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Keywords:

  • Speriation;
  • morphological stasis;
  • punctuated equilibria;
  • fossil molluscs -cichlid fishes;
  • African lakes

Fryer, Greenwood & Peake (1983) have recently criticized my analysis of morphological variation in a sequence of Plio-Pleistocene freshwater molluse faunas from the Turkana Basin in E Africa, and question my conclusions that these faunas document speciation and the punctuated equilibrium model of evolutionary change. Unfortunately, these authors misinterpret the nature of the phenotypic variation in African freshwater molluscs and its relevance to my study, and apparently misunderstand punctuated equilibrium theory. Although the majority of their criticisms are therefore erroneous, certain of the points they raise are important: they are addressed here.