What is the name of the hypothesis that evolution occurs at a slow constant rate?

Darwin's classic theory of evolution assumed that evolution is a slow, contunuous process, by which new species evolve and emerge. This is referred to at times as "organic evolution" and the "synthetic theory of evolution", or just the Darwinian theory of evolution. A newer theory, proposed originally by Niles Eldridge and Stephen Jay Gould is known as "punctuated equilibria", a model in which the evloution of new species occurs only periodically, in relatively rapid spurts. See "Time Frames the Rethinking of Darwinian Evolution and the Theory of Punctuated Equilibraia, Simon & Schuster, 1985"

Answer

The slow, constant process has also been called "gradualism."