- A Both punctuated equilibrium and gradualism are sometimes considered largely identical evolutionary models, despite the two models differing sharply in predicting stasis-with-bursts versus continuous change in standard practice
- B Punctuated equilibrium (Gould and Eldredge, 1972): evolution consists of long periods of stasis (little change) punctuated by rapid speciation events; contrasts with gradualism (Darwin's view) of continuous gradual change
- C Punctuated equilibrium is sometimes thought to mean evolutionary change does not occur within any lineage, when in fact it describes long stasis interrupted by rapid bursts of speciation under most conditions encountered
- D Gradualism as originally proposed by Darwin is sometimes thought to be comprehensively disproven by the fossil record, when in reality it remains a valid complementary model some lineages follow as frequently observed in practice
Correct answer: B. Punctuated equilibrium (Gould and Eldredge, 1972): evolution consists of long periods of stasis (little change) punctuated by rapid speciation events; contrasts with gradualism (Darwin's view) of continuous gradual change
Explanation: Gradualism (Darwin): evolution proceeds by slow, steady, continuous change. Punctuated equilibrium (Gould, Eldredge): fossil record shows: (1) Long periods of stasis (unchanged for millions of years); (2) Rapid transitions (geologically) when change occurs; (3) New species appear suddenly in fossil record; (4) Can be explained by allopatric speciation of small peripheral populations (too small to leave fossil record) followed by invasion of range. Both modes likely occur in evolution.
Concept context
Origin of life, Darwin's theory, natural selection, speciation, and evidence for evolution.