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Punctuated Equilibrium Theory Versus Gradualism Theory

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Title: Punctuated Equilibrium Theory Versus Gradualism Theory


1
Punctuated Equilibrium Theory Versus Gradualism
Theory
2
Overview 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

3
Other 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.

4
Anagenesis VS Cladogenesis
http//rainbow.ldgo.columbia.edu/courses/v1001/ana
clad.html
http//www.micro.utexas.edu/courses/levin/bio304/e
volution/phyletic.gif
5
Basic Definition of Gradualism
http//astrobiology.ucla.edu/ESS116/L05/051620phy
letic20gradualism.jpg
6
Further 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)

7
Graph of Gradual Evolution
  • http//anthro.palomar.edu/synthetic/images/graph_o
    f_phyletic_gradualism.gif

8
Charles 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
10
Humans 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
11
The Basic Definition of Punctuated Equilibrium
http//astrobiology.ucla.edu/ESS116/L05/051620phy
letic20gradualism.jpg
12
Advanced 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.

13
Graph Depicts Punctuated Equilibrium
http//anthro.palomar.edu/synthetic/images/graph_o
f_punctuated_equilibrium_2.gif
14
The 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.

15
The 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.

16
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17
The 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.

18
The 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.

19
What 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).

20
Summary
  • 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.

21
Three 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.

22
Answers 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.

23
Works 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
24
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