Punctuated Equilibrium Theory Versus Gradualism Theory

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Punctuated Equilibrium Theory Versus Gradualism
Theory
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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

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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.

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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
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Basic Definition of Gradualism
http//astrobiology.ucla.edu/ESS116/L05/051620phy
letic20gradualism.jpg
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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)

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Graph of Gradual Evolution

• http//anthro.palomar.edu/synthetic/images/graph_o
  f_phyletic_gradualism.gif

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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
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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
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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
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The Basic Definition of Punctuated Equilibrium
http//astrobiology.ucla.edu/ESS116/L05/051620phy
letic20gradualism.jpg
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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.

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

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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.

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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.

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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.

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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).

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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.

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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.

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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.

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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
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