16 3 Darwin Presents His Case by 08c5mV

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									Name                                                        Class           Date




16.3 Darwin Presents His Case
Lesson Objectives
       Describe the conditions under which natural selection occurs.
       Explain the principle of common descent.


    BUILD Vocabulary
A. The chart below shows key terms from the lesson with their definitions. Complete the chart by
   writing a strategy to help you remember the meaning of each term. One has been done for
   you.

 Term              Definition                           How I’m Going to Remember the
                                                        Meaning
 Adaptation        An inherited characteristic that
                   increases an organism’s ability to
                   survive


 Fitness           How well an organism can             I know it is important for me to be
                   survive and reproduce in an          physically fit so I can live longer. Fitness
                   environment                          is how well an organism can survive.


 Natural           The process by which organisms
 selection         that are most suited to their
                   environment survive and
                   reproduce



B. As you work through this lesson, you may find these terms in the activities. When you need to
   write a key term or a definition, highlight the term or the definition.

    BUILD Understanding
Preview Visuals Before you read the lesson, preview the diagram that shows the process of
natural selection. Describe what the visual helps you understand in the right column of the table
below.


                  Description                              What It Helps Me Understand

 Natural selection in grasshoppers




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Name                                                        Class         Date



Evolution by Natural Selection
An adaptation is an inherited characteristic that helps an organism survive and reproduce in its
environment. Over time, adaptations become more and more common in the population. For
example, suppose that the water in a pond gets darker over a period of four years. The diagrams
and table below show what might happen to a frog population living in the pond.
Use the diagrams below to complete the table.

         Year 1                    Year 2                    Year 3                 Year 4




                        Adaptations of Frog Populations Over Time

             Year                     Light-Colored Frogs               Dark-Colored Frogs
               1                                  6

               2

               3
               4


Answer the questions.
 1. In which year was the number of light-colored frogs greater than the number of dark-colored
    frogs?
 2. How did the numbers of light- and dark-colored frogs change over time?


 3. Which adaptation is best suited to life in the pond in Year 3? Circle the answer.
    light coloring                dark coloring
 4. How do the dark-colored frogs show “survival of the fittest”?




 5. How is natural selection different from artificial selection?




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