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 • Questions • References

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.

Anagenesis VS Cladogenesis

http://www.micro.utexas.edu/courses/levin/bio304/evolution/phyletic.gif http://rainbow.ldgo.columbia.edu/courses/v1001/anaclad.html

Basic Definition of Gradualism

http://astrobiology.ucla.edu/ESS116/L05/0516%20phyletic%20gradualism.jpg

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

• http://anthro.palomar.edu/synthetic/images/graph_of_phyletic_gradualism.gif

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

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

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

The Basic Definition of Punctuated Equilibrium

http://astrobiology.ucla.edu/ESS116/L05/0516%20phyletic%20gradualism.jpg

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 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

http://anthro.palomar.edu/synthetic/images/graph_of_punctuated_equilibrium_2.gif

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.

http://www.harunyahya.org/evrim/evrim_acmazi_2/res/EVRIM-ACMAZI-2-061a.jpg

The T – Rexellent Example of Punctuated Equilibrium

By viewing the fossil record it is clear that in many cases punctuated equilibriumoccurred. 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.

http://astrobiology.ucla.edu/ESS116/L05/0514%20punctuated%20equilibrium.jpg

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).

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.

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

http://astrobiology.ucla.edu/ESS116/L05/0514%20punctuated%20equilibrium.jpg

http://anthro.palomar.edu/synthetic/images/graph_of_punctuated_equilibrium_2.gif

http://astrobiology.ucla.edu/ESS116/L05/0516%20phyletic%20gradualism.jpg

http://www.brain-dynamics.net/research/brain_files/evolution.jpg

http://www.leakeyfoundation.org/content/image-1571.jpg

http://www.micro.utexas.edu/courses/levin/bio304/evolution/phyletic.gif

http://rainbow.ldgo.columbia.edu/courses/v1001/anaclad.html

http://www.as.ua.edu/ant/bindon/ant570/topics/evolution/img065.jpg

Author: Peter J. BowlerTitle: Charles Darwin The man and his influencePress: Cambridge UniversityCopy Right: 1990

Suggested Reading (Charles Darwin info and gradualism info)