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Phyletic gradualism vs. punctuated equilibrium: applicability of neontological data

  • Robert E. Ricklefs (a1)


An equation for the distribution of divergence times between closest relatives is derived to explore the possibility that contemporary data might shed some light on the controversy between supporters of gradual versus punctuated phyletic change. The principal assumptions of the model are uniform rates of speciation and extinction, bifurcating speciation, and uniform patterns of divergence, by whatever measure, among species in a taxon. The structure of the model indicates clear differences between patterns generated by extremes of gradualism and punctuation. But inability to verify critical assumptions considerably weakens the applicability of the model to the gradualism-punctuation problem.



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Gould, S. J. and Eldredge, N. 1977. Punctuated equilibria: the tempo and mode of evolution reconsidered. Paleobiology. 3:115151.
Pielou, E. C. 1977. Mathematical Ecology. John Wiley; New York.


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