Theories of Evolution

Paper Summary:

This paper discusses the two major theories for evolution of organisms and speciation: phyletic gradualism and punctuated equilibrium. It then discusses the fossil evidence that support both phyletic gradualism and punctuated equilibrium. The paper concludes that it would seem that the theory of punctuated equilibrium would seem more appropriate to explain what we observe as the results of macroevolution.

Table of Contents:
Introduction
Debate between Phyletic Gradualism and Punctuated Equilibrium
Fossil Evidence that support both Phyletic Gradualism and Punctuated Equilibrium
Opinion

From the Paper:

"A second example involves Melanopsis fossilis and Melanopsis vindobensis, melanopsis belongs to a species of freshwater mollusk. Several intermediates were found between the two. The presence of the intermediates gave rise to the question whether this was an example of gradualism. (Geary 1992) However, since gradualism theorizes that speciation takes place at the level of a population and not the individual, this notion was defeated because the parent, daughter and intermediates were all found in the same river beds, in the sediment. Researchers theorized that the intermediates were really hybrids between the parent and daughter species."

Sample of Sources Used:

• Eldredge, N., and S. J. Gould. "Punctuated Equilibria: An Altenative to Phyletic Gradualism." Models in Paleobiology. Ed. Thomas J. M. Schopf. San Francisco,: Freeman, 1972. 82-115.
• Geary, D.H. . "An Unusual Pattern of Divergence between Two Fossil Gastropods: Ecophenotypy, Dimorphism or Hybridization." Paleobiology 18 (1992): 93-109.
• Jackson, J. B. C., and A. H. Cheetham. "Phylogeny Reconstruction and the Tempo of Speciation in Cheilostome Bryozoa." Paleobiology 20 (1994): 407-23.
• Mayr, Ernst. Populations, Species, and Evolution; an Abridgment of Animal Species and Evolution. Cambridge, Mass.,: Belknap Press of Harvard University Press, 1970.
• Nehm, R.H., and D.H. Geary. "A Gradual Morphologic Transition During a Rapid Speciation Event in Marginellid Gastropods " Journal of Paleontology 68 (1994): 787-95.

More papers on Theories of Evolution:

• Essay # 25235 : "The Role of Natural Selection in the Theory of Evolution"
• Argumentative Essay # 98431 : "God and the Theory of Evolution"
• Term Paper # 141782 : "Darwin's Theory of Evolution: Compatibility With Design"

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