3.3 Gradualism and Punctuated Equilibrium
Completion requirements
Unit B
Module 4 ~ Lesson 3
The Pace of Evolution
Darwin's theory of evolution by natural selection remains the basis of many people's understanding of evolution. However, scientific debate about the pace of evolution continues. Modern-day scientists propose two models: gradualism and punctuated equilibrium. Although both models use the theory of evolution by natural selection, they have some key differences.Gradualism
Evolutionary biologists who support the model of gradualism explain evolution as a slow and gradual process with new species appearing as a result of many small changes over long periods of time. The fossil record rarely shows these small changes; however, not all changes are present in the fossil record.
Punctuated Equilibrium
Those who support the model of punctuated equilibrium suggest that evolutionary change occurred in the same way that it appears in the fossil record; suddenly. This model proposes periods of equilibrium with very little change in a species punctuated by periods of rapid change.
Read
Read "The Pace of Evolution" on pages 140 to 141 of your textbook.
Inquiry into Biology u2_p.150, from McGraw Hill. Reproduced by permission.