Which theory suggests that evolution occurs through small changes over a long period of time?

The theory that suggests evolution occurs through small changes over a long period of time is known as gradualism. This concept posits that species evolve continuously and incrementally, highlighting the slow and steady nature of evolutionary change. Gradualism implies that these small, gradual changes accumulate over extensive periods, ultimately leading to significant differences that may result in the formation of new species.

In contrast to this, punctuated equilibrium proposes that evolution occurs in relatively quick bursts of change, followed by long periods of stability. This theory emphasizes that most species show little change for most of their geological history, but when they do change, it happens rapidly in response to significant environmental shifts.

Divergent evolution refers to the process where related species evolve different traits due to adapting to different environments. Adaptive radiation is a form of divergent evolution where a single ancestor species rapidly diversifies into a wide variety of forms to adapt to various ecological niches. Both of these concepts deal with how species can change or diversify but do not specifically address the gradual process of evolutionary change over long periods as gradualism does.