Tachytely

tachytely [¦tak·ə¦tel·ē]

(evolution)

Evolution at a rapid rate resulting in differential selection and fixation of new types.

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Tachytely 

a very rapid rate of evolution over a relatively short period of time, characteristic of certain groups of organisms; the term was coined by G. G. Simpson in 1944. The formation of a new family, for example, of mammals, requires tens of millions of years on the average, but for some groups—those exhibiting tachytely—the process has been completed within a few million years. Abrupt and frequent changes in the environment are assumed to be the most important factors responsible for tachytely. Tachytelic groups later quickly become bradytelic or horotelic, or they become extinct.