Key concepts
Traits
Generations
Natural selection

From National Science Education Standards: Organisms and environments

Introduction
Have you ever wondered why some animals are so well camouflaged in their environments? Have you ever seen a walking stick? It's an insect that looks just like a twig! How did it come to look so much like a stick? If walking sticks lived on sandy surfaces, would they be as hidden from their predators?

In different environments, certain appearances are more useful than others, especially when hiding from predators. For instance, an insect hiding on tree bark might look very different from one that is hiding on a leaf. What colors would be best for each of these bugs?

Background
Over millions and millions of years, all of the different species have come to look and act the way they do through a process called evolution by natural selection. Because this process is so slow, it is often difficult for people to imagine how it works. The main premise is very simple, however: individuals with certain characteristics, or traits, are better adapted to live successfully in their environment. Individuals with these traits live longer and have more offspring, thus increasing the chance that their traits are handed down to future generations.

As a result of living and having offspring in different environments, different populations develop varied appearances over time. Today we will explore the idea of evolution by natural selection and will simulate how a population can change over time.

Materials
•    Five to 10 different colors of construction paper
•    Hole puncher
•    Bowl
•    Colored fabric or different color surface (optional)
•    Timer (optional)

Preparation
•    Using the hole puncher, punch out about 10 paper dots from each piece of paper. Each dot represents a different colored animal within the "dot" species.
•    Mix all of the paper dots in a bowl.
•    Spread the dots evenly over a surface in front of you. This surface represents the dots' environment, the habitat in which they live.

Procedure
•     You are a predator that uses vision to find your prey: paper dots.
•    Close your eyes.
•    Open your eyes and pick up the first dot that gets your attention.
•    Close your eyes again.
•    Open them again and pick up the first paper dot that gets your attention. Keep the dots that you pick in a pile off to the side.
•    Pick dots until you have "preyed upon" (picked up) about three quarters of the paper dots.

•    What dots are left? These dots have escaped the predator. Because they have survived, they can reproduce. For each dot remaining on the surface, punch out three more dots of the same color. The three new dots represent their offspring, which have the same traits and the same color. There should again be as many dots on the surface (or "habitat") as when you started.
•    Place the new "offspring" and "parent" dots in the bowl. Mix them up.
•    Again, spread the dots evenly over the surface and repeat the activity.
•    By the time you have done this three to four times, you have preyed upon several generations of paper dots and allowed only some of the population to survive and reproduce. Does the population of dots look different now than when you first started the activity?
•    Alternative: For a quicker version of this activity, you can spread out all of the dots on the tabletop or floor. Start the timer and have the "predator" pick up as many dots as he or she can in fifteen seconds. The dots that remain should be those that blend in to the environment the best. You can repeat as above, allowing these dots to reproduce offspring for the next generation.
•    Extra: For an even greater understanding of evolution by natural selection, repeat this experiment on a different colored surface (try using fabric or paper) and see if the population changes in a different way. How does the environment affect the traits that are common in a population?

Read on for observations, results and more resources.

1 Comments

1. 1. blindboy 08:30 PM 5/11/11

   This is a variation on a high school experiment that I have been doing for about thirty years. I was working with a teacher who was writing a biology text book when I first developed it and she included it in her book. In the original version I used plastic pieces or coloured toothpicks on grass. Other than that it is the same activity. I am happy to acknowledge that it could have occurred to others independently.

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