Macroevolutionary changes are driven by mechanisms such as natural selection, mutation, migration, and genetic drift. Evidence for macroevolution—for the processes that shaped higher level groups of organisms—exists in the fossil record as well as in the genetic material and developmental processes of living organisms. Given enough time, small changes accumulate and result in large evolutionary changes.
To better understand what macroevolution is, it helps to contrast it with microevolution. Microevolution is another type of biological evolution but it differs from macroevolution in that its primary focus is not large-scale evolutionary processes but smaller-scale processes. Microevolution examines evolutionary changes within a single population—a group of organisms that interbreed and therefore all belong to the same gene pool.