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define: gradualism A model of evolution that assumes slow, steady rates of change. Charles Darwin's original concept of evolution by natural selection assumed gradualism. Contrast with punctuated equilibrium.

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• Evolution has a fairly constant rate. • New species arise by the gradual transformation of ancestral species. • The rate of evolution during the origin of new species is much like that at any other time.

For gradualists, the fact that fossil evidence shows species suddenly appearing with little signs of any transitional forms is due to the incompleteness of the fossil record. There is a historical controversy as to whether Darwin himself was committed to gradualism. It is most likely that he was a gradualist about the evolution of adaptations, not about the pattern of evolutionary rates.

contrast with: punctuated equilibrium a theory of evolution holding that evolutionary change in the fossil record came in fits and starts rather than in a steady process of slow change