Quantum evolution is a component of George Gaylord Simpson's
multi-tempoed theory of evolutionary change, responsible for the
rapid emergence of higher taxonomic groups. According to
Simpson, evolutionary rates differ from group to group and even
among closely related lineages. These different rates of
evolutionary change were designated by Simpson as horotelic
(medium tempo), bradytelic (slow tempo), and tachytelic (rapid
tempo). Quantum evolution differed from these styles of change
in that it involved a drastic shift in the adaptive zones of
certain classes of animals. The word "quantum" therefore refers
to an "all-or-none reaction," where transitional forms are
particularly unstable, and perished rapidly and completely.
Although Quantum evolution may happen at any taxonomic level
(1953, 389), it plays a much larger role in "the origin
taxonomic units of relatively high rank, such as families,
orders, and classes." (1944, 206) According to Simpson (1944)
quantum evolution relied heavily upon Sewall Wright'