Final answer:
Punctuated equilibrium describes periods of evolutionary stability interrupted by quick changes. It contrasts with gradualism, which suggests continuous slow change over time. Both processes have left evidence in the fossil record and contribute to species evolution.
Step-by-step explanation:
The term punctuated equilibrium refers to long periods of stability, with occasional evolutionary steps. This concept proposes that species remain relatively unchanged for extensive periods, known as stasis, which are punctuated by rapid periods of evolutionary change. Unlike the gradual model of evolution, called gradualism, which suggests a slow and continuous process, punctuated equilibrium is characterized by abrupt changes in species due to a variety of environmental factors, such as climate change, that create new evolutionary pressures and opportunities. In the fossil record, we often observe static populations that are interrupted by these sudden bursts of change, supporting the theory of punctuated equilibrium. However, the presence of intermediary forms in the fossil record also indicates that gradualism plays a role in the evolutionary process. Studies have shown that a mix of both sudden and gradual changes contributes to the speciation events that shape the evolutionary history of life on Earth. Species evolution is neither linear nor wholly progressive; it's more like a branching tree with divergence points and shared ancestry.