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quantum evolution[′kwän·təm ‚ev·ə′lü·shən]
a form of evolution of a group of organisms that is related to abrupt transition from one adaptive zone to another.
The term “quantum evolution” was introduced by the American biologist G. G. Simpson in 1944. In this sense “quantum” is an effect that, when lower than a given threshhold, produces no reaction but, passing the threshhold, alters the equilibrium and (through the operation of harsh natural selection) leads the group either to extinction or to distinct structural modifications and the appearance of new families, orders, suborders, and so forth. Quantum evolution explains the explosive character of the evolution of many large groups of organisms that seemed to flourish suddenly. Thus, the formation of vast plains at the beginning of the Tertiary period and the appearance of herbaceous angiosperms (especially Gramineae) contributed to progressive modifications in the structure of the dental system, skull, and extremities of ungulates; this in turn led to an abrupt change in the number, diversity of form, and universal dispersion of the group.
REFERENCESimpson, G. G. Tempy i formy evoliutsii. Moscow, 1948. (Translated from English.)
A. V. IABLOKOV