Natural Selection and Evolution: Using Multimedia Slide Shows to Emphasize the Role of Genetic Variation
Malone, Molly, Science Scope
Looking over my collection of natural-selection activities recently, I reflected on the understanding students end up taking away from them. Most middle school students comprehend that organisms have adaptations that enable their survival and that successful adaptations prevail in a population over time. Yet they often miss that those bird beaks, moth-wing colors, or whatever traits we track in our mock populations are the result of random, normal genetic variations that just happen to confer a negative, neutral, or positive survival advantage. Instead, many students hold on to the belief that adaptations arise in response to an environmental challenge and that this environmental pressure is what drives evolution.
Fortunately, a set of multimedia slide shows developed by the Genetic Science Learning Center at the University of Utah is taking aim at these commonly held misconceptions. By examining natural selection and evolution at the DNA level, they shift the focus from "adaptations" and place it on genetic variation instead. In this context, an organism's traits are the result of normal genetic processes and not a reaction to an environmental challenge. A genetic variation becomes "successful" in a population over time not because it is superior, but simply because individuals who possess it are alive to reproduce. Adding the slide shows as supplements to the activities you already use in your middle school classroom can help reinforce the concept that evolution is a natural process and not a response to a changing world.
I have selected the slide shows listed below from a larger collection of activities for their emphasis on genetic variation and appropriateness for the middle school level. They are all available for free at http://learn.genetics.utah.edu from the Variation, Selection, and Time module. A number of features support flexible use of the slide shows so they can be plugged in to what you already teach with minimal effort. They can be viewed in a computer lab with internet access (headphones are recommended) or projected for whole-group instruction. Toggle switches allow you to turn voice-overs and captions on and off. The "clickthrough" feature allows you to pace or supplement the slide shows, or you can jump to or revisit desired portions as you wish. To help you see where these slide shows might fortify your tried-and-true activities and jump-start your thinking, I have highlighted the key concepts for each one and provided ideas about how it could be used.
Recipe for evolution: Variation, selection, and time
Using animated graphics and minimal vocabulary, this introductory slide show (http://learn.genetics.utah.edu/content/variation/recipe) explains the three ingredients driving evolution: variation, selection, and time (Figure 1). Projected to the whole class, it makes a great introduction to a unit on evolution or natural selection. It also can help students distinguish between natural selection and evolution, which is sometimes hard to do.
Consider showing this slide show as a kickoff to your unit and using these three key ingredients as a theme throughout. As you complete simulation activities or present other examples of evolution, help students identify the variation, selective pressure, and an idea of elapsed time (in generations, years, or other relative quantity as appropriate). You can revisit all or portions of this slide show as needed.
Key concepts from this slide show are the following: Normal genetic processes (mutation and recombination) generate random variations. Natural selection affects which variations are kept and eliminated. Gradual changes over millions of years generate diversity among populations.
Sources of variation
Using photos of real-world traits such as eye color, this slide show (http://learn.genetics.utah.edu/content/variation/sources) explains in a simple manner how differences in DNA translate to diversity among individuals. …