The Evolution of Shribbles

 

Subject Area

 Biology - Evolution

Age or Grade

 Introductory Biology – Grades 9 +

Estimated Length

 2 hours

Prerequisite knowledge/skills

 Students should be familiar with the concept of natural selection, mutation, and heredity.

Description of New Content

 This laboratory activity is intended to illustrate the concept of natural selection in a hands-on way. While no brand new content is introduced, students will gain an increased understanding of the mechanisms of evolution, including natural selection, mutation, and sexual selection (an extension).

Goals

To illustrate the mechanism of natural selection in a hands on and easy to understand manner.

Materials Needed
  1. Beads of 3 or 4 different colors represent “shribbles” with different coat colors, and one color for grass or rocks or some other aspect of the environment
  2. Construction paper with colors matching some of the beads
  3. Scissors + tape to make construction paper containers

 

Procedure

 

 

 

Setup :

4.      Each group of 2-4 students receives containers and differently colored beads

5.      “Hunting” for beads proceeds under the instruction of the teacher, who times each hunt

6.      Students record results in lab notebooks

Experimental procedure:

7.      Initial Shribble population: 10 pink and 10 clear Shribbles in a white box, living among shrubbery (green beads)

8.      Students hunt for Shribbles using the following instructions

1.      Hunter: Close your eyes.

2.      Agitator: Mix all the beads, agitate the box by shaking it lightly

3.      Hunter: Open your eyes and try to catch as many Shribbles as possible, only ONE SHRIBBLE AT A TIME

4.      Hunt for 3 seconds

9.      Shribbles reproduce to repopulate the group as follows

1.      Every other Shribble has a child of the same color

2.      New population is “Generation 2”

10.  Students repeat the hunt with Generation 2 and Generation 3

Post Lab:

11.  Students perform calculations with the data to generate graphs of shribble populations before and after each hunt as a function of coat color

  1. Students answer questions about the experiment: Describe the results shown in each graph. What happened to Shribles of each color as they continued to be hunted through the generations?
    1. Why did Shribles of one color survive better than those of the other?
    2. Imagine this hunting continued for another ten generations. Would you expect to see any Shribles with pink fur left in the population at the end? Why or why not?
    3. How does this laboratory demonstrate the mechanisms of Evolution by Natural Selection?
    4. Now, imagine a population of only pink Shribles, living in a white paper box. Occasionally, some Shrible babies are born with clear fur instead of pink. The ones that have clear fur then go on to have babies with clear fur. After 10 generations, what would you expect the population to look like? Would you expect all pink Shribles, the way it began? A mix? All clear ones? Explain your predictions using the concepts of Evolution illustrated in this laboratory.
    5. Imagine a mixed population of Shribles, half with pink fur and half with clear fur living in a white paper box. Suddenly, their habitat is flooded with pink water, and their box becomes pink forever. This does not disturb the hunters, who continue to look for dinner as before. What do you expect the population of Shribles to look like after 3 generations? Pink, clear, or mixed? Explain your prediction using the concepts of Evolution illustrated in this laboratory.

 

 

 

Evaluation

Students will be graded based on class participation, the quality of their data collection, and the quality of their lab report, which includes calculations and answers to the post lab questions posted above

Extensions

 Questions 4 and 5 could be turned into separate experiments to illustrate the effect of mutation and environmental changes on evolution. The concept of sexual selection can also be applied to this exercise: for instance, shribble populations reproduce based on mate preference, where more brightly colored shribbles are preferred and produce many more offspring than neutrally colored ones. The students can make predictions over which force will guide the evolution of the population: the ability of the neutrally colored shribbles to hide from hunters, or the ability of brightly colored ones to produce many offspring.

References

 Evolution of Shribbles handout, “Modern Biology” Textbook, Wikipedia