Macroevolution

Macroevolution is evolution on a scale of separated gene pools. Macroevolutionary studies focus on change that occurs at or above the level of species, in contrast with microevolution, which refers to smaller evolutionary changes (typically described as changes in allele frequencies) within a species or population. Macroevolution and microevolution describe fundamentally identical processes on different time scales.

The process of speciation may fall within the purview of either, depending on the forces thought to drive it. Paleontology, evolutionary developmental biology, comparative genomics and genomic phylostratigraphy contribute most of the evidence for the patterns and processes that can be classified as macroevolution. An example of macroevolution is the appearance of feathers during the evolution of birds from theropod dinosaurs, when now viewed at a distance from the future, although as they arose the developing changes would be deemed microevolution.

The evolutionary course of Equidae (wide family including all horses and related animals) is often viewed as a typical example of macroevolution again from the broad viewpoint after a notable accumulation of previously microevolutionary changes. The earliest known genus, Hyracotherium (now reclassified as a palaeothere), was a browsing herbivore animal resembling a dog that lived in the early Cenozoic. The preferred evolutionary explanation is that as its habitat transformed into an open arid grassland (which we can reconstruct through pollen and seed records), selective pressure acted so that the animal become a fast grazer (as recorded by dentition changes etc.). Thus elongation of legs and head as well as reduction of toes gradually occurred, producing the only extant genus of Equidae, Equus.