An addition to the neo-Darwinian theory of evolution proposed by paleontologists Stephen Jay Gould and Niles Eldredge in 1972, punctuated equilibrium is intended to explain the lack of intermediate steps in fossil records. Gould and Eldredge propose that biological species do not evolve gradually (as in gradualism) but exist in a state of stable equilibrium (stasis) with no or very slow evolution followed by a burst of fast evolution that quickly, by geological timescale, results in the formation of new species. Gould and Eldredge also suggest that not all evolutionary changes are adapted (as in adaptationism) and that some evolution occurs at the level of species. Punctuated equilibrium is sometimes confused with saltationism, evolution by sudden large changes due to macromutations.

See also CATASTROPHISM; EVOLUTION; GRADUALISM

ARN O. GYLDENHOLM