The term for the gradual evolution of species over time is known as phyletic gradualism. This concept posits that species evolve through a slow and constant process of change, resulting in gradual modifications of their characteristics. Phyletic gradualism suggests that evolutionary change occurs in small increments, leading to the eventual emergence of new species. This concept contrasts with the theory of punctuated equilibrium, which proposes that evolutionary changes occur in bursts, separated by long periods of stability.