The Species Problem


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This is my attempt to explain punctuated equilibrium vs. phyletic gradualism and how both ideas contribute to the controversy of what constitutes a species.

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The Species Problem

  1. 1. The Species Problem How it Affects Paleontology ““The boundaries of the species, wherebymen sort them, are made by men.”- John Locke
  2. 2. What is a Species?• A species is “the fundamental taxonomic unit in nature” (39.)• Species “recognize each other.”• Proof of this “recognition” is displayed in reproductive habits, or the potential for interbreeding.
  3. 3. Species of Lilies
  4. 4. Variation in a Single Butterfly SpeciesKingdom - AnimaliaPhylum - ArthropodaClass - InsectaOrder – LepidopteraFamily- Nymphalidae SpeciesGenus-Agrias Agrias
  5. 5. What is phylogeny?Loosely (according to the dictionary) phylogeny is the evolutionary history of agroup of organisms as depicted in their family tree or “cladogram.”
  6. 6. A Basic Cladogram
  7. 7. Two Concepts of Species (p 39)• Morphological • Biological Species Species  Population array Diagnosible cluster  Actual Pattern of ancestry interbreeding Self contained OR group  Potential “beyond which interbreeding there is not”  Reproductive (Eldredge and Cracraft) isolation
  8. 8. These opposing ideas break intotwo camps: Phyletic Gradualism Punctuated Equilibrium• Often favored by • Makes more sense in biologists and life the context of scientists paleontological• Speciation is studies slow, uniform and • Most species exhibit gradual little net evolutionary change
  9. 9. A paleontologicalstudy of speciationin favor of phyleticgradualism.
  10. 10. Scientists Today…-Tend to adhere to a biological concept of species.-This can pose a problem for Paelontologists.
  11. 11. There are at least 24 different species concepts and none of them can be applied to all organisms that have ever lived. (Hey, J. 2001 qtd in Techne)
  12. 12. How do Paleontologists Know?• Fossils cannot demonstrate interbreeding or the lack thereof.• Therefore, typological (morphological) species divisions make the most sense.
  13. 13. Potential Problems Sexual Dimorphs Ontogeny (developmental stages)Recent reconstruction of Pterodactyls
  14. 14. Modern Sexual Dimorphs
  15. 15. Modern Insect Ontongeny
  16. 16. Is Time on our Side? Paleontologists have adifferent perspective than biologists.
  17. 17. TIME Key Wordanagenesis-gradually changing from one form to another
  18. 18. Determining a “Cut Off”GAPS IN RECORD VS CONTINUOUS SERIES• Artificial  First Specimen?• Convenient  Halfway through? New Problem: Pseudoextinction
  19. 19. What is “Pseudoextinction?”• Parent species go extinct as new species evolve in succession• Not the same as extinction.• Part of the evolutionary species concept.
  20. 20. Trilobite Family Tree
  21. 21. Take your Pick! • General paleontologists will find the evolutionary species concept (a lineage that evolves separately with separate lineages and• Biostratigraphers tendencies) more make use of many practical fine species divisions to date layers of stratigraphy.
  22. 22. A Solution to the Mayhem Punctuated Equilibrium to the Rescue!• Phyletic gradualism(gradual transformation among species) is actually not that common in the fossil record.• Actually, fossil records appear to remain static and relatively unchanged throughout paleo reconstructions for the most part.
  23. 23. Punctuated Equilibrium• Most large species populations do not evolve in any direction.• Fossil populations remain in stable equilibrium for long periods,• Punctuated by the introduction of a new species formed in an isolated area (and then migrated back to main group.)
  24. 24. Eldredge and Gould Stephen J. Gould Niles EldredgeThere is very little proof of anagenetic transformations taking place.
  25. 25. Exception:Biostratigraphy
  26. 26. Exception:George Simpson of ColumbiaUniversity says,“The state of rest is the exceptionand it seems that some restraintor force must be required tomaintain it."
  27. 27. Main IdeaAnagenetic continua are rare, and thus species division is not as complicated as it seems.Nietzche says, “Out of chaos comes order.”Punctuated Equilibrium simplified the species problem significantly.
  28. 28. Sources:"Biostratigraphy." Harvard University Museum of Comparative Zoology. Harvard University, 2004. Web. 7 Sep 2011. < ton/Intro/GeologyPage/Sedimentary%20Geology/biostrat.htmCrampton, , James. Gale, A. "A plastic boomerang: speciation and intraspecific evolution in the Cretaceous bivalve Actinoceramus." Paleobiology 31.4 (2005): 559-577. BioOne. Web. 7 Sep 2011. <>.Phylogeny. (2012, April 14). Retrieved from www.dictonary.comProthero, Donald. Bringing Fossils to Life. 2nd ed. NY: McGraw-Hill, 2004. 39-45. Print.Punctuated Equilibrium." Wikipedia. Online. 2011. Print. <>.Unknown. (Image Creator). (2012). Phylogenetic tree of life. [Print Photo].Retrieved from