Final answer:
Evolution can occur gradually or in sudden bursts. Gradualism proposes that evolution happens slowly over time, while punctuated equilibrium suggests that rapid changes occur during periods of environmental change.
Step-by-step explanation:
The process of evolution can occur in two ways, either gradually or in sudden bursts. Gradualism is the model proposed by Darwin, where evolution occurs slowly and continuously over long periods of time when geologic and climatic conditions are stable. However, the fossil record better supports the model of punctuated equilibrium, which suggests that evolution can also occur more quickly during periods of rapid environmental change. These bursts of evolution fill open niches created by sudden changes. Both gradualism and punctuated equilibrium are important factors in the process of evolution.