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Module 4 Intro

1. Module 4 Intro

1.13. Page 4

Lesson 2

Module 4—Mechanisms of Population Change

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Two models for evolution are shown in this combined diagram. The left diagram looks like a tree branch. Each new branch indicates divergence, and the new species arises in the middle of the new branch. The right diagram looks like a family tree. New species branch out at 90-degree angles. There is divergence at the beginning of the branch and a new species indicated at the end of the 90-degree branch.

Inquiry into Biology u2_p.150, from McGraw Hill Reproduced by permission.

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. Read “The Pace of Evolution” on page 140 in the textbook.

 

gradualism: gradual change occurs in a steady, linear way over time

 

punctuated equilibrium: evolutionary history is said to consist of long periods of equilibrium, interrupted by periods of speciation

 

 


 
Try This

 

TR 3.  The Pace of Evolution

 

You will look at which theory—in your opinion—best explains evolution. You will also compare and contrast gradualism with punctuated equilibrium. Go to your Module 4: Lesson 2 Assignment to answer the questions for this Try This activity.