California Science Test (CAST) Practice Exam

Gradualism is the idea that evolution occurs slowly but steadily over many generations. It envisions small, incremental genetic changes accumulating over long time spans, with natural selection acting on each small variation to shape species gradually. This contrasts with punctuated equilibria, which proposes long periods of little change interrupted by brief bursts of rapid evolution. The other terms don’t describe the pace of evolution—extinct refers to a species no longer existing, and habitat is the environment where a species lives.