"The Eldredge-Gould concept of punctuated equilibria has gained wide acceptance among paleontologists. It attempts to account for the following paradox: Within continuously sampled lineages, one rarely finds the gradual morphological trends predicted by Darwinian evolution; rather, change occurs with the sudden appearance of new, well-differentiated species. Eldredge and Gould equate such appearances with speciation, although the details of these events are not preserved. ...The punctuated equilibrium model has been widely accepted, not because it has a compelling theoretical basis but because it appears to resolve a dilemma. Apart from the obvious sampling problems inherent to the observations that stimulated the model, and apart from its intrinsic circularity (one could argue that speciation can occur only when phyletic change is rapid, not vice versa), the model is more ad hoc explanation than theory, and it rests on shaky ground."
Ricklefs, Robert E., "Paleontologists Confronting Macroevolution," Science, vol. 199, 1978, p. 59
Robert E Ricklefs is an evolutionist and professor biology at the University of Missouri te St. Louis:
http://www.umsl.edu/~ricklefs