpg
http//www.as.ua.edu/ant/bindon/ant570/topics/evol
ution/img065.jpg
http//www.micro.utexas.edu/courses/levin/bio304/e
volution/phyletic.gif
http//rainbow.ldgo.columbia.edu/courses/v1001/ana
clad.html
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