How do gradualism and punctuated equilibrium differ in evolutionary tempo?

How do gradualism and punctuated equilibrium differ in evolutionary tempo?

• A. Gradualism posits slow, steady accumulation of changes; punctuated equilibrium suggests long periods of little change interrupted by rapid speciation events
• B. Gradualism involves rapid, large changes over short time spans
• C. Punctuated equilibrium predicts no long-term changes
• D. Punctuated equilibrium cannot involve reproductive isolation

Answer: (A)

Tempo of evolution is being tested—how evolutionary change occurs over time. Gradualism and punctuated equilibrium describe two different patterns of that tempo. Gradualism envisions slow, steady accumulation of small changes over long periods. Punctuated equilibrium, on the other hand, predicts long stretches of little change (stasis) that are interrupted by relatively rapid bursts of change during speciation events. This fits with fossil records showing sudden shifts after long periods of little apparent change. That idea is reflected in the correct statement: evolution tends to proceed slowly and steadily most of the time, with occasional rapid changes when new species arise. The other options conflict with what we observe about evolutionary tempo, such as asserting rapid, large changes over short spans, denying long-term change, or claiming punctuated equilibrium cannot involve reproductive isolation.

Tempo of evolution is being tested—how evolutionary change occurs over time. Gradualism and punctuated equilibrium describe two different patterns of that tempo.

Gradualism envisions slow, steady accumulation of small changes over long periods. Punctuated equilibrium, on the other hand, predicts long stretches of little change (stasis) that are interrupted by relatively rapid bursts of change during speciation events. This fits with fossil records showing sudden shifts after long periods of little apparent change.

That idea is reflected in the correct statement: evolution tends to proceed slowly and steadily most of the time, with occasional rapid changes when new species arise. The other options conflict with what we observe about evolutionary tempo, such as asserting rapid, large changes over short spans, denying long-term change, or claiming punctuated equilibrium cannot involve reproductive isolation.