Rates Of Evolution: Phyletic Gradualism VS Phyletic Equilibrium

Punctuated equilibrium can be contrasted with evolution by phyletic gradualism,
in which evolution occurs at a constant rate. Eldredge and Gould claim that this
hardly ever happens and the dispute between the two theories is one of the
most important in evolutionary biology.

Figure: the crucial difference between punctuated equilibrium and phyletic

gradualism concerns the rate of evolution at, and between, splitting events. (a)

punctuated equilibrium; (b) phyletic gradualism. On a strict interpretation of

punctuated equilibrium, sudden change without splitting (c) contradicts the

theory.