punctuated equilibrium
a theory of evolution proposing that periods of rapid change, resulting in the development of new species, are separated by longer periods of little or no change. Proposed in 1972 by U.S. paleontologists Niles Eldredge (1943– ) and Stephen Jay Gould (1941–2002), the theory subsequently inspired similar models of change as applied to other processes. In a model of group development, for example, U.S. behavioral scientist Connie J. Gersick proposed in 1988 that groups go through three stages of development: (a) a preliminary stage of setting deep structures (i.e., establishing how the group will be organized and what activities it will carry out); (b) an equilibrium period during which the deep structures are maintained; and (c) a revolutionary period of rapid change (usually resulting from environmental pressures) during which the deep structures are undone and superseded by new ones.