What term describes the idea that species evolve slowly and continuously over long periods of geological time?

The term that describes the idea that species evolve slowly and continuously over long periods of geological time is gradualism. Gradualism suggests that evolutionary changes happen in small, incremental steps rather than in sudden, large shifts. This concept emphasizes that the process of evolution is a slow and steady accumulation of changes in a population that ultimately leads to the development of new species over extensive timeframes.

In contrast, adaptation refers to the process through which a species becomes better suited to its environment, which may occur in both gradual and more rapid forms, depending on circumstances. Speciation is the process by which new species arise, often as a result of evolutionary changes, but it does not specifically describe the speed or nature of those changes. Mutation involves random changes in an organism's DNA, which can contribute to genetic diversity and the raw material for evolution, but it does not encapsulate the overall process of gradual evolutionary change over geological time.