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Punctuated Equilibrium Theory
Versus Gradualism Theory
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
Other Definitions That are Key to this
• 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
• Speciation Gould suggests that rather than becoming more diverse with
time, some species become extinct and surviving species diversify to fill in
the gaps.
Anagenesis VS Cladogenesis
Basic Definition of Gradualism
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)
Graph of Gradual Evolution
Charles Darwin Role in the Theory
of Gradualism
• Charles Darwin is the Creator of
• 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. media/darwinbody.html
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.
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)
The Basic Definition of Punctuated
Advanced Rules of Punctuated
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 don’t 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.
Graph Depicts Punctuated Equilibrium
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.
The T – Rexellent Example of Punctuated
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
• Transitional pachycephalosaurid between Stegoceras and
• 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.
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.
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.
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).
• 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
• Current Theory: A combination of both theories including gradual and
spontaneous change.
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.
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 aren’t 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.
Works Cited List
Suggested Reading (Charles Darwin info and gradualism info)
Author: Peter J. Bowler
Title: Charles Darwin The man and his influence
Press: Cambridge University
Copy Right: 1990