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Copyright © 1997, Jay Ligda.  All rights reserved.  Published by Humans in the Universe and Jay Ligda.

Punctuated Equilibrium

      Punctuated equilibrium is the argument against gradual change in the evolutionary process as Darwin stated it.  Stephen Gould and Niles Eldredge (as cited in Rensberger, 1983) put forth the hypothesis that evolutionary change doesn't happen gradually, but rather it happens suddenly.  A species enjoys long periods without any evolutionary change and then "suddenly" (over a period of several hundreds to several thousands of years) evolved into a new species.  The evidence that supports punctuated equilibrium is in the fossil records.  There is very little evidence of gradual change in most species in the fossil record, rather "in most cases species simply appear at a given time, persist relatively unchanged for a few million years and then disappear" (Rensberger, 1983, p.2).  Margulis and Sagan (1986) note that the appearance of the nucleus in the evolution of a cell "looks as drastic as if the Wright Brothers' Kitty Hawk flying machine had been followed a week later by the Concorde jet" (p. 115).

      Arguments against punctuated equilibrium state that the fossil record is too scant to show any transitional forms.  Further, gradual change may occur in the soft tissue of a given species.  Soft tissue change would not be evident in the fossil record.  Also, there does appear in some of the fossil records a gradual change, but in most cases there doesn't (Rensberger, 1983).

      Alan C. Wilson (as cited in Rensberger, 1983) of the University of California at Berkeley concludes that evolution is slow and gradual for most species, faster and more abrupt for others.  Leigh Van Valen (as cited in Rensberger, 1983) of the University of Chicago doesn't support either of these view points: "I don't think the evidence is good enough to resolve the issue" (p. 5).  He believes there is probably a range of evolutionary rates.

by Jay Ligda

(This work is a all or part of an original work first published/written for John. F. Kennedy University:  Final Integrative Project., Mar1996.)


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References

  • Margulis, L. & Sagan, D. (1986).  Microcosmos:  Four Billion Years of Microbial Evolution.  New York, NY:  Summit.
  • Rensberger, B.  (1983).  The evolution of evolution.  in W. Kornberg (Ed.)  NSF mosaic reader: Evolution, new perspectives.  pp. 1 - 9.  Wayne, NJ: Avery.

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