The Roles of Chance and Natural Selection in Evolution

Class Time: 30-45 minutes

Materials:  Change by Chance Powerpoint  pen/pencil, transparencies (cut into 4” x 4” sheets), overhead projector  Alternative – 2’ x 2’ white boards and dry erase markers.

Summary This is an activity in which students see the role that chance, and natural selection play in evolution. This activity can be done to introduce evolution and natural selection, or can be done as a follow-up activity that challenges students to really begin to think about the intricacies of evolution. Students start off with a drawing of a lizard-like animal. The students (in mating pairs) attempt to reproduce (draw) the animal. The students then take on the role of the environment and choose which of the drawings in the class population would best be suited to the environment they are in.

Teacher Instructions:

 Start the activity by showing the students a picture of an environment in which the animal you are going to “evolve” lives in (see Change by Chance PowerPoint). Describe the characteristics of the environment to the students.  Pair up students (mating pairs) and provide each pair with several blank 4” x 4” transparencies and a Sharpie marker. Alternatively each pair can be provided a white board and a dry erase marker.  Show the drawing of the reptilian-like animal for the class. Each mating pair is to attempt to draw (reproduce) the animal on the overhead in 1 minute. The first student draws for the first 30 seconds, and the second student completes the animal in the last 30 seconds. Tell the mating pairs to try their best to copy the lizard picture. At the end of the time, tell the students to make sure that their animal at least has a head and four legs.  Once this is completed have several 5-8 mating pairs get together and decide which ONE of the “offspring” would be best suited to survive in the environment you described. Once they have decided, they should be prepared to describe what it is about the animal that suits it best to the environment. At the end of this selection process you should have several offspring that were selected by the groups of mating pairs. Show these to the class, and then have them vote on which of these remaining offspring would be best suited to the environment. Again, take some time to discuss why students voted for the most selected animal. Once the class has “selected” the best adapted animal, this becomes the animal that they will reproduce (draw in mating pairs) to again to produce the next generation offspring.  Repeat the above mating and selection process for 2-3 generations. Make sure you keep the drawing that was selected by the class for each generation, as you will display these to the class at the end of the activity so that they can see the changes that occurred in the lizards.  After several rounds of reproduction and selection, tell the students that your lizard population has now migrated to a new environment (i.e. “your animals have migrated to upland Longleaf pine forest..see picture in Change By Chance PowerPoint). Other options might be to a higher altitude on a mountain” or to a desert area, or to a subterranean cave etc…). Have the mating pairs (these can be the same as before or different pairs (i.e. a polygamous population)) and then attempt to draw the animal they selected as the most fit according to the same instructions as before. Again…have several mating pairs group up and select which of the newly drawn animals would be best suited to the environment, and then have the class select one of these to reproduce for the next generation of lizards. Have the students continue to do this for several generations.  At the end of the activity display all of the lizards that were selected for each generation on an overhead (or display the white boards across the front of the room) and discuss the changes in the population that occurred over time.

Homework or Class Discussion:

Have students write an essay or discuss some of the questions below.

 How were the changes observed similar to those that occur in populations according to Darwin’s theory? How were they different?  What biological processes did we simulate that resulted in the origin of new characteristics in each animal in the simulation? How similar was what occurred in the simulation to that which results in diversity within species in natural populations?  What were the sources of variation in our animal population from one generation to the next? How was this different and/or similar to generational variation observed in natural populations? If you had drawn the animal all by yourself (rather than in mating pairs) do you think your offspring would be more or less similar to the original? Why? What role do you think mating plays in the variation observed in natural populations? Why is variation important to the long-term success of populations?  Were there any instances during the simulation when someone purposely drew a characteristic on the animal that made it better suited to its environment? Do traits “purposefully” arise in nature? If so, explain how. If not, how do new traits arise?  Was sexual selection considered in our simulation? Explain.  If a paleontologist were to be studying your population of animals hundreds of thousands of years later, what problems might she encounter when trying to work out the evolutionary history of these organisms from fossil remains?

Standards:

Area I – Living Things Strand 3 – Change B. Explain how organisms adapt to environmental changes within communities and ecosystems. Strand 2 – Interactions A. Investigate the relationship between major biotic and abiotic components in ecosystems and communities. Strand 3 – Change D. Investigate and explain how the heredity of individuals and the genetics of a population are related to the process of natural selection. 2. The student will investigate and understand how population change through time. b. investigation how variation of traits, reproductive strategies, and environmental pressures impact the survival of populations. c. Recognizing how adaptations, heredity of individuals, and the genetics of populations lead to natural selection. d. Exploring how new species emerge by describing and explaining the role of genes, reproduction, and geographical barriers in the process of speciation.

Process Skills

A. Observe 1. Observe patterns of objects and events. D. Infer 1. The students will state generalizations G. Communicate 1. The students will communicate findings 3. The student will use scientific models to communicate information.