Which term describes the evolution of species in a gradual manner over long periods?

The term that describes the evolution of species in a gradual manner over long periods is Gradualism. This concept suggests that evolutionary change occurs slowly and steadily, with small, incremental changes accumulating over vast stretches of geological time. It contrasts with the idea of sudden shifts or rapid changes in species, implying that species evolve through a continuous process of variation and selection.

Gradualism emphasizes the importance of gradual adaptations to environmental changes or selective pressures that lead to the development of new traits over generations, ultimately resulting in the formation of new species. This approach aligns with the fossil record, which often shows transitional forms that illustrate gradual change.

The other options refer to different evolutionary processes. Divergent evolution involves species that develop different traits as they adapt to different environments from a common ancestor. Convergent evolution describes how unrelated species develop similar traits due to facing similar environmental challenges. Instantaneous evolution, while less commonly used in evolutionary biology, suggests rapid changes in a population, which is not aligned with the long-term gradual changes emphasized by gradualism.