UCMP Lessons  

Preying on Beans

Author: Jolene Routson

Overview: Students act as predators searching for prey (beans) in two different settings to demonstrate the processes of adaptation and selection.

Lesson Concepts:

Grade Span: 3–5


Advance Preparation:

— At the market, select four colors of beans of about the same size.
— Mix the four types of beans together and distribute them in the designated search areas. It is best to have areas cordoned off prior to the distribution.
— Data table for each student to record number and color of prey caught.

Time: 50–60 minutes

Grouping: Solo or pairs

Teacher Background:

Natural selection is one of the basic mechanisms of evolution. Darwin's grand idea of evolution by natural selection is relatively simple, but often misunderstood. For example, imagine a population of beetles. Some are greenish and some are brownish, and these different colors are the result of inherited traits. Since the environment cannot support unlimited population growth, not all beetles get to reproduce to their full potential. Let us suppose that in this example the greenish beetles tend to get eaten by birds and therefore have less chance to reproduce. (This is called differential reproduction.) The surviving brownish beetles have an advantageous trait, which allows them to produce more offspring. The brownish color will become more common, and if the trend continues, all beetles in that population will eventually be brown.

Explore these links for additional information on the topics covered in this lesson:

Teaching Tips:

The concept of natural selection may be difficult for younger students to grasp in its entirety. However, the main objective should be to understand that those individuals that blend with their environments will be less likely to be caught by predators. More of the "blenders" tend to survive and therefore have an opportunity to reproduce.

Thirty seconds search time is suggested, however you may choose to vary the amount of time to accommodate your students. Predators should not have enough time to catch all of the prey.

It is helpful to create a data table for students to record how many of each color of prey (bean) was collected. Students can make graphs from their own data tables.

Vocabulary: predator, prey, survival, reproduction, and natural selection


  1. Set the scene by telling the students that they are going to play the role of predator animals. The prey animals are represented by beans on the floor.
  2. Tell the students (predators) that they will have three minutes to capture as many beans (prey) as they can.
  3. Students should place their captured beans in a small bag or paper cup.
  4. At the end of the time limit, students will return to their seats to count up their prey and record their results.
  5. Have students graph their results. The type of graph may vary depending on the age group. However, a basic bar graph depicting the three types of beans is sufficient.
  6. Discuss and compare graphs.
  7. Repeat the procedure, steps 2–6 on the lawn.
  8. Pose questions such as: Was there a difference between the results on the floor and in the lawn? What might be the reason for the differences in results? Which beans (prey) were difficult to find? Which were the easiest? How do the beans compare to real animals found in the wild? Why do you think it would be beneficial to blend with your environment? Why do animals that blend with their environment (or are hard to see) have an advantage over those who do not blend in? How does your graph compare with others in the class?


There are many variations of this activity. For example, colored toothpicks can be used instead of beans or colored hole punches on patterned fabric. Note: colored toothpicks in a lawn are an excellent way to do this activity, but leftover toothpicks in the lawn may present a hazard. Colored pasta is another potential option.

Updated November 19, 2003

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